[RFC PATCH v4 00/28] Cache aware load-balancing

[RFC PATCH v4 00/28] Cache aware load-balancing

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

This is the forth revision of the cache aware scheduling
patches, based on the original patch proposed by Peter[1].

The main change in v4 is to address the performance regressions
reported in v3, which are caused by over-aggregation of tasks in
a single LLC, but they don't actually share data. Such aggregation
could cause regression on platforms with smaller LLC size. It can
also occur when running workloads with a large memory footprint
(e.g., stream) or when workloads involve too many threads
(e.g., hackbench).

Patches 1 to 20 are almost identical to those in v3; the key fixes
are included in patches 21 to 28. The approach involves tracking a
process's resident pages and comparing this to the LLC cache size.

To that effect, /sys/kernel/debug/sched/sched_cache_ignore_rss
is added where
0 turns off cache aware scheduling entirely
1 turns off cache aware scheduling when resident memory of process
  exceed LLC size (default)
100 RSS will not be taken into account during cache aware scheduling
N translates to turn off cache aware scheduling when RSS is
greater than (N-1) * 256 * LLC size

So for folks who want to make cache aware scheduling to
be aggressive and they know their process threads share lots of
data, they could set it to 100.

Similarly, the number of active threads within each process is
monitored and compared to the number of cores (excluding SMT) in
each LLC.

The second update is to limit the scan of a process's occupancy
for new preferred LLC candidate to preferred NUMA node from NUMA
balancing, node of current preferred LLC and node of current CPU.
It is very likely that these nodes overlap and reduces the scanning
cost. We also check to see if there are no NUMA node with more than
one LLC, cache aware scheduling is turned off and we will strictly
let NUMA balancing consolidate the tasks of a process.

v4 of cache aware scheduling relies only on load balancing to do
task aggregation as doing that during wake up is expensive. By
default, LLC task aggregation during wake-up is disabled.
Conversely, cache-aware load balancing is enabled by default.
For easier comparison, two scheduler features are introduced:
SCHED_CACHE_WAKE and SCHED_CACHE_LB,
which control cache-aware wake up and cache-aware load
balancing, respectively. We plan to obsolete SCHED_CACHE_WAKE
in future.

The load balancing and migration policy are now implemented in
a single location within the function _get_migrate_hint().
Debugfs knobs are also introduced to fine-tune the cache aware
load balancing. Please refer to patch 7 for detail.

Test results:
Tested on a 2 socket Intel Sapphire Rapids with 30 cores per
socket. The DRAM interleaving is enabled in the BIOS so it
essential has one NUMA node with two last level caches.
AMD Milan is also tested. There are 4 Nodes and 32 CPUs per node.
Each node has 4 CCX(shared LLC) and each CCX has 8 CPUs.

[TL;DR]
Sappire Rapids:
hackbench shows significant improvement when there is 1 group
with different number of fd pairs(threads) within this process.
schbench shows overall wakeup latency improvement.
Other micro-workloads did not show much difference.

Milan:
Regression in v3 has been mitigated a lot. For hackbench
and schbench, we still saw some regressions, and it can
be further tuned via debugfs to inhibit the cache aware
scheduling when it is overloaded.

[Sapphire Rapids details]
[hackbench]
Hackbench show overall improvement when there is only 1
group, with different number of fd(pairs). This is the
expected behavior because this test scenario would benefit
from cache aware load balance most. Other number of groups
shows not much difference(using default fd = 20).
                           baseline            sched_cache
         groups            hackbench              hackbench
Min       1      35.2340 (   0.00%)     27.2560 (  22.64%)
Min       3      36.0700 (   0.00%)     38.1750 (  -5.84%)
Min       5      36.4790 (   0.00%)     39.6540 (  -8.70%)
Min       7      51.2000 (   0.00%)     52.9050 (  -3.33%)
Min       12     63.1010 (   0.00%)     64.2940 (  -1.89%)
Min       16     75.0700 (   0.00%)     77.1050 (  -2.71%)
Amean     1      37.3802 (   0.00%)     28.0908 *  24.85%*
Amean     3      40.3703 (   0.00%)     40.1250 (   0.61%)
Amean     5      42.1782 (   0.00%)     41.4368 (   1.76%)
Amean     7      51.4848 (   0.00%)     53.3075 *  -3.54%*
Amean     12     63.6612 (   0.00%)     65.4685 (  -2.84%)
Amean     16     75.3333 (   0.00%)     78.5802 *  -4.31%*

[stream]
No much difference is observed.
512MB:
                         baseline_512        sched_cache_512
                        baseline_512M       sched_cache_512M
GB/sec copy-2        34.34 (   0.00%)       35.14 (   2.32%)
GB/sec scale-2       23.80 (   0.00%)       23.91 (   0.44%)
GB/sec add-2         28.89 (   0.00%)       28.92 (   0.12%)
GB/sec triad-2       28.62 (   0.00%)       28.67 (   0.17%)

2GB: 
                           baseline_2          sched_cache_2
                          baseline_2G         sched_cache_2G
GB/sec copy-2        35.68 (   0.00%)       36.03 (   0.97%)
GB/sec scale-2       23.85 (   0.00%)       23.83 (  -0.07%)
GB/sec add-2         28.47 (   0.00%)       28.42 (  -0.18%)
GB/sec triad-2       28.38 (   0.00%)       28.34 (  -0.15%)

[netperf]
No much difference is observed.

                          baseline            sched_cache
         nr_pairs          netperf                netperf
Hmean     1     1343.86 (   0.00%)     1344.58 (   0.05%)
BHmean-99 1     1346.54 (   0.00%)     1345.66 (  -0.07%)
Hmean     2     1322.98 (   0.00%)     1324.21 (   0.09%)
BHmean-99 2     1324.14 (   0.00%)     1325.78 (   0.12%)
Hmean     4     1327.85 (   0.00%)     1330.82 (   0.22%)
BHmean-99 4     1328.92 (   0.00%)     1331.68 (   0.21%)
Hmean     8     1313.72 (   0.00%)     1314.35 (   0.05%)
BHmean-99 8     1316.47 (   0.00%)     1315.65 (  -0.06%)
Hmean     16     1288.49 (   0.00%)     1294.18 (   0.44%)
BHmean-99 16     1290.63 (   0.00%)     1295.03 (   0.34%)
Hmean     32     1254.83 (   0.00%)     1260.84 (   0.48%)
BHmean-99 32     1258.50 (   0.00%)     1264.73 (   0.49%)
Hmean     64     1128.96 (   0.00%)     1127.00 (  -0.17%)
BHmean-99 64     1131.06 (   0.00%)     1127.83 (  -0.29%)
Hmean     128      799.18 (   0.00%)      796.50 (  -0.33%)
BHmean-99 128      802.29 (   0.00%)      799.37 (  -0.36%)
Hmean     256      400.59 (   0.00%)      399.65 (  -0.24%)
BHmean-99 256      402.76 (   0.00%)      401.76 (  -0.25%)

[schbench]
Overall 99.0th wakeup latency improvement is observed.

Metric                         Base (mean std)      Compare (mean std)   Change    
-------------------------------------------------------------------------------------
schbench thread = 1
Wakeup Latencies 99.0th        15.80(2.39)          14.60(1.52)          +7.59%    
Request Latencies 99.0th       3924.00(24.66)       3935.20(23.73)       -0.29%    
RPS 50.0th                     267.40(1.34)         266.40(1.34)         -0.37%    
Average RPS                    268.53(1.68)         267.57(1.46)         -0.36%    

schbench thread = 2
Wakeup Latencies 99.0th        17.20(0.45)          15.80(0.45)          +8.14%    
Request Latencies 99.0th       3900.00(11.31)       3914.40(31.19)       -0.37%    
RPS 50.0th                     537.00(0.00)         536.20(1.10)         -0.15%    
Average RPS                    537.80(0.25)         535.08(1.93)         -0.51%    

schbench thread = 4
Wakeup Latencies 99.0th        12.80(0.84)          12.40(0.55)          +3.13%    
Request Latencies 99.0th       3864.80(36.04)       3839.20(36.49)       +0.66%    
RPS 50.0th                     1076.40(2.19)        1077.20(1.79)        +0.07%    
Average RPS                    1074.00(2.43)        1073.44(2.24)        -0.05%    

schbench thread = 8
Wakeup Latencies 99.0th        13.60(1.67)          9.80(0.84)           +27.94%   
Request Latencies 99.0th       3746.40(22.20)       3794.40(32.69)       -1.28%    
RPS 50.0th                     2159.20(4.38)        2159.20(4.38)        0.00%     
Average RPS                    2155.74(2.77)        2154.16(1.86)        -0.07%    

schbench thread = 16
Wakeup Latencies 99.0th        12.60(1.52)          9.00(0.71)           +28.57%   
Request Latencies 99.0th       3775.20(26.29)       3783.20(15.59)       -0.21%    
RPS 50.0th                     4318.40(8.76)        4312.00(0.00)        -0.15%    
Average RPS                    4311.62(5.94)        4308.49(3.69)        -0.07%    

schbench thread = 32
Wakeup Latencies 99.0th        12.20(0.45)          8.80(0.84)           +27.87%   
Request Latencies 99.0th       3781.60(27.36)       3812.00(23.32)       -0.80%    
RPS 50.0th                     8630.40(14.31)       8630.40(14.31)       0.00%     
Average RPS                    8621.32(3.34)        8614.98(8.24)        -0.07%    

schbench thread = 64
Wakeup Latencies 99.0th        12.60(0.55)          10.20(1.10)          +19.05%   
Request Latencies 99.0th       3778.40(19.10)       5498.40(2130.50)     -45.52%   
RPS 50.0th                     17248.00(0.00)       16774.40(560.98)     -2.75%    
Average RPS                    17249.44(6.83)       16727.70(544.81)     -3.02%    

schbench thread = 128
Wakeup Latencies 99.0th        14.00(0.00)          14.40(0.55)          -2.86%    
Request Latencies 99.0th       7860.80(7.16)        8123.20(20.86)       -3.34%    
RPS 50.0th                     32147.20(145.94)     29587.20(2081.43)    -7.96%    
Average RPS                    31546.92(444.17)     28827.07(1842.18)    -8.62%    

schbench thread = 239
Wakeup Latencies 99.0th        41.60(2.07)          39.20(2.05)          +5.77%    
Request Latencies 99.0th       8056.00(0.00)        8361.60(26.77)       -3.79%    
RPS 50.0th                     31020.80(28.62)      30137.60(57.24)      -2.85%    
Average RPS                    31052.18(32.53)      30158.53(47.73)      -2.88%    


[Milan details]
[hackbench]
Regressions are observed when many hackbench instances are
running simultaneously. Considering that the per-process
nr_running statistic is tracked in v4, reintroducing the
per-LLC nr_running statistic (as in v1/v2) might mitigate
the regression (and could be implemented in v5).

                           baseline            sched_cache
                          hackbench              hackbench
Min       1      50.8910 (   0.00%)     51.3470 (  -0.90%)
Min       3      51.1380 (   0.00%)     52.1710 (  -2.02%)
Min       5      75.5740 (   0.00%)     79.9060 (  -5.73%)
Min       7     106.0020 (   0.00%)    111.6930 (  -5.37%)
Min       12    177.3530 (   0.00%)    195.9230 ( -10.47%)
Min       16    238.8580 (   0.00%)    268.5540 ( -12.43%)
Amean     1      52.0164 (   0.00%)     52.0198 (  -0.01%)
Amean     3      51.6346 (   0.00%)     52.9120 (  -2.47%)
Amean     5      76.9840 (   0.00%)     81.1256 (  -5.38%)
Amean     7     107.1258 (   0.00%)    112.5528 *  -5.07%*
Amean     12    178.5502 (   0.00%)    197.8780 * -10.82%*
Amean     16    240.5200 (   0.00%)    270.3840 * -12.42%*

[stream]
No huge regression is observed, which was seen in v3.

512MB:
                         baseline_512        sched_cache_512
                        baseline_512M       sched_cache_512M
GB/sec copy-16       442.53 (   0.00%)      421.83 (  -4.68%)
GB/sec scale-16      387.74 (   0.00%)      377.00 (  -2.77%)
GB/sec add-16        413.29 (   0.00%)      410.84 (  -0.59%)
GB/sec triad-16      411.34 (   0.00%)      407.73 (  -0.88%)

2GB: 
                           baseline_2          sched_cache_2
                          baseline_2G         sched_cache_2G
GB/sec copy-16       309.30 (   0.00%)      315.93 (   2.15%)
GB/sec scale-16      208.16 (   0.00%)      209.99 (   0.88%)
GB/sec add-16        229.94 (   0.00%)      231.51 (   0.68%)
GB/sec triad-16      240.40 (   0.00%)      242.02 (   0.67%)


[netperf]
No much difference is observed.

                          baseline            sched_cache
         nr_pairs          netperf                netperf
Hmean     1      919.00 (   0.00%)      923.82 (   0.52%)
BHmean-99 1      920.38 (   0.00%)      925.34 (   0.54%)
Hmean     2      917.23 (   0.00%)      916.01 (  -0.13%)
BHmean-99 2      918.99 (   0.00%)      918.08 (  -0.10%)
Hmean     4      908.65 (   0.00%)      908.47 (  -0.02%)
BHmean-99 4      910.04 (   0.00%)      909.56 (  -0.05%)
Hmean     8      911.31 (   0.00%)      909.19 (  -0.23%)
BHmean-99 8      911.97 (   0.00%)      910.23 (  -0.19%)
Hmean     16      905.37 (   0.00%)      901.83 (  -0.39%)
BHmean-99 16      905.92 (   0.00%)      902.43 (  -0.39%)
Hmean     32      865.56 (   0.00%)      860.52 (  -0.58%)
BHmean-99 32      866.40 (   0.00%)      863.23 (  -0.37%)
Hmean     64      734.50 (   0.00%)      729.11 (  -0.73%)
BHmean-99 64      737.50 (   0.00%)      732.97 (  -0.61%)
Hmean     128      735.01 (   0.00%)      728.00 (  -0.95%)
BHmean-99 128      738.62 (   0.00%)      731.48 (  -0.97%)
Hmean     256      335.52 (   0.00%)      335.57 (   0.01%)
BHmean-99 256      338.19 (   0.00%)      337.99 (  -0.06%)

[schbench]

No huge regression is observed(consider the std), which
was seen in v3.

Metric                         Base (mean std)      Compare (mean std)   Change    
-------------------------------------------------------------------------------------
schbench thread = 1
Wakeup Latencies 99.0th        14.80(1.10)          15.00(2.74)          -1.35%    
Request Latencies 99.0th       5310.40(18.24)       5342.40(56.11)       -0.60%    
RPS 50.0th                     384.20(3.27)         386.00(5.43)         +0.47%    
Average RPS                    385.94(1.98)         387.37(4.74)         +0.37%    

schbench thread = 2
Wakeup Latencies 99.0th        15.20(0.45)          16.80(1.30)          -10.53%   
Request Latencies 99.0th       5291.20(7.16)        5336.00(27.71)       -0.85%    
RPS 50.0th                     778.60(2.61)         772.20(7.01)         -0.82%    
Average RPS                    778.54(2.42)         773.14(6.19)         -0.69%    

schbench thread = 4
Wakeup Latencies 99.0th        16.60(1.52)          17.60(0.55)          -6.02%    
Request Latencies 99.0th       5233.60(8.76)        7432.00(2946.91)     -42.01%   
RPS 50.0th                     1578.80(1.79)        1570.00(9.38)        -0.56%    
Average RPS                    1576.94(1.88)        1544.12(44.90)       -2.08%    

schbench thread = 8
Wakeup Latencies 99.0th        18.40(0.89)          19.40(0.55)          -5.43%    
Request Latencies 99.0th       5236.80(7.16)        5236.80(7.16)        0.00%     
RPS 50.0th                     3152.80(4.38)        3148.00(0.00)        -0.15%    
Average RPS                    3150.89(2.71)        3145.30(1.21)        -0.18%    

schbench thread = 16
Wakeup Latencies 99.0th        16.80(1.64)          18.40(0.55)          -9.52%    
Request Latencies 99.0th       5224.00(0.00)        5195.20(47.19)       +0.55%    
RPS 50.0th                     6312.00(0.00)        6296.00(0.00)        -0.25%    
Average RPS                    6308.84(3.79)        6293.32(2.61)        -0.25%    

schbench thread = 32
Wakeup Latencies 99.0th        18.80(2.17)          21.00(0.71)          -11.70%   
Request Latencies 99.0th       9716.80(2458.04)     10806.40(35.05)      -11.21%   
RPS 50.0th                     12457.60(79.68)      12483.20(62.38)      +0.21%    
Average RPS                    12300.14(125.37)     12269.54(66.16)      -0.25%    

schbench thread = 63
Wakeup Latencies 99.0th        27.20(0.45)          29.00(0.71)          -6.62%    
Request Latencies 99.0th       11337.60(14.31)      11401.60(14.31)      -0.56%    
RPS 50.0th                     11632.00(0.00)       11600.00(0.00)       -0.28%    
Average RPS                    11628.59(1.85)       11597.09(2.17)       -0.27%    
-------------------------------------------------------------------------------------

This patch set is applied on vanilla v6.16 kernel.
Thanks to Yangyu Chen, K Prateek Nayak, Shrikanth Hegde, Libo Chen,
Jianyong Wu, and Madadi Vineeth Reddy for their testing and valuable
suggestions on v3. Since the code has been modified, Yangyu's Tested-by tag
has not been included in v4.

Comments and tests are much appreciated.

Patch 1:     Peter's original patch.
Patch 2-5:   Various fixes and tuning of the original v1 patch.
Patch 6-12:  Infrastructure and helper functions for load balancing to be cache aware.
Patch 13-18: Add logic to load balancing for preferred LLC aggregation.
Patch 19:    Add process LLC aggregation in load balancing sched feature.
Patch 20:    Add Process LLC aggregation in wake up sched feature (turn off by default).
Patch 21-28: Fix the performance regressions reported in v3, by checking
             the process's working set and number of active threads, finding
             the busiest CPU in the preferred NUMA node.

v1:
https://lore.kernel.org/lkml/20250325120952.GJ36322@noisy.programming.kicks-ass.net/
v2:
https://lore.kernel.org/lkml/cover.1745199017.git.yu.c.chen@intel.com/
v3:
https://lore.kernel.org/all/cover.1750268218.git.tim.c.chen@linux.intel.com/

Chen Yu (11):
  sched: Several fixes for cache aware scheduling
  sched: Avoid task migration within its preferred LLC
  sched: Save the per LLC utilization for better cache aware scheduling
  sched: Introduce a static key to enable cache aware only for multi
    LLCs
  sched: Turn EPOCH_PERIOD and EPOCH_OLD into tunnable debugfs
  sched: Scan a task's preferred node for preferred LLC
  sched: Record average number of runninhg tasks per process
  sched: Skip cache aware scheduling if the process has many active
    threads
  sched: Do not enable cache aware scheduling for process with large RSS
  sched: Allow the user space to tune the scale factor for RSS
    comparison
  sched: Add ftrace to track cache aware load balance and hottest CPU
    changes

K Prateek Nayak (1):
  sched: Avoid calculating the cpumask if the system is overloaded

Peter Zijlstra (1):
  sched: Cache aware load-balancing

Tim Chen (15):
  sched: Add hysteresis to switch a task's preferred LLC
  sched: Add helper function to decide whether to allow cache aware
    scheduling
  sched: Set up LLC indexing
  sched: Introduce task preferred LLC field
  sched: Calculate the number of tasks that have LLC preference on a
    runqueue
  sched: Introduce per runqueue task LLC preference counter
  sched: Calculate the total number of preferred LLC tasks during load
    balance
  sched: Tag the sched group as llc_balance if it has tasks prefer other
    LLC
  sched: Introduce update_llc_busiest() to deal with groups having
    preferred LLC tasks
  sched: Introduce a new migration_type to track the preferred LLC load
    balance
  sched: Consider LLC locality for active balance
  sched: Consider LLC preference when picking tasks from busiest queue
  sched: Do not migrate task if it is moving out of its preferred LLC
  sched: Introduce SCHED_CACHE_LB to control cache aware load balance
  sched: Introduce SCHED_CACHE_WAKE to control LLC aggregation on wake
    up

 include/linux/mm_types.h       |   45 ++
 include/linux/sched.h          |    8 +
 include/linux/sched/topology.h |    3 +
 include/trace/events/sched.h   |   93 +++
 init/Kconfig                   |    8 +
 init/init_task.c               |    3 +
 kernel/fork.c                  |    5 +
 kernel/sched/core.c            |   25 +-
 kernel/sched/debug.c           |   86 +++
 kernel/sched/fair.c            | 1022 +++++++++++++++++++++++++++++++-
 kernel/sched/features.h        |    3 +
 kernel/sched/sched.h           |   27 +
 kernel/sched/topology.c        |   51 +-
 13 files changed, 1348 insertions(+), 31 deletions(-)

-- 
2.25.1

[RFC PATCH v4 01/28] sched: Cache aware load-balancing

[Chen Yu]

From: Peter Zijlstra <peterz@infradead.org>

Hi all,

One of the many things on the eternal todo list has been finishing the
below hackery.

It is an attempt at modelling cache affinity -- and while the patch
really only targets LLC, it could very well be extended to also apply to
clusters (L2). Specifically any case of multiple cache domains inside a
node.

Anyway, I wrote this about a year ago, and I mentioned this at the
recent OSPM conf where Gautham and Prateek expressed interest in playing
with this code.

So here goes, very rough and largely unproven code ahead :-)

It applies to current tip/master, but I know it will fail the __percpu
validation that sits in -next, although that shouldn't be terribly hard
to fix up.

As is, it only computes a CPU inside the LLC that has the highest recent
runtime, this CPU is then used in the wake-up path to steer towards this
LLC and in task_hot() to limit migrations away from it.

More elaborate things could be done, notably there is an XXX in there
somewhere about finding the best LLC inside a NODE (interaction with
NUMA_BALANCING).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/mm_types.h |  44 ++++++
 include/linux/sched.h    |   4 +
 init/Kconfig             |   4 +
 kernel/fork.c            |   5 +
 kernel/sched/core.c      |  13 +-
 kernel/sched/fair.c      | 330 +++++++++++++++++++++++++++++++++++++--
 kernel/sched/sched.h     |   8 +
 7 files changed, 388 insertions(+), 20 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index d6b91e8a66d6..cf26ad8b41ab 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -928,6 +928,12 @@ struct mm_cid {
 };
 #endif
 
+struct mm_sched {
+	u64 runtime;
+	unsigned long epoch;
+	unsigned long occ;
+};
+
 struct kioctx_table;
 struct iommu_mm_data;
 struct mm_struct {
@@ -1018,6 +1024,17 @@ struct mm_struct {
 		 */
 		raw_spinlock_t cpus_allowed_lock;
 #endif
+#ifdef CONFIG_SCHED_CACHE
+		/*
+		 * Track per-cpu-per-process occupancy as a proxy for cache residency.
+		 * See account_mm_sched() and ...
+		 */
+		struct mm_sched __percpu *pcpu_sched;
+		raw_spinlock_t mm_sched_lock;
+		unsigned long mm_sched_epoch;
+		int mm_sched_cpu;
+#endif
+
 #ifdef CONFIG_MMU
 		atomic_long_t pgtables_bytes;	/* size of all page tables */
 #endif
@@ -1432,6 +1449,33 @@ static inline unsigned int mm_cid_size(void)
 static inline void mm_set_cpus_allowed(struct mm_struct *mm, const struct cpumask *cpumask) { }
 #endif /* CONFIG_SCHED_MM_CID */
 
+#ifdef CONFIG_SCHED_CACHE
+extern void mm_init_sched(struct mm_struct *mm, struct mm_sched *pcpu_sched);
+
+static inline int mm_alloc_sched_noprof(struct mm_struct *mm)
+{
+	struct mm_sched *pcpu_sched = alloc_percpu_noprof(struct mm_sched);
+	if (!pcpu_sched)
+		return -ENOMEM;
+
+	mm_init_sched(mm, pcpu_sched);
+	return 0;
+}
+
+#define mm_alloc_sched(...)	alloc_hooks(mm_alloc_sched_noprof(__VA_ARGS__))
+
+static inline void mm_destroy_sched(struct mm_struct *mm)
+{
+	free_percpu(mm->pcpu_sched);
+	mm->pcpu_sched = NULL;
+}
+#else /* !CONFIG_SCHED_CACHE */
+
+static inline int mm_alloc_sched(struct mm_struct *mm) { return 0; }
+static inline void mm_destroy_sched(struct mm_struct *mm) { }
+
+#endif /* CONFIG_SCHED_CACHE */
+
 struct mmu_gather;
 extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm);
 extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index aa9c5be7a632..02ff8b8be25b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1403,6 +1403,10 @@ struct task_struct {
 	unsigned long			numa_pages_migrated;
 #endif /* CONFIG_NUMA_BALANCING */
 
+#ifdef CONFIG_SCHED_CACHE
+	struct callback_head		cache_work;
+#endif
+
 #ifdef CONFIG_RSEQ
 	struct rseq __user *rseq;
 	u32 rseq_len;
diff --git a/init/Kconfig b/init/Kconfig
index 666783eb50ab..27f4012347f9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -947,6 +947,10 @@ config NUMA_BALANCING
 
 	  This system will be inactive on UMA systems.
 
+config SCHED_CACHE
+	bool "Cache aware scheduler"
+	default y
+
 config NUMA_BALANCING_DEFAULT_ENABLED
 	bool "Automatically enable NUMA aware memory/task placement"
 	default y
diff --git a/kernel/fork.c b/kernel/fork.c
index 1ee8eb11f38b..546c49e46d48 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1073,6 +1073,9 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	if (mm_alloc_cid(mm, p))
 		goto fail_cid;
 
+	if (mm_alloc_sched(mm))
+		goto fail_sched;
+
 	if (percpu_counter_init_many(mm->rss_stat, 0, GFP_KERNEL_ACCOUNT,
 				     NR_MM_COUNTERS))
 		goto fail_pcpu;
@@ -1082,6 +1085,8 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	return mm;
 
 fail_pcpu:
+	mm_destroy_sched(mm);
+fail_sched:
 	mm_destroy_cid(mm);
 fail_cid:
 	destroy_context(mm);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 81c6df746df1..a5fb3057b1c4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4539,6 +4539,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 	p->migration_pending = NULL;
 #endif
 	init_sched_mm_cid(p);
+	init_sched_mm(p);
 }
 
 DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);
@@ -8508,6 +8509,7 @@ static struct kmem_cache *task_group_cache __ro_after_init;
 
 void __init sched_init(void)
 {
+	unsigned long now = jiffies;
 	unsigned long ptr = 0;
 	int i;
 
@@ -8582,7 +8584,7 @@ void __init sched_init(void)
 		raw_spin_lock_init(&rq->__lock);
 		rq->nr_running = 0;
 		rq->calc_load_active = 0;
-		rq->calc_load_update = jiffies + LOAD_FREQ;
+		rq->calc_load_update = now + LOAD_FREQ;
 		init_cfs_rq(&rq->cfs);
 		init_rt_rq(&rq->rt);
 		init_dl_rq(&rq->dl);
@@ -8626,7 +8628,7 @@ void __init sched_init(void)
 		rq->cpu_capacity = SCHED_CAPACITY_SCALE;
 		rq->balance_callback = &balance_push_callback;
 		rq->active_balance = 0;
-		rq->next_balance = jiffies;
+		rq->next_balance = now;
 		rq->push_cpu = 0;
 		rq->cpu = i;
 		rq->online = 0;
@@ -8638,7 +8640,7 @@ void __init sched_init(void)
 
 		rq_attach_root(rq, &def_root_domain);
 #ifdef CONFIG_NO_HZ_COMMON
-		rq->last_blocked_load_update_tick = jiffies;
+		rq->last_blocked_load_update_tick = now;
 		atomic_set(&rq->nohz_flags, 0);
 
 		INIT_CSD(&rq->nohz_csd, nohz_csd_func, rq);
@@ -8663,6 +8665,11 @@ void __init sched_init(void)
 
 		rq->core_cookie = 0UL;
 #endif
+#ifdef CONFIG_SCHED_CACHE
+		raw_spin_lock_init(&rq->cpu_epoch_lock);
+		rq->cpu_epoch_next = now;
+#endif
+
 		zalloc_cpumask_var_node(&rq->scratch_mask, GFP_KERNEL, cpu_to_node(i));
 	}
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7a14da5396fb..e3897cd7696d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1166,10 +1166,229 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 	return delta_exec;
 }
 
-static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
+#ifdef CONFIG_SCHED_CACHE
+
+/*
+ * XXX numbers come from a place the sun don't shine -- probably wants to be SD
+ * tunable or so.
+ */
+#define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
+#define EPOCH_OLD	5		/* 50 ms */
+
+void mm_init_sched(struct mm_struct *mm, struct mm_sched *_pcpu_sched)
+{
+	unsigned long epoch;
+	int i;
+
+	for_each_possible_cpu(i) {
+		struct mm_sched *pcpu_sched = per_cpu_ptr(_pcpu_sched, i);
+		struct rq *rq = cpu_rq(i);
+
+		pcpu_sched->runtime = 0;
+		pcpu_sched->epoch = epoch = rq->cpu_epoch;
+		pcpu_sched->occ = -1;
+	}
+
+	raw_spin_lock_init(&mm->mm_sched_lock);
+	mm->mm_sched_epoch = epoch;
+	mm->mm_sched_cpu = -1;
+
+	smp_store_release(&mm->pcpu_sched, _pcpu_sched);
+}
+
+/* because why would C be fully specified */
+static __always_inline void __shr_u64(u64 *val, unsigned int n)
+{
+	if (n >= 64) {
+		*val = 0;
+		return;
+	}
+	*val >>= n;
+}
+
+static inline void __update_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
+{
+	lockdep_assert_held(&rq->cpu_epoch_lock);
+
+	unsigned long n, now = jiffies;
+	long delta = now - rq->cpu_epoch_next;
+
+	if (delta > 0) {
+		n = (delta + EPOCH_PERIOD - 1) / EPOCH_PERIOD;
+		rq->cpu_epoch += n;
+		rq->cpu_epoch_next += n * EPOCH_PERIOD;
+		__shr_u64(&rq->cpu_runtime, n);
+	}
+
+	n = rq->cpu_epoch - pcpu_sched->epoch;
+	if (n) {
+		pcpu_sched->epoch += n;
+		__shr_u64(&pcpu_sched->runtime, n);
+	}
+}
+
+static unsigned long fraction_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
+{
+	guard(raw_spinlock_irqsave)(&rq->cpu_epoch_lock);
+
+	__update_mm_sched(rq, pcpu_sched);
+
+	/*
+	 * Runtime is a geometric series (r=0.5) and as such will sum to twice
+	 * the accumulation period, this means the multiplcation here should
+	 * not overflow.
+	 */
+	return div64_u64(NICE_0_LOAD * pcpu_sched->runtime, rq->cpu_runtime + 1);
+}
+
+static inline
+void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
+{
+	struct mm_struct *mm = p->mm;
+	struct mm_sched *pcpu_sched;
+	unsigned long epoch;
+
+	/*
+	 * init_task and kthreads don't be having no mm
+	 */
+	if (!mm || !mm->pcpu_sched)
+		return;
+
+	pcpu_sched = this_cpu_ptr(p->mm->pcpu_sched);
+
+	scoped_guard (raw_spinlock, &rq->cpu_epoch_lock) {
+		__update_mm_sched(rq, pcpu_sched);
+		pcpu_sched->runtime += delta_exec;
+		rq->cpu_runtime += delta_exec;
+		epoch = rq->cpu_epoch;
+	}
+
+	/*
+	 * If this task hasn't hit task_cache_work() for a while, invalidate
+	 * it's preferred state.
+	 */
+	if (epoch - READ_ONCE(mm->mm_sched_epoch) > EPOCH_OLD) {
+		mm->mm_sched_cpu = -1;
+		pcpu_sched->occ = -1;
+	}
+}
+
+static void task_tick_cache(struct rq *rq, struct task_struct *p)
+{
+	struct callback_head *work = &p->cache_work;
+	struct mm_struct *mm = p->mm;
+
+	if (!mm || !mm->pcpu_sched)
+		return;
+
+	if (mm->mm_sched_epoch == rq->cpu_epoch)
+		return;
+
+	guard(raw_spinlock)(&mm->mm_sched_lock);
+
+	if (mm->mm_sched_epoch == rq->cpu_epoch)
+		return;
+
+	if (work->next == work) {
+		task_work_add(p, work, TWA_RESUME);
+		WRITE_ONCE(mm->mm_sched_epoch, rq->cpu_epoch);
+	}
+}
+
+static void task_cache_work(struct callback_head *work)
+{
+	struct task_struct *p = current;
+	struct mm_struct *mm = p->mm;
+	unsigned long m_a_occ = 0;
+	int cpu, m_a_cpu = -1;
+	cpumask_var_t cpus;
+
+	WARN_ON_ONCE(work != &p->cache_work);
+
+	work->next = work;
+
+	if (p->flags & PF_EXITING)
+		return;
+
+	if (!alloc_cpumask_var(&cpus, GFP_KERNEL))
+		return;
+
+	scoped_guard (cpus_read_lock) {
+		cpumask_copy(cpus, cpu_online_mask);
+
+		for_each_cpu(cpu, cpus) {
+			/* XXX sched_cluster_active */
+			struct sched_domain *sd = per_cpu(sd_llc, cpu);
+			unsigned long occ, m_occ = 0, a_occ = 0;
+			int m_cpu = -1, nr = 0, i;
+
+			for_each_cpu(i, sched_domain_span(sd)) {
+				occ = fraction_mm_sched(cpu_rq(i),
+							per_cpu_ptr(mm->pcpu_sched, i));
+				a_occ += occ;
+				if (occ > m_occ) {
+					m_occ = occ;
+					m_cpu = i;
+				}
+				nr++;
+				trace_printk("(%d) occ: %ld m_occ: %ld m_cpu: %d nr: %d\n",
+					     per_cpu(sd_llc_id, i), occ, m_occ, m_cpu, nr);
+			}
+
+			a_occ /= nr;
+			if (a_occ > m_a_occ) {
+				m_a_occ = a_occ;
+				m_a_cpu = m_cpu;
+			}
+
+			trace_printk("(%d) a_occ: %ld m_a_occ: %ld\n",
+				     per_cpu(sd_llc_id, cpu), a_occ, m_a_occ);
+
+			for_each_cpu(i, sched_domain_span(sd)) {
+				/* XXX threshold ? */
+				per_cpu_ptr(mm->pcpu_sched, i)->occ = a_occ;
+			}
+
+			cpumask_andnot(cpus, cpus, sched_domain_span(sd));
+		}
+	}
+
+	/*
+	 * If the max average cache occupancy is 'small' we don't care.
+	 */
+	if (m_a_occ < (NICE_0_LOAD >> EPOCH_OLD))
+		m_a_cpu = -1;
+
+	mm->mm_sched_cpu = m_a_cpu;
+
+	free_cpumask_var(cpus);
+}
+
+void init_sched_mm(struct task_struct *p)
+{
+	struct callback_head *work = &p->cache_work;
+	init_task_work(work, task_cache_work);
+	work->next = work;
+}
+
+#else
+
+static inline void account_mm_sched(struct rq *rq, struct task_struct *p,
+				    s64 delta_exec) { }
+
+
+void init_sched_mm(struct task_struct *p) { }
+
+static void task_tick_cache(struct rq *rq, struct task_struct *p) { }
+
+#endif
+
+static inline
+void update_curr_task(struct rq *rq, struct task_struct *p, s64 delta_exec)
 {
 	trace_sched_stat_runtime(p, delta_exec);
 	account_group_exec_runtime(p, delta_exec);
+	account_mm_sched(rq, p, delta_exec);
 	cgroup_account_cputime(p, delta_exec);
 }
 
@@ -1215,7 +1434,7 @@ s64 update_curr_common(struct rq *rq)
 
 	delta_exec = update_curr_se(rq, &donor->se);
 	if (likely(delta_exec > 0))
-		update_curr_task(donor, delta_exec);
+		update_curr_task(rq, donor, delta_exec);
 
 	return delta_exec;
 }
@@ -1244,7 +1463,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	if (entity_is_task(curr)) {
 		struct task_struct *p = task_of(curr);
 
-		update_curr_task(p, delta_exec);
+		update_curr_task(rq, p, delta_exec);
 
 		/*
 		 * If the fair_server is active, we need to account for the
@@ -7862,7 +8081,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	 * per-cpu select_rq_mask usage
 	 */
 	lockdep_assert_irqs_disabled();
-
+again:
 	if ((available_idle_cpu(target) || sched_idle_cpu(target)) &&
 	    asym_fits_cpu(task_util, util_min, util_max, target))
 		return target;
@@ -7900,7 +8119,8 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	/* Check a recently used CPU as a potential idle candidate: */
 	recent_used_cpu = p->recent_used_cpu;
 	p->recent_used_cpu = prev;
-	if (recent_used_cpu != prev &&
+	if (prev == p->wake_cpu &&
+	    recent_used_cpu != prev &&
 	    recent_used_cpu != target &&
 	    cpus_share_cache(recent_used_cpu, target) &&
 	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
@@ -7953,6 +8173,18 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	if ((unsigned)i < nr_cpumask_bits)
 		return i;
 
+	if (prev != p->wake_cpu && !cpus_share_cache(prev, p->wake_cpu)) {
+		/*
+		 * Most likely select_cache_cpu() will have re-directed
+		 * the wakeup, but getting here means the preferred cache is
+		 * too busy, so re-try with the actual previous.
+		 *
+		 * XXX wake_affine is lost for this pass.
+		 */
+		prev = target = p->wake_cpu;
+		goto again;
+	}
+
 	/*
 	 * For cluster machines which have lower sharing cache like L2 or
 	 * LLC Tag, we tend to find an idle CPU in the target's cluster
@@ -8575,6 +8807,40 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 	return target;
 }
 
+#ifdef CONFIG_SCHED_CACHE
+static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle);
+
+static int select_cache_cpu(struct task_struct *p, int prev_cpu)
+{
+	struct mm_struct *mm = p->mm;
+	int cpu;
+
+	if (!mm || p->nr_cpus_allowed == 1)
+		return prev_cpu;
+
+	cpu = mm->mm_sched_cpu;
+	if (cpu < 0)
+		return prev_cpu;
+
+
+	if (static_branch_likely(&sched_numa_balancing) &&
+	    __migrate_degrades_locality(p, prev_cpu, cpu, false) > 0) {
+		/*
+		 * XXX look for max occupancy inside prev_cpu's node
+		 */
+		return prev_cpu;
+	}
+
+	return cpu;
+}
+#else
+static int select_cache_cpu(struct task_struct *p, int prev_cpu)
+{
+	return prev_cpu;
+}
+#endif
+
+
 /*
  * select_task_rq_fair: Select target runqueue for the waking task in domains
  * that have the relevant SD flag set. In practice, this is SD_BALANCE_WAKE,
@@ -8600,6 +8866,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 	 * required for stable ->cpus_allowed
 	 */
 	lockdep_assert_held(&p->pi_lock);
+	guard(rcu)();
+
 	if (wake_flags & WF_TTWU) {
 		record_wakee(p);
 
@@ -8607,6 +8875,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 		    cpumask_test_cpu(cpu, p->cpus_ptr))
 			return cpu;
 
+		new_cpu = prev_cpu = select_cache_cpu(p, prev_cpu);
+
 		if (!is_rd_overutilized(this_rq()->rd)) {
 			new_cpu = find_energy_efficient_cpu(p, prev_cpu);
 			if (new_cpu >= 0)
@@ -8617,7 +8887,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 		want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, p->cpus_ptr);
 	}
 
-	rcu_read_lock();
 	for_each_domain(cpu, tmp) {
 		/*
 		 * If both 'cpu' and 'prev_cpu' are part of this domain,
@@ -8650,7 +8919,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 		/* Fast path */
 		new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
 	}
-	rcu_read_unlock();
 
 	return new_cpu;
 }
@@ -9300,6 +9568,17 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 	if (sysctl_sched_migration_cost == 0)
 		return 0;
 
+#ifdef CONFIG_SCHED_CACHE
+	if (p->mm && p->mm->pcpu_sched) {
+		/*
+		 * XXX things like Skylake have non-inclusive L3 and might not
+		 * like this L3 centric view. What to do about L2 stickyness ?
+		 */
+		return per_cpu_ptr(p->mm->pcpu_sched, env->src_cpu)->occ >
+		       per_cpu_ptr(p->mm->pcpu_sched, env->dst_cpu)->occ;
+	}
+#endif
+
 	delta = rq_clock_task(env->src_rq) - p->se.exec_start;
 
 	return delta < (s64)sysctl_sched_migration_cost;
@@ -9311,27 +9590,25 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
  * Returns 0, if task migration is not affected by locality.
  * Returns a negative value, if task migration improves locality i.e migration preferred.
  */
-static long migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
+static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle)
 {
 	struct numa_group *numa_group = rcu_dereference(p->numa_group);
 	unsigned long src_weight, dst_weight;
 	int src_nid, dst_nid, dist;
 
-	if (!static_branch_likely(&sched_numa_balancing))
-		return 0;
-
-	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
+	if (!p->numa_faults)
 		return 0;
 
-	src_nid = cpu_to_node(env->src_cpu);
-	dst_nid = cpu_to_node(env->dst_cpu);
+	src_nid = cpu_to_node(src_cpu);
+	dst_nid = cpu_to_node(dst_cpu);
 
 	if (src_nid == dst_nid)
 		return 0;
 
 	/* Migrating away from the preferred node is always bad. */
 	if (src_nid == p->numa_preferred_nid) {
-		if (env->src_rq->nr_running > env->src_rq->nr_preferred_running)
+		struct rq *src_rq = cpu_rq(src_cpu);
+		if (src_rq->nr_running > src_rq->nr_preferred_running)
 			return 1;
 		else
 			return 0;
@@ -9342,7 +9619,7 @@ static long migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 		return -1;
 
 	/* Leaving a core idle is often worse than degrading locality. */
-	if (env->idle == CPU_IDLE)
+	if (idle)
 		return 0;
 
 	dist = node_distance(src_nid, dst_nid);
@@ -9357,7 +9634,24 @@ static long migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 	return src_weight - dst_weight;
 }
 
+static long migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
+{
+	if (!static_branch_likely(&sched_numa_balancing))
+		return 0;
+
+	if (!(env->sd->flags & SD_NUMA))
+		return 0;
+
+	return __migrate_degrades_locality(p, env->src_cpu, env->dst_cpu,
+					   env->idle == CPU_IDLE);
+}
+
 #else
+static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle)
+{
+	return 0;
+}
+
 static inline long migrate_degrades_locality(struct task_struct *p,
 					     struct lb_env *env)
 {
@@ -13117,8 +13411,8 @@ static inline void task_tick_core(struct rq *rq, struct task_struct *curr) {}
  */
 static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 {
-	struct cfs_rq *cfs_rq;
 	struct sched_entity *se = &curr->se;
+	struct cfs_rq *cfs_rq;
 
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
@@ -13128,6 +13422,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 	if (static_branch_unlikely(&sched_numa_balancing))
 		task_tick_numa(rq, curr);
 
+	task_tick_cache(rq, curr);
+
 	update_misfit_status(curr, rq);
 	check_update_overutilized_status(task_rq(curr));
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 83e3aa917142..839463027ab0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1173,6 +1173,12 @@ struct rq {
 	u64			clock_pelt_idle_copy;
 	u64			clock_idle_copy;
 #endif
+#ifdef CONFIG_SCHED_CACHE
+	raw_spinlock_t		cpu_epoch_lock;
+	u64			cpu_runtime;
+	unsigned long		cpu_epoch;
+	unsigned long		cpu_epoch_next;
+#endif
 
 	atomic_t		nr_iowait;
 
@@ -3885,6 +3891,8 @@ static inline void task_tick_mm_cid(struct rq *rq, struct task_struct *curr) { }
 static inline void init_sched_mm_cid(struct task_struct *t) { }
 #endif /* !CONFIG_SCHED_MM_CID */
 
+extern void init_sched_mm(struct task_struct *p);
+
 extern u64 avg_vruntime(struct cfs_rq *cfs_rq);
 extern int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se);
 #ifdef CONFIG_SMP
-- 
2.25.1

[RFC PATCH v4 02/28] sched: Several fixes for cache aware scheduling

[Chen Yu]

1. Fix compile error on percpu allocation.
2. Enqueue to the target CPU rather than the current CPU.
3. NULL LLC sched domain check(Libo Chen).
4. Introduce sched feature SCHED_CACHE to control cache aware scheduling
5. Fix unsigned occupancy initialization to -1.
6. If there is only 1 thread in the process, no need to enable cache
   awareness
7. Add __maybe_unused to __migrate_degrades_locality() to
   avoid compile warnings.
8. Do not enable gcov coverage for task_cache_work() and
   fraction_mm_sched() to avoid softlockup by gcov.
9. Make CONFIG_SCHED_CACHE depending on CONFIG_SMP to
   avoid compile error on non-SMP system like microblaze
   architecture.
10. Do not enable account cache aware statistics in
    account_mm_sched() for non-normal tasks, as it could
    be invoked by RT tasks.(Shrikanth Hegde)
11. Place cpu_epoch related fields in a dedicated cache line
    to avoid interfering with clock_idle* fields.
    (Shrikanth Hegde)

Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 include/linux/mm_types.h |  4 ++--
 init/Kconfig             |  4 ++++
 kernel/sched/fair.c      | 41 +++++++++++++++++++++++++++-------------
 kernel/sched/features.h  |  1 +
 kernel/sched/sched.h     |  2 +-
 5 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index cf26ad8b41ab..41a598a44361 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1450,11 +1450,11 @@ static inline void mm_set_cpus_allowed(struct mm_struct *mm, const struct cpumas
 #endif /* CONFIG_SCHED_MM_CID */
 
 #ifdef CONFIG_SCHED_CACHE
-extern void mm_init_sched(struct mm_struct *mm, struct mm_sched *pcpu_sched);
+void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *pcpu_sched);
 
 static inline int mm_alloc_sched_noprof(struct mm_struct *mm)
 {
-	struct mm_sched *pcpu_sched = alloc_percpu_noprof(struct mm_sched);
+	struct mm_sched __percpu *pcpu_sched = alloc_percpu_noprof(struct mm_sched);
 	if (!pcpu_sched)
 		return -ENOMEM;
 
diff --git a/init/Kconfig b/init/Kconfig
index 27f4012347f9..4bab39a5254c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -950,6 +950,10 @@ config NUMA_BALANCING
 config SCHED_CACHE
 	bool "Cache aware scheduler"
 	default y
+	depends on SMP
+	help
+	  If set, the scheduler will try to aggregate tasks in the same process to
+	  a single LLC if possible.
 
 config NUMA_BALANCING_DEFAULT_ENABLED
 	bool "Automatically enable NUMA aware memory/task placement"
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3897cd7696d..e97ab46509e3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1175,7 +1175,7 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 #define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
 #define EPOCH_OLD	5		/* 50 ms */
 
-void mm_init_sched(struct mm_struct *mm, struct mm_sched *_pcpu_sched)
+void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
 	int i;
@@ -1186,7 +1186,7 @@ void mm_init_sched(struct mm_struct *mm, struct mm_sched *_pcpu_sched)
 
 		pcpu_sched->runtime = 0;
 		pcpu_sched->epoch = epoch = rq->cpu_epoch;
-		pcpu_sched->occ = -1;
+		pcpu_sched->occ = 0;
 	}
 
 	raw_spin_lock_init(&mm->mm_sched_lock);
@@ -1227,7 +1227,7 @@ static inline void __update_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
 	}
 }
 
-static unsigned long fraction_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
+static unsigned long __no_profile fraction_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
 {
 	guard(raw_spinlock_irqsave)(&rq->cpu_epoch_lock);
 
@@ -1248,13 +1248,18 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	struct mm_sched *pcpu_sched;
 	unsigned long epoch;
 
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
+	if (p->sched_class != &fair_sched_class)
+		return;
 	/*
 	 * init_task and kthreads don't be having no mm
 	 */
 	if (!mm || !mm->pcpu_sched)
 		return;
 
-	pcpu_sched = this_cpu_ptr(p->mm->pcpu_sched);
+	pcpu_sched = per_cpu_ptr(p->mm->pcpu_sched, cpu_of(rq));
 
 	scoped_guard (raw_spinlock, &rq->cpu_epoch_lock) {
 		__update_mm_sched(rq, pcpu_sched);
@@ -1264,12 +1269,14 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	}
 
 	/*
-	 * If this task hasn't hit task_cache_work() for a while, invalidate
+	 * If this task hasn't hit task_cache_work() for a while, or it
+	 * has only 1 thread, invalidate
 	 * it's preferred state.
 	 */
-	if (epoch - READ_ONCE(mm->mm_sched_epoch) > EPOCH_OLD) {
+	if (epoch - READ_ONCE(mm->mm_sched_epoch) > EPOCH_OLD ||
+	    get_nr_threads(p) <= 1) {
 		mm->mm_sched_cpu = -1;
-		pcpu_sched->occ = -1;
+		pcpu_sched->occ = 0;
 	}
 }
 
@@ -1278,6 +1285,9 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p)
 	struct callback_head *work = &p->cache_work;
 	struct mm_struct *mm = p->mm;
 
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
 	if (!mm || !mm->pcpu_sched)
 		return;
 
@@ -1286,16 +1296,13 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p)
 
 	guard(raw_spinlock)(&mm->mm_sched_lock);
 
-	if (mm->mm_sched_epoch == rq->cpu_epoch)
-		return;
-
 	if (work->next == work) {
 		task_work_add(p, work, TWA_RESUME);
 		WRITE_ONCE(mm->mm_sched_epoch, rq->cpu_epoch);
 	}
 }
 
-static void task_cache_work(struct callback_head *work)
+static void __no_profile task_cache_work(struct callback_head *work)
 {
 	struct task_struct *p = current;
 	struct mm_struct *mm = p->mm;
@@ -1322,6 +1329,9 @@ static void task_cache_work(struct callback_head *work)
 			unsigned long occ, m_occ = 0, a_occ = 0;
 			int m_cpu = -1, nr = 0, i;
 
+			if (!sd)
+				continue;
+
 			for_each_cpu(i, sched_domain_span(sd)) {
 				occ = fraction_mm_sched(cpu_rq(i),
 							per_cpu_ptr(mm->pcpu_sched, i));
@@ -8815,6 +8825,9 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	struct mm_struct *mm = p->mm;
 	int cpu;
 
+	if (!sched_feat(SCHED_CACHE))
+		return prev_cpu;
+
 	if (!mm || p->nr_cpus_allowed == 1)
 		return prev_cpu;
 
@@ -9569,7 +9582,7 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 		return 0;
 
 #ifdef CONFIG_SCHED_CACHE
-	if (p->mm && p->mm->pcpu_sched) {
+	if (sched_feat(SCHED_CACHE) && p->mm && p->mm->pcpu_sched) {
 		/*
 		 * XXX things like Skylake have non-inclusive L3 and might not
 		 * like this L3 centric view. What to do about L2 stickyness ?
@@ -9647,7 +9660,9 @@ static long migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 }
 
 #else
-static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle)
+static __maybe_unused long __migrate_degrades_locality(struct task_struct *p,
+						       int src_cpu, int dst_cpu,
+						       bool idle)
 {
 	return 0;
 }
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 3c12d9f93331..d2af7bfd36bf 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -87,6 +87,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
  */
 SCHED_FEAT(SIS_UTIL, true)
 
+SCHED_FEAT(SCHED_CACHE, true)
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls
  * in a single rq->lock section. Default disabled because the
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 839463027ab0..f4ab45ecca86 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1174,7 +1174,7 @@ struct rq {
 	u64			clock_idle_copy;
 #endif
 #ifdef CONFIG_SCHED_CACHE
-	raw_spinlock_t		cpu_epoch_lock;
+	raw_spinlock_t		cpu_epoch_lock ____cacheline_aligned;
 	u64			cpu_runtime;
 	unsigned long		cpu_epoch;
 	unsigned long		cpu_epoch_next;
-- 
2.25.1

[RFC PATCH v4 03/28] sched: Avoid task migration within its preferred LLC

[Chen Yu]

It was found that when running schbench, there is a
significant amount of in-LLC task migrations, even if
the wakee is woken up on its preferred LLC. This
leads to core-to-core latency and impairs performance.

Inhibit task migration if the wakee is already in its
preferred LLC.

Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e97ab46509e3..00bd0d25bc91 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8835,6 +8835,8 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	if (cpu < 0)
 		return prev_cpu;
 
+	if (cpus_share_cache(cpu, prev_cpu))
+		return prev_cpu;
 
 	if (static_branch_likely(&sched_numa_balancing) &&
 	    __migrate_degrades_locality(p, prev_cpu, cpu, false) > 0) {
-- 
2.25.1

[RFC PATCH v4 04/28] sched: Avoid calculating the cpumask if the system is overloaded

[Chen Yu]

From: K Prateek Nayak <kprateek.nayak@amd.com>

If SIS_UTIL terminates the search for idle CPUs, the result of
cpumask_and() becomes irrelevant. Given that select_idle_cpu()
may now be invoked twice per wake-up within select_idle_sibling()
due to cache-aware wake-ups, this overhead can be observed in
benchmarks such as hackbench.

To conserve additional cycles-particularly in scenarios where
the LLC is frequently targeted and the search aborts because
the LLC is busy - calculate the cpumask only when the system is
not overloaded.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 00bd0d25bc91..a7be5c5ecba3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7940,8 +7940,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 	int i, cpu, idle_cpu = -1, nr = INT_MAX;
 	struct sched_domain_shared *sd_share;
 
-	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
-
 	if (sched_feat(SIS_UTIL)) {
 		sd_share = rcu_dereference(per_cpu(sd_llc_shared, target));
 		if (sd_share) {
@@ -7953,6 +7951,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 		}
 	}
 
+	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+
 	if (static_branch_unlikely(&sched_cluster_active)) {
 		struct sched_group *sg = sd->groups;
 
-- 
2.25.1

[RFC PATCH v4 05/28] sched: Add hysteresis to switch a task's preferred LLC

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Switching a process's preferred LLC generates lots of task
migrations across LLCs. To avoid frequent switches
of home LLC, implement the following policy:

1. Require a 2x occ change threshold to switch preferred LLC
2. Don't discard preferred LLC for a task

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a7be5c5ecba3..9e3c6f0eb934 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1175,6 +1175,14 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 #define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
 #define EPOCH_OLD	5		/* 50 ms */
 
+static int llc_id(int cpu)
+{
+	if (cpu < 0)
+		return -1;
+
+	return per_cpu(sd_llc_id, cpu);
+}
+
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
@@ -1307,6 +1315,7 @@ static void __no_profile task_cache_work(struct callback_head *work)
 	struct task_struct *p = current;
 	struct mm_struct *mm = p->mm;
 	unsigned long m_a_occ = 0;
+	unsigned long last_m_a_occ = 0;
 	int cpu, m_a_cpu = -1;
 	cpumask_var_t cpus;
 
@@ -1345,11 +1354,13 @@ static void __no_profile task_cache_work(struct callback_head *work)
 					     per_cpu(sd_llc_id, i), occ, m_occ, m_cpu, nr);
 			}
 
-			a_occ /= nr;
+			// a_occ /= nr;
 			if (a_occ > m_a_occ) {
 				m_a_occ = a_occ;
 				m_a_cpu = m_cpu;
 			}
+			if (llc_id(cpu) == llc_id(mm->mm_sched_cpu))
+				last_m_a_occ = a_occ;
 
 			trace_printk("(%d) a_occ: %ld m_a_occ: %ld\n",
 				     per_cpu(sd_llc_id, cpu), a_occ, m_a_occ);
@@ -1363,13 +1374,10 @@ static void __no_profile task_cache_work(struct callback_head *work)
 		}
 	}
 
-	/*
-	 * If the max average cache occupancy is 'small' we don't care.
-	 */
-	if (m_a_occ < (NICE_0_LOAD >> EPOCH_OLD))
-		m_a_cpu = -1;
-
-	mm->mm_sched_cpu = m_a_cpu;
+	if (m_a_occ > (2 * last_m_a_occ)) {
+		/* avoid the bouncing of mm_sched_cpu */
+		mm->mm_sched_cpu = m_a_cpu;
+	}
 
 	free_cpumask_var(cpus);
 }
-- 
2.25.1

[RFC PATCH v4 06/28] sched: Save the per LLC utilization for better cache aware scheduling

[Chen Yu]

When a system gets busy and a process's preferred LLC
is saturated by too many threads within this process, there are significant
in-LLC task migrations within its preferred LLC. This leads to migration
latency and degrades performance. Ideally, task aggregation should be
inhibited if the task's preferred LLC is overloaded. This implies that a
metric is needed to indicate whether the LLC is busy.

Store the per-LLC utilization calculated via periodic load
balancing. These statistics will be used in subsequent patches to
determine whether tasks should be aggregated to their preferred LLC.

Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 include/linux/sched/topology.h |  3 ++
 kernel/sched/fair.c            | 53 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 198bb5cc1774..692f8a703b93 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -78,6 +78,9 @@ struct sched_domain_shared {
 	atomic_t	nr_busy_cpus;
 	int		has_idle_cores;
 	int		nr_idle_scan;
+#ifdef CONFIG_SCHED_CACHE
+	unsigned long	util_avg;
+#endif
 };
 
 struct sched_domain {
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9e3c6f0eb934..4f79b7652642 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8828,6 +8828,22 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 #ifdef CONFIG_SCHED_CACHE
 static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle);
 
+/* expected to be protected by rcu_read_lock() */
+static bool get_llc_stats(int cpu, unsigned long *util,
+			  unsigned long *cap)
+{
+	struct sched_domain_shared *sd_share;
+
+	sd_share = rcu_dereference(per_cpu(sd_llc_shared, cpu));
+	if (!sd_share)
+		return false;
+
+	*util = READ_ONCE(sd_share->util_avg);
+	*cap = per_cpu(sd_llc_size, cpu) * SCHED_CAPACITY_SCALE;
+
+	return true;
+}
+
 static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 {
 	struct mm_struct *mm = p->mm;
@@ -10670,6 +10686,42 @@ sched_reduced_capacity(struct rq *rq, struct sched_domain *sd)
 	return check_cpu_capacity(rq, sd);
 }
 
+#ifdef CONFIG_SCHED_CACHE
+/*
+ * Save this sched group's statistic for later use:
+ * The task wakeup and load balance can make better
+ * decision based on these statistics.
+ */
+static void update_sg_if_llc(struct lb_env *env, struct sg_lb_stats *sgs,
+			     struct sched_group *group)
+{
+	/* Find the sched domain that spans this group. */
+	struct sched_domain *sd = env->sd->child;
+	struct sched_domain_shared *sd_share;
+
+	if (!sched_feat(SCHED_CACHE) || env->idle == CPU_NEWLY_IDLE)
+		return;
+
+	/* only care the sched domain that spans 1 LLC */
+	if (!sd || !(sd->flags & SD_SHARE_LLC) ||
+	    !sd->parent || (sd->parent->flags & SD_SHARE_LLC))
+		return;
+
+	sd_share = rcu_dereference(per_cpu(sd_llc_shared,
+				  cpumask_first(sched_group_span(group))));
+	if (!sd_share)
+		return;
+
+	if (likely(READ_ONCE(sd_share->util_avg) != sgs->group_util))
+		WRITE_ONCE(sd_share->util_avg, sgs->group_util);
+}
+#else
+static inline void update_sg_if_llc(struct lb_env *env, struct sg_lb_stats *sgs,
+				    struct sched_group *group)
+{
+}
+#endif
+
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @env: The load balancing environment.
@@ -10759,6 +10811,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 
 	sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs);
 
+	update_sg_if_llc(env, sgs, group);
 	/* Computing avg_load makes sense only when group is overloaded */
 	if (sgs->group_type == group_overloaded)
 		sgs->avg_load = (sgs->group_load * SCHED_CAPACITY_SCALE) /
-- 
2.25.1

[RFC PATCH v4 07/28] sched: Add helper function to decide whether to allow cache aware scheduling

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Cache-aware scheduling is designed to aggregate threads into their
preferred LLC, either via the task wake up path or the load balancing
path. One side effect is that when the preferred LLC is saturated,
more threads will continue to be stacked on it, degrading the workload's
latency. A strategy is needed to prevent this aggregation from going too
far such that the preferred LLC is too overloaded.

Introduce helper function _get_migrate_hint() to implement the
LLC migration policy:

1) A task is aggregated to its preferred LLC if both source/dest LLC
   are not too busy (<50% utilization, tunable), or the preferred
   LLC will not be too out of balanced from the non preferred LLC
   (>20% utilization, tunable, close to imbalance_pct of the LLC
   domain).
2) Allow a task to be moved from the preferred LLC to the
   non-preferred one if the non-preferred LLC will not be too out
   of balanced from the preferred prompting an aggregation task
   migration later.  We are still experimenting with the aggregation
   and migration policy. Some other possibilities are policy based
   on LLC's load or average number of tasks running.  Those could
   be tried out by tweaking _get_migrate_hint().

The function _get_migrate_hint() returns migration suggestions for
the upper-level functions.

Aggregation will tend to make utilization on the preferred LLC to
be more than the non-preferred one. Parameter "sysctl_llc_aggr_imb"
is the imbalance allowed. If it is set to 0, as long as the preferred
LLC is not utilized more than the source LLC, we could still aggregate
towards the preferred LLC and a preference could still be there.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/debug.c |   4 ++
 kernel/sched/fair.c  | 110 ++++++++++++++++++++++++++++++++++++++++++-
 kernel/sched/sched.h |   5 ++
 3 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 557246880a7e..682fd91a42a0 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -532,6 +532,10 @@ static __init int sched_init_debug(void)
 	debugfs_create_u32("hot_threshold_ms", 0644, numa, &sysctl_numa_balancing_hot_threshold);
 #endif
 
+#ifdef CONFIG_SCHED_CACHE
+	debugfs_create_u32("llc_aggr_cap", 0644, debugfs_sched, &sysctl_llc_aggr_cap);
+	debugfs_create_u32("llc_aggr_imb", 0644, debugfs_sched, &sysctl_llc_aggr_imb);
+#endif
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
 
 	debugfs_fair_server_init();
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4f79b7652642..3128dbcf0a36 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8826,7 +8826,39 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 }
 
 #ifdef CONFIG_SCHED_CACHE
-static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle);
+static long __migrate_degrades_locality(struct task_struct *p,
+					int src_cpu, int dst_cpu,
+					bool idle);
+__read_mostly unsigned int sysctl_llc_aggr_cap       = 50;
+__read_mostly unsigned int sysctl_llc_aggr_imb       = 20;
+
+/*
+ * The margin used when comparing LLC utilization with CPU capacity.
+ * Parameter sysctl_llc_aggr_cap determines the LLC load level where
+ * active LLC aggregation is done.
+ * Derived from fits_capacity().
+ *
+ * (default: ~50%)
+ */
+#define fits_llc_capacity(util, max)	\
+	((util) * 100 < (max) * sysctl_llc_aggr_cap)
+
+/*
+ * The margin used when comparing utilization.
+ * is 'util1' noticeably greater than 'util2'
+ * Derived from capacity_greater().
+ * Bias is in perentage.
+ */
+/* Allows dst util to be bigger than src util by up to bias percent */
+#define util_greater(util1, util2) \
+	((util1) * 100 > (util2) * (100 + sysctl_llc_aggr_imb))
+
+enum llc_mig_hint {
+	mig_allow = 0,
+	mig_ignore,
+	mig_forbid
+};
+
 
 /* expected to be protected by rcu_read_lock() */
 static bool get_llc_stats(int cpu, unsigned long *util,
@@ -8844,6 +8876,82 @@ static bool get_llc_stats(int cpu, unsigned long *util,
 	return true;
 }
 
+static enum llc_mig_hint _get_migrate_hint(int src_cpu, int dst_cpu,
+					   unsigned long tsk_util,
+					   bool to_pref)
+{
+	unsigned long src_util, dst_util, src_cap, dst_cap;
+
+	if (cpus_share_cache(src_cpu, dst_cpu))
+		return mig_allow;
+
+	if (!get_llc_stats(src_cpu, &src_util, &src_cap) ||
+	    !get_llc_stats(dst_cpu, &dst_util, &dst_cap))
+		return mig_ignore;
+
+	if (!fits_llc_capacity(dst_util, dst_cap) &&
+	    !fits_llc_capacity(src_util, src_cap))
+		return mig_ignore;
+
+	src_util = src_util < tsk_util ? 0 : src_util - tsk_util;
+	dst_util = dst_util + tsk_util;
+	if (to_pref) {
+		/*
+		 * sysctl_llc_aggr_imb is the imbalance allowed between
+		 * preferred LLC and non-preferred LLC.
+		 * Don't migrate if we will get preferred LLC too
+		 * heavily loaded and if the dest is much busier
+		 * than the src, in which case migration will
+		 * increase the imbalance too much.
+		 */
+		if (!fits_llc_capacity(dst_util, dst_cap) &&
+		    util_greater(dst_util, src_util))
+			return mig_forbid;
+	} else {
+		/*
+		 * Don't migrate if we will leave preferred LLC
+		 * too idle, or if this migration leads to the
+		 * non-preferred LLC falls within sysctl_aggr_imb percent
+		 * of preferred LLC, leading to migration again
+		 * back to preferred LLC.
+		 */
+		if (fits_llc_capacity(src_util, src_cap) ||
+		    !util_greater(src_util, dst_util))
+			return mig_forbid;
+	}
+	return mig_allow;
+}
+
+/*
+ * Give suggestion when task p is migrated from src_cpu to dst_cpu.
+ */
+static __maybe_unused enum llc_mig_hint get_migrate_hint(int src_cpu, int dst_cpu,
+							 struct task_struct *p)
+{
+	struct mm_struct *mm;
+	int cpu;
+
+	if (cpus_share_cache(src_cpu, dst_cpu))
+		return mig_allow;
+
+	mm = p->mm;
+	if (!mm)
+		return mig_allow;
+
+	cpu = mm->mm_sched_cpu;
+	if (cpu < 0)
+		return mig_allow;
+
+	if (cpus_share_cache(dst_cpu, cpu))
+		return _get_migrate_hint(src_cpu, dst_cpu,
+					 task_util(p), true);
+	else if (cpus_share_cache(src_cpu, cpu))
+		return _get_migrate_hint(src_cpu, dst_cpu,
+					 task_util(p), false);
+	else
+		return mig_allow;
+}
+
 static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 {
 	struct mm_struct *mm = p->mm;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f4ab45ecca86..83552aab74fb 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2844,6 +2844,11 @@ extern unsigned int sysctl_numa_balancing_scan_period_max;
 extern unsigned int sysctl_numa_balancing_scan_size;
 extern unsigned int sysctl_numa_balancing_hot_threshold;
 
+#ifdef CONFIG_SCHED_CACHE
+extern unsigned int sysctl_llc_aggr_cap;
+extern unsigned int sysctl_llc_aggr_imb;
+#endif
+
 #ifdef CONFIG_SCHED_HRTICK
 
 /*
-- 
2.25.1

[RFC PATCH v4 08/28] sched: Set up LLC indexing

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Prepare for indexing arrays that track in each run queue: the number
of tasks preferring current LLC and each of the other LLC.

The reason to introduce LLC index is because the per LLC-scope data
is needed to do cache aware load balancing. However, the native lld_id
is usually the first CPU of that LLC domain, which is not continuous,
which might waste the space if the per LLC-scope data is stored
in an array (in current implementation).

In the future, this LLC index could be removed after
the native llc_id is used as the key to search into xarray based
array.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 include/linux/sched.h   |  3 +++
 kernel/sched/fair.c     | 12 ++++++++++++
 kernel/sched/sched.h    |  2 ++
 kernel/sched/topology.c | 29 +++++++++++++++++++++++++++++
 4 files changed, 46 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 02ff8b8be25b..81d92e8097f5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -809,6 +809,9 @@ struct kmap_ctrl {
 #endif
 };
 
+/* XXX need fix to not use magic number */
+#define MAX_LLC 64
+
 struct task_struct {
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	/*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3128dbcf0a36..f5075d287c51 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1183,6 +1183,18 @@ static int llc_id(int cpu)
 	return per_cpu(sd_llc_id, cpu);
 }
 
+/*
+ * continuous index.
+ * TBD: replace by xarray with key llc_id()
+ */
+static inline int llc_idx(int cpu)
+{
+	if (cpu < 0)
+		return -1;
+
+	return per_cpu(sd_llc_idx, cpu);
+}
+
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 83552aab74fb..c37c74dfce25 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2056,6 +2056,7 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DECLARE_PER_CPU(int, sd_llc_size);
 DECLARE_PER_CPU(int, sd_llc_id);
+DECLARE_PER_CPU(int, sd_llc_idx);
 DECLARE_PER_CPU(int, sd_share_id);
 DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
@@ -2064,6 +2065,7 @@ DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 
 extern struct static_key_false sched_asym_cpucapacity;
 extern struct static_key_false sched_cluster_active;
+extern int max_llcs;
 
 static __always_inline bool sched_asym_cpucap_active(void)
 {
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index b958fe48e020..91a2b7f65fee 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -657,6 +657,7 @@ static void destroy_sched_domains(struct sched_domain *sd)
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DEFINE_PER_CPU(int, sd_llc_size);
 DEFINE_PER_CPU(int, sd_llc_id);
+DEFINE_PER_CPU(int, sd_llc_idx);
 DEFINE_PER_CPU(int, sd_share_id);
 DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
@@ -666,6 +667,25 @@ DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
 DEFINE_STATIC_KEY_FALSE(sched_cluster_active);
 
+int max_llcs = -1;
+
+static void update_llc_idx(int cpu)
+{
+#ifdef CONFIG_SCHED_CACHE
+	int idx = -1, llc_id = -1;
+
+	llc_id = per_cpu(sd_llc_id, cpu);
+	idx = per_cpu(sd_llc_idx, llc_id);
+
+	if (idx < 0) {
+		idx = max_llcs++;
+		BUG_ON(idx > MAX_LLC);
+		per_cpu(sd_llc_idx, llc_id) = idx;
+	}
+	per_cpu(sd_llc_idx, cpu) = idx;
+#endif
+}
+
 static void update_top_cache_domain(int cpu)
 {
 	struct sched_domain_shared *sds = NULL;
@@ -684,6 +704,7 @@ static void update_top_cache_domain(int cpu)
 	per_cpu(sd_llc_size, cpu) = size;
 	per_cpu(sd_llc_id, cpu) = id;
 	rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds);
+	update_llc_idx(cpu);
 
 	sd = lowest_flag_domain(cpu, SD_CLUSTER);
 	if (sd)
@@ -2456,6 +2477,14 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 	bool has_asym = false;
 	bool has_cluster = false;
 
+#ifdef CONFIG_SCHED_CACHE
+	if (max_llcs < 0) {
+		for_each_possible_cpu(i)
+			per_cpu(sd_llc_idx, i) = -1;
+		max_llcs = 0;
+	}
+#endif
+
 	if (WARN_ON(cpumask_empty(cpu_map)))
 		goto error;
 
-- 
2.25.1

[RFC PATCH v4 09/28] sched: Introduce task preferred LLC field

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

With cache aware scheduling enabled, each process is assigned
a preferred LLC id, which will be used to quickly identify
the LLC domain this thread prefers to run. This is similar to
numa_preferred_nid for NUMA balance.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 include/linux/sched.h | 1 +
 init/init_task.c      | 3 +++
 kernel/sched/fair.c   | 7 +++++++
 3 files changed, 11 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 81d92e8097f5..ac4973728c3e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1408,6 +1408,7 @@ struct task_struct {
 
 #ifdef CONFIG_SCHED_CACHE
 	struct callback_head		cache_work;
+	int				preferred_llc;
 #endif
 
 #ifdef CONFIG_RSEQ
diff --git a/init/init_task.c b/init/init_task.c
index e557f622bd90..5fffbe766f57 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -188,6 +188,9 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 	.numa_group	= NULL,
 	.numa_faults	= NULL,
 #endif
+#ifdef CONFIG_SCHED_CACHE
+	.preferred_llc  = -1,
+#endif
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 	.kasan_depth	= 1,
 #endif
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f5075d287c51..94ad84ba19e1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1267,6 +1267,7 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	struct mm_struct *mm = p->mm;
 	struct mm_sched *pcpu_sched;
 	unsigned long epoch;
+	int mm_sched_llc = -1;
 
 	if (!sched_feat(SCHED_CACHE))
 		return;
@@ -1298,6 +1299,12 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 		mm->mm_sched_cpu = -1;
 		pcpu_sched->occ = 0;
 	}
+
+	if (mm->mm_sched_cpu != -1)
+		mm_sched_llc = per_cpu(sd_llc_id, mm->mm_sched_cpu);
+
+	if (p->preferred_llc != mm_sched_llc)
+		p->preferred_llc = mm_sched_llc;
 }
 
 static void task_tick_cache(struct rq *rq, struct task_struct *p)
-- 
2.25.1

[RFC PATCH v4 10/28] sched: Calculate the number of tasks that have LLC preference on a runqueue

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Track for each run queue, the number of tasks that have a LLC preference
and how many of those tasks are running in its preferred LLC.  This is
similar to nr_numa_running and nr_preferred_running for NUMA balance,
and will be used by the cache-aware load balancing in subsequent patches.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/core.c  | 12 +++++++++++
 kernel/sched/fair.c  | 51 +++++++++++++++++++++++++++++++++++++++++++-
 kernel/sched/sched.h |  7 ++++++
 3 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a5fb3057b1c4..a97a8039ce91 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -499,6 +499,18 @@ void __trace_set_current_state(int state_value)
 }
 EXPORT_SYMBOL(__trace_set_current_state);
 
+#ifdef CONFIG_SMP
+int task_llc(const struct task_struct *p)
+{
+	return per_cpu(sd_llc_id, task_cpu(p));
+}
+#else
+int task_llc(const struct task_struct *p)
+{
+	return 0;
+}
+#endif
+
 /*
  * Serialization rules:
  *
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 94ad84ba19e1..f964d5a44fcc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1195,6 +1195,24 @@ static inline int llc_idx(int cpu)
 	return per_cpu(sd_llc_idx, cpu);
 }
 
+static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
+{
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
+	rq->nr_llc_running += (p->preferred_llc != -1);
+	rq->nr_pref_llc_running += (p->preferred_llc == task_llc(p));
+}
+
+static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
+{
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
+	rq->nr_llc_running -= (p->preferred_llc != -1);
+	rq->nr_pref_llc_running -= (p->preferred_llc == task_llc(p));
+}
+
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
@@ -1303,8 +1321,11 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	if (mm->mm_sched_cpu != -1)
 		mm_sched_llc = per_cpu(sd_llc_id, mm->mm_sched_cpu);
 
-	if (p->preferred_llc != mm_sched_llc)
+	if (p->preferred_llc != mm_sched_llc) {
+		account_llc_dequeue(rq, p);
 		p->preferred_llc = mm_sched_llc;
+		account_llc_enqueue(rq, p);
+	}
 }
 
 static void task_tick_cache(struct rq *rq, struct task_struct *p)
@@ -1408,6 +1429,17 @@ void init_sched_mm(struct task_struct *p)
 	work->next = work;
 }
 
+void reset_llc_stats(struct rq *rq)
+{
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
+	if (rq->nr_llc_running)
+		rq->nr_llc_running = 0;
+
+	rq->nr_pref_llc_running = 0;
+}
+
 #else
 
 static inline void account_mm_sched(struct rq *rq, struct task_struct *p,
@@ -1418,6 +1450,17 @@ void init_sched_mm(struct task_struct *p) { }
 
 static void task_tick_cache(struct rq *rq, struct task_struct *p) { }
 
+static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
+{
+}
+
+static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
+{
+}
+
+void reset_llc_stats(struct rq *rq)
+{
+}
 #endif
 
 static inline
@@ -3957,6 +4000,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		struct rq *rq = rq_of(cfs_rq);
 
 		account_numa_enqueue(rq, task_of(se));
+		account_llc_enqueue(rq, task_of(se));
 		list_add(&se->group_node, &rq->cfs_tasks);
 	}
 #endif
@@ -3970,10 +4014,15 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 #ifdef CONFIG_SMP
 	if (entity_is_task(se)) {
 		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
+		account_llc_dequeue(rq_of(cfs_rq), task_of(se));
 		list_del_init(&se->group_node);
 	}
 #endif
 	cfs_rq->nr_queued--;
+
+	/* safeguard? */
+	if (!parent_entity(se) && !cfs_rq->nr_queued)
+		reset_llc_stats(rq_of(cfs_rq));
 }
 
 /*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c37c74dfce25..8026e2c66e9f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1106,6 +1106,10 @@ struct rq {
 	unsigned int		nr_preferred_running;
 	unsigned int		numa_migrate_on;
 #endif
+#ifdef CONFIG_SCHED_CACHE
+	unsigned int		nr_pref_llc_running;
+	unsigned int		nr_llc_running;
+#endif
 #ifdef CONFIG_NO_HZ_COMMON
 #ifdef CONFIG_SMP
 	unsigned long		last_blocked_load_update_tick;
@@ -1967,6 +1971,9 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
 
 #endif /* !CONFIG_NUMA_BALANCING */
 
+void reset_llc_stats(struct rq *rq);
+int task_llc(const struct task_struct *p);
+
 #ifdef CONFIG_SMP
 
 static inline void
-- 
2.25.1

[RFC PATCH v4 11/28] sched: Introduce per runqueue task LLC preference counter

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Each runqueue is assigned a static array, where each element indicates
the number of tasks preferring a particular LLC mapped to the
array index.

For example, rq->nr_pref_llc[3] = 2 signifies that there are 2 tasks on
this runqueue which prefer to run within LLC3 (indexed from 0 to MAX_LLC
across the entire system). With this information, the load balancer can
make better decisions to select the busiest runqueue and migrate tasks
to their preferred LLC domains.

Note: The static array could be converted to an xarray in the future.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c  | 42 ++++++++++++++++++++++++++++++++++++++++--
 kernel/sched/sched.h |  1 +
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f964d5a44fcc..cfae71ee870b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1195,22 +1195,51 @@ static inline int llc_idx(int cpu)
 	return per_cpu(sd_llc_idx, cpu);
 }
 
+static inline int pref_llc_idx(struct task_struct *p)
+{
+	return llc_idx(p->preferred_llc);
+}
+
 static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
 {
+	int pref_llc;
+
 	if (!sched_feat(SCHED_CACHE))
 		return;
 
 	rq->nr_llc_running += (p->preferred_llc != -1);
 	rq->nr_pref_llc_running += (p->preferred_llc == task_llc(p));
+
+	if (p->preferred_llc < 0)
+		return;
+
+	pref_llc = pref_llc_idx(p);
+	if (pref_llc < 0)
+		return;
+
+	++rq->nr_pref_llc[pref_llc];
 }
 
 static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
 {
+	int pref_llc;
+
 	if (!sched_feat(SCHED_CACHE))
 		return;
 
 	rq->nr_llc_running -= (p->preferred_llc != -1);
 	rq->nr_pref_llc_running -= (p->preferred_llc == task_llc(p));
+
+	if (p->preferred_llc < 0)
+		return;
+
+	pref_llc = pref_llc_idx(p);
+	if (pref_llc < 0)
+		return;
+
+	/* avoid negative counter */
+	if (rq->nr_pref_llc[pref_llc] > 0)
+		--rq->nr_pref_llc[pref_llc];
 }
 
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
@@ -1279,6 +1308,8 @@ static unsigned long __no_profile fraction_mm_sched(struct rq *rq, struct mm_sch
 	return div64_u64(NICE_0_LOAD * pcpu_sched->runtime, rq->cpu_runtime + 1);
 }
 
+static unsigned int task_running_on_cpu(int cpu, struct task_struct *p);
+
 static inline
 void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 {
@@ -1321,7 +1352,9 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	if (mm->mm_sched_cpu != -1)
 		mm_sched_llc = per_cpu(sd_llc_id, mm->mm_sched_cpu);
 
-	if (p->preferred_llc != mm_sched_llc) {
+	/* task not on rq accounted later in account_entity_enqueue() */
+	if (task_running_on_cpu(rq->cpu, p) &&
+	    p->preferred_llc != mm_sched_llc) {
 		account_llc_dequeue(rq, p);
 		p->preferred_llc = mm_sched_llc;
 		account_llc_enqueue(rq, p);
@@ -1431,11 +1464,16 @@ void init_sched_mm(struct task_struct *p)
 
 void reset_llc_stats(struct rq *rq)
 {
+	int i;
+
 	if (!sched_feat(SCHED_CACHE))
 		return;
 
-	if (rq->nr_llc_running)
+	if (rq->nr_llc_running) {
+		for (i = 0; i < MAX_LLC; ++i)
+			rq->nr_pref_llc[i] = 0;
 		rq->nr_llc_running = 0;
+	}
 
 	rq->nr_pref_llc_running = 0;
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 8026e2c66e9f..4464b92767ad 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1109,6 +1109,7 @@ struct rq {
 #ifdef CONFIG_SCHED_CACHE
 	unsigned int		nr_pref_llc_running;
 	unsigned int		nr_llc_running;
+	unsigned int		nr_pref_llc[MAX_LLC];
 #endif
 #ifdef CONFIG_NO_HZ_COMMON
 #ifdef CONFIG_SMP
-- 
2.25.1

[RFC PATCH v4 12/28] sched: Calculate the total number of preferred LLC tasks during load balance

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

During load balancing between LLCs, gather the number of tasks
on each runqueue of a source LLC.

For example, consider a system with 4 sched groups LLC0, LLC1,
..., LLC3. We are balancing towards LLC3 and LLC0 has 3 tasks
preferring LLC3, LLC1 has 2 tasks preferring LLC3 and LLC2 has
1 task preferring LLC3. LLC0 with most tasks preferring LLC3
will be chosen as the busiest LLC to pick the tasks from.

The number of tasks preferring the destination LLC are gathered
from each run queue for a source LLC.

For example, consider the sched_group LLC0 with two CPUs, CPU0
and CPU1. On CPU0, 2 tasks prefer to run on LLC3, and on CPU1,
one task prefers LLC3. The total number of tasks preferring
LLC3 in LLC0 is 2 + 1 = 3.

These statistics enable the load balancer to select tasks from
a sched_group that best aligns tasks with their preferred LLCs.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cfae71ee870b..f1697658c3b8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10496,6 +10496,9 @@ struct sg_lb_stats {
 	unsigned int nr_numa_running;
 	unsigned int nr_preferred_running;
 #endif
+#ifdef CONFIG_SCHED_CACHE
+	unsigned int nr_pref_llc[MAX_LLC];
+#endif
 };
 
 /*
@@ -10974,6 +10977,14 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		if (cpu_overutilized(i))
 			*sg_overutilized = 1;
 
+#ifdef CONFIG_SCHED_CACHE
+		if (sched_feat(SCHED_CACHE)) {
+			int j;
+
+			for (j = 0; j < max_llcs; ++j)
+				sgs->nr_pref_llc[j] += rq->nr_pref_llc[j];
+		}
+#endif
 		/*
 		 * No need to call idle_cpu() if nr_running is not 0
 		 */
-- 
2.25.1

[RFC PATCH v4 13/28] sched: Tag the sched group as llc_balance if it has tasks prefer other LLC

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

During load balancing between LLCs, check whether there are tasks
preferring the destination LLC. If so, balance those tasks to the
destination LLC first.

Tag the sched_group that has tasks preferring to run on other LLCs
(non-local) with the group_llc_balance flag. This way, the load
balancer will later attempt to pull/push these tasks to their
preferred LLCs.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f1697658c3b8..30ebc7d1b999 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10491,6 +10491,7 @@ struct sg_lb_stats {
 	enum group_type group_type;
 	unsigned int group_asym_packing;	/* Tasks should be moved to preferred CPU */
 	unsigned int group_smt_balance;		/* Task on busy SMT be moved */
+	unsigned int group_llc_balance;		/* Tasks should be moved to preferred LLC */
 	unsigned long group_misfit_task_load;	/* A CPU has a task too big for its capacity */
 #ifdef CONFIG_NUMA_BALANCING
 	unsigned int nr_numa_running;
@@ -10855,6 +10856,43 @@ static inline bool smt_balance(struct lb_env *env, struct sg_lb_stats *sgs,
 	return false;
 }
 
+/*
+ * Do LLC balance on sched group that contains LLC, and have tasks preferring
+ * to run on LLC in idle dst_cpu.
+ */
+#ifdef CONFIG_SCHED_CACHE
+static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
+			       struct sched_group *group)
+{
+	struct sched_domain *child = env->sd->child;
+	int llc;
+
+	if (!sched_feat(SCHED_CACHE))
+		return false;
+
+	if (env->sd->flags & SD_SHARE_LLC)
+		return false;
+
+	/* only care about task migration among LLCs */
+	if (child && !(child->flags & SD_SHARE_LLC))
+		return false;
+
+	llc = llc_idx(env->dst_cpu);
+	if (sgs->nr_pref_llc[llc] > 0 &&
+	    _get_migrate_hint(env->src_cpu, env->dst_cpu,
+			      0, true) == mig_allow)
+		return true;
+
+	return false;
+}
+#else
+static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
+			       struct sched_group *group)
+{
+	return false;
+}
+#endif
+
 static inline long sibling_imbalance(struct lb_env *env,
 				    struct sd_lb_stats *sds,
 				    struct sg_lb_stats *busiest,
@@ -11037,6 +11075,11 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 	sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs);
 
 	update_sg_if_llc(env, sgs, group);
+
+	/* Check for tasks in this group can be moved to their preferred LLC */
+	if (!local_group && llc_balance(env, sgs, group))
+		sgs->group_llc_balance = 1;
+
 	/* Computing avg_load makes sense only when group is overloaded */
 	if (sgs->group_type == group_overloaded)
 		sgs->avg_load = (sgs->group_load * SCHED_CAPACITY_SCALE) /
-- 
2.25.1

[RFC PATCH v4 14/28] sched: Introduce update_llc_busiest() to deal with groups having preferred LLC tasks

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

The load balancer attempts to identify the busiest sched_group with
the highest load and migrates some tasks to a less busy sched_group
to distribute the load across different CPUs.

When cache-aware scheduling is enabled, the busiest sched_group is
defined as the one with the highest number of tasks preferring to run
on the destination LLC. If the busiest group has llc_balance tag,
the cache aware load balance will be launched.

Introduce the helper function update_llc_busiest() to identify
such sched group with most tasks preferring the destination LLC.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 30ebc7d1b999..b8cc85291351 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10885,12 +10885,36 @@ static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
 
 	return false;
 }
+
+static bool update_llc_busiest(struct lb_env *env,
+			       struct sg_lb_stats *busiest,
+			       struct sg_lb_stats *sgs)
+{
+	int idx;
+
+	/* Only the candidate with llc_balance need to be taken care of */
+	if (!sgs->group_llc_balance)
+		return false;
+
+	/*
+	 * There are more tasks that want to run on dst_cpu's LLC.
+	 */
+	idx = llc_idx(env->dst_cpu);
+	return sgs->nr_pref_llc[idx] > busiest->nr_pref_llc[idx];
+}
 #else
 static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
 			       struct sched_group *group)
 {
 	return false;
 }
+
+static bool update_llc_busiest(struct lb_env *env,
+			       struct sg_lb_stats *busiest,
+			       struct sg_lb_stats *sgs)
+{
+	return false;
+}
 #endif
 
 static inline long sibling_imbalance(struct lb_env *env,
@@ -11122,6 +11146,14 @@ static bool update_sd_pick_busiest(struct lb_env *env,
 	     sds->local_stat.group_type != group_has_spare))
 		return false;
 
+	/* deal with prefer LLC load balance, if failed, fall into normal load balance */
+	if (update_llc_busiest(env, busiest, sgs))
+		return true;
+
+	/* if there is already a busy group, skip the normal load balance */
+	if (busiest->group_llc_balance)
+		return false;
+
 	if (sgs->group_type > busiest->group_type)
 		return true;
 
@@ -12029,9 +12061,11 @@ static struct sched_group *sched_balance_find_src_group(struct lb_env *env)
 	/*
 	 * Try to move all excess tasks to a sibling domain of the busiest
 	 * group's child domain.
+	 * Also do so if we can move some tasks that prefer the local LLC.
 	 */
 	if (sds.prefer_sibling && local->group_type == group_has_spare &&
-	    sibling_imbalance(env, &sds, busiest, local) > 1)
+	    (busiest->group_llc_balance ||
+	    sibling_imbalance(env, &sds, busiest, local) > 1))
 		goto force_balance;
 
 	if (busiest->group_type != group_overloaded) {
-- 
2.25.1

[RFC PATCH v4 15/28] sched: Introduce a new migration_type to track the preferred LLC load balance

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Introduce a new migration type named migrate_llc_task to facilitate
cache-aware load balancing.

After the busiest sched_group is identified as the one that needs
migration due to having most tasks preferring destination LLC, tag the
migration type as the newly introduced migrate_llc_task. During load
balancing, each runqueue within the busiest preferred-LLC sched_group
is checked, and the runqueue with the highest number of tasks preferring
to run on the destination CPU is chosen as the busiest runqueue.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b8cc85291351..a301b56dd2b4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9746,7 +9746,8 @@ enum migration_type {
 	migrate_load = 0,
 	migrate_util,
 	migrate_task,
-	migrate_misfit
+	migrate_misfit,
+	migrate_llc_task
 };
 
 #define LBF_ALL_PINNED	0x01
@@ -10180,6 +10181,15 @@ static int detach_tasks(struct lb_env *env)
 			env->imbalance -= util;
 			break;
 
+		case migrate_llc_task:
+			/*
+			 * Since can_migrate_task() succeed, when we reach here, it means that p
+			 * can be migrated even if dst_cpu is not p's preferred_llc, because there
+			 * are no idle cores for p to do in-llc load balance.
+			 */
+			env->imbalance--;
+			break;
+
 		case migrate_task:
 			env->imbalance--;
 			break;
@@ -11817,6 +11827,15 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		return;
 	}
 
+#ifdef CONFIG_SCHED_CACHE
+	if (busiest->group_llc_balance) {
+		/* Move a task that prefer local LLC */
+		env->migration_type = migrate_llc_task;
+		env->imbalance = 1;
+		return;
+	}
+#endif
+
 	if (busiest->group_type == group_imbalanced) {
 		/*
 		 * In the group_imb case we cannot rely on group-wide averages
@@ -12125,6 +12144,10 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
 	struct rq *busiest = NULL, *rq;
 	unsigned long busiest_util = 0, busiest_load = 0, busiest_capacity = 1;
 	unsigned int busiest_nr = 0;
+#ifdef CONFIG_SCHED_CACHE
+	unsigned int busiest_pref_llc = 0;
+	int dst_llc;
+#endif
 	int i;
 
 	for_each_cpu_and(i, sched_group_span(group), env->cpus) {
@@ -12233,6 +12256,16 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
 			}
 			break;
 
+		case migrate_llc_task:
+#ifdef CONFIG_SCHED_CACHE
+			dst_llc = llc_idx(env->dst_cpu);
+			if (!cpus_share_cache(env->dst_cpu, rq->cpu) &&
+			    busiest_pref_llc < rq->nr_pref_llc[dst_llc]) {
+				busiest_pref_llc = rq->nr_pref_llc[dst_llc];
+				busiest = rq;
+			}
+#endif
+			break;
 		case migrate_task:
 			if (busiest_nr < nr_running) {
 				busiest_nr = nr_running;
@@ -12415,6 +12448,8 @@ static void update_lb_imbalance_stat(struct lb_env *env, struct sched_domain *sd
 	case migrate_misfit:
 		__schedstat_add(sd->lb_imbalance_misfit[idle], env->imbalance);
 		break;
+	case migrate_llc_task:
+		break;
 	}
 }
 
-- 
2.25.1

[RFC PATCH v4 16/28] sched: Consider LLC locality for active balance

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

If busiest run queue has only one task, active balance is enlisted
to actually move the task.  However, before moving the task,
we should consider whether we are moving the task from its preferred
LLC.

Don't move the single running task in a run queue to another LLC, if
we are moving it from its desired LLC, or moving it will cause too much
imbalance between the LLCs.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 51 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a301b56dd2b4..592a4034e760 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12332,10 +12332,43 @@ imbalanced_active_balance(struct lb_env *env)
 	return 0;
 }
 
+#ifdef CONFIG_SCHED_CACHE
+static inline bool
+break_llc_locality(struct lb_env *env)
+{
+	if (!sched_feat(SCHED_CACHE))
+		return 0;
+
+	if (cpus_share_cache(env->src_cpu, env->dst_cpu))
+		return 0;
+	/*
+	 * All tasks want to stay put. Move only if LLC is
+	 * heavily loaded or don't pull a task from its
+	 * preferred CPU if it is the only one running.
+	 */
+	if (env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable &&
+	    (env->src_rq->nr_running <= 1 ||
+	    _get_migrate_hint(env->src_cpu, env->dst_cpu,
+			      0, false) == mig_forbid))
+		return 1;
+
+	return 0;
+}
+#else
+static inline bool
+break_llc_locality(struct lb_env *env)
+{
+	return 0;
+}
+#endif
+
 static int need_active_balance(struct lb_env *env)
 {
 	struct sched_domain *sd = env->sd;
 
+	if (break_llc_locality(env))
+		return 0;
+
 	if (asym_active_balance(env))
 		return 1;
 
@@ -12355,7 +12388,8 @@ static int need_active_balance(struct lb_env *env)
 			return 1;
 	}
 
-	if (env->migration_type == migrate_misfit)
+	if (env->migration_type == migrate_misfit ||
+	    env->migration_type == migrate_llc_task)
 		return 1;
 
 	return 0;
@@ -12800,9 +12834,20 @@ static int active_load_balance_cpu_stop(void *data)
 		goto out_unlock;
 
 	/* Is there any task to move? */
-	if (busiest_rq->nr_running <= 1)
-		goto out_unlock;
+	if (busiest_rq->nr_running <= 1) {
+#ifdef CONFIG_SCHED_CACHE
+		int llc = llc_idx(target_cpu);
 
+		if (!sched_feat(SCHED_CACHE))
+			goto out_unlock;
+
+		if (llc < 0)
+			goto out_unlock;
+		/* don't migrate if task does not prefer target */
+		if (busiest_rq->nr_pref_llc[llc] < 1)
+#endif
+			goto out_unlock;
+	}
 	/*
 	 * This condition is "impossible", if it occurs
 	 * we need to fix it. Originally reported by
-- 
2.25.1

[RFC PATCH v4 17/28] sched: Consider LLC preference when picking tasks from busiest queue

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

When picking tasks from busiest queue for load balance, we currently
do not consider LLC preference.

Order the task in the busiest queue such that we picked the tasks in the
following order:
	1. tasks that prefer dst cpu's LLC
	2. tasks that have no preference in LLC
	3. tasks that prefer LLC other than the ones they are on
	4. tasks that prefer the LLC that they are currently on

This will allow tasks better chances to wind up in its preferred LLC.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 66 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 65 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 592a4034e760..8d5792b9e658 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10093,6 +10093,68 @@ static struct task_struct *detach_one_task(struct lb_env *env)
 	return NULL;
 }
 
+#ifdef CONFIG_SCHED_CACHE
+/*
+ * Prepare lists to detach tasks in the following order:
+ * 1. tasks that prefer dst cpu's LLC
+ * 2. tasks that have no preference in LLC
+ * 3. tasks that prefer LLC other than the ones they are on
+ * 4. tasks that prefer the LLC that they are currently on.
+ */
+static struct list_head
+*order_tasks_by_llc(struct lb_env *env, struct list_head *tasks)
+{
+	struct task_struct *p;
+	LIST_HEAD(pref_old_llc);
+	LIST_HEAD(pref_new_llc);
+	LIST_HEAD(no_pref_llc);
+	LIST_HEAD(pref_other_llc);
+
+	if (!sched_feat(SCHED_CACHE))
+		return tasks;
+
+	if (cpus_share_cache(env->dst_cpu, env->src_cpu))
+		return tasks;
+
+	while (!list_empty(tasks)) {
+		p = list_last_entry(tasks, struct task_struct, se.group_node);
+
+		if (p->preferred_llc == llc_id(env->dst_cpu)) {
+			list_move(&p->se.group_node, &pref_new_llc);
+			continue;
+		}
+
+		if (p->preferred_llc == llc_id(env->src_cpu)) {
+			list_move(&p->se.group_node, &pref_old_llc);
+			continue;
+		}
+
+		if (p->preferred_llc == -1) {
+			list_move(&p->se.group_node, &no_pref_llc);
+			continue;
+		}
+
+		list_move(&p->se.group_node, &pref_other_llc);
+	}
+
+	/*
+	 * We detach tasks from list tail in detach tasks.  Put tasks
+	 * to be chosen first at end of list.
+	 */
+	list_splice(&pref_new_llc, tasks);
+	list_splice(&no_pref_llc, tasks);
+	list_splice(&pref_other_llc, tasks);
+	list_splice(&pref_old_llc, tasks);
+	return tasks;
+}
+#else
+static inline struct list_head
+*order_tasks_by_llc(struct lb_env *env, struct list_head *tasks)
+{
+	return tasks;
+}
+#endif
+
 /*
  * detach_tasks() -- tries to detach up to imbalance load/util/tasks from
  * busiest_rq, as part of a balancing operation within domain "sd".
@@ -10101,7 +10163,7 @@ static struct task_struct *detach_one_task(struct lb_env *env)
  */
 static int detach_tasks(struct lb_env *env)
 {
-	struct list_head *tasks = &env->src_rq->cfs_tasks;
+	struct list_head *tasks;
 	unsigned long util, load;
 	struct task_struct *p;
 	int detached = 0;
@@ -10120,6 +10182,8 @@ static int detach_tasks(struct lb_env *env)
 	if (env->imbalance <= 0)
 		return 0;
 
+	tasks = order_tasks_by_llc(env, &env->src_rq->cfs_tasks);
+
 	while (!list_empty(tasks)) {
 		/*
 		 * We don't want to steal all, otherwise we may be treated likewise,
-- 
2.25.1

[RFC PATCH v4 18/28] sched: Do not migrate task if it is moving out of its preferred LLC

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

In the final step of task migration during load balancing,
can_migrate_task() is used to determine whether a task can
be moved to the destination. If the task has an LLC preference,
consider this preference when moving it out of its preferred LLC.
With this check in place, there is no need to retain the task's
cache-hot CPU check in task_hot(); remove it accordingly.

Besides, add more checks in detach_tasks() to avoid choosing
tasks that prefer their current LLC.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8d5792b9e658..22b7a7fe538e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9822,17 +9822,6 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 	if (sysctl_sched_migration_cost == 0)
 		return 0;
 
-#ifdef CONFIG_SCHED_CACHE
-	if (sched_feat(SCHED_CACHE) && p->mm && p->mm->pcpu_sched) {
-		/*
-		 * XXX things like Skylake have non-inclusive L3 and might not
-		 * like this L3 centric view. What to do about L2 stickyness ?
-		 */
-		return per_cpu_ptr(p->mm->pcpu_sched, env->src_cpu)->occ >
-		       per_cpu_ptr(p->mm->pcpu_sched, env->dst_cpu)->occ;
-	}
-#endif
-
 	delta = rq_clock_task(env->src_rq) - p->se.exec_start;
 
 	return delta < (s64)sysctl_sched_migration_cost;
@@ -10029,6 +10018,12 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 	if (env->flags & LBF_ACTIVE_LB)
 		return 1;
 
+#ifdef CONFIG_SCHED_CACHE
+	if (sched_feat(SCHED_CACHE) &&
+	    get_migrate_hint(env->src_cpu, env->dst_cpu, p) == mig_forbid)
+		return 0;
+#endif
+
 	degrades = migrate_degrades_locality(p, env);
 	if (!degrades)
 		hot = task_hot(p, env);
@@ -10289,6 +10284,17 @@ static int detach_tasks(struct lb_env *env)
 		if (env->imbalance <= 0)
 			break;
 
+#ifdef CONFIG_SCHED_CACHE
+		/*
+		 * Don't detach more tasks if remaining tasks want to stay:
+		 * The tasks have already been sorted by order_tasks_by_llc(),
+		 * they are tasks that prefer the current LLC.
+		 */
+		if (sched_feat(SCHED_CACHE) && p->preferred_llc != -1 &&
+		    llc_id(env->src_cpu) == p->preferred_llc)
+			break;
+#endif
+
 		continue;
 next:
 		if (p->sched_task_hot)
-- 
2.25.1

[RFC PATCH v4 19/28] sched: Introduce SCHED_CACHE_LB to control cache aware load balance

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Introduce the SCHED_CACHE_LB sched feature to enable or disable
cache aware load balance in the schduler.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c     | 18 ++++++++++--------
 kernel/sched/features.h |  1 +
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 22b7a7fe538e..9843d4e1d84f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10019,7 +10019,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 		return 1;
 
 #ifdef CONFIG_SCHED_CACHE
-	if (sched_feat(SCHED_CACHE) &&
+	if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB) &&
 	    get_migrate_hint(env->src_cpu, env->dst_cpu, p) == mig_forbid)
 		return 0;
 #endif
@@ -10105,7 +10105,7 @@ static struct list_head
 	LIST_HEAD(no_pref_llc);
 	LIST_HEAD(pref_other_llc);
 
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
 		return tasks;
 
 	if (cpus_share_cache(env->dst_cpu, env->src_cpu))
@@ -10290,7 +10290,8 @@ static int detach_tasks(struct lb_env *env)
 		 * The tasks have already been sorted by order_tasks_by_llc(),
 		 * they are tasks that prefer the current LLC.
 		 */
-		if (sched_feat(SCHED_CACHE) && p->preferred_llc != -1 &&
+		if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB) &&
+		    p->preferred_llc != -1 &&
 		    llc_id(env->src_cpu) == p->preferred_llc)
 			break;
 #endif
@@ -10947,7 +10948,7 @@ static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
 	struct sched_domain *child = env->sd->child;
 	int llc;
 
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
 		return false;
 
 	if (env->sd->flags & SD_SHARE_LLC)
@@ -11058,7 +11059,8 @@ static void update_sg_if_llc(struct lb_env *env, struct sg_lb_stats *sgs,
 	struct sched_domain *sd = env->sd->child;
 	struct sched_domain_shared *sd_share;
 
-	if (!sched_feat(SCHED_CACHE) || env->idle == CPU_NEWLY_IDLE)
+	if (!sched_feat(SCHED_CACHE) || env->idle == CPU_NEWLY_IDLE ||
+	    !sched_feat(SCHED_CACHE_LB))
 		return;
 
 	/* only care the sched domain that spans 1 LLC */
@@ -11120,7 +11122,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 			*sg_overutilized = 1;
 
 #ifdef CONFIG_SCHED_CACHE
-		if (sched_feat(SCHED_CACHE)) {
+		if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB)) {
 			int j;
 
 			for (j = 0; j < max_llcs; ++j)
@@ -12406,7 +12408,7 @@ imbalanced_active_balance(struct lb_env *env)
 static inline bool
 break_llc_locality(struct lb_env *env)
 {
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
 		return 0;
 
 	if (cpus_share_cache(env->src_cpu, env->dst_cpu))
@@ -12908,7 +12910,7 @@ static int active_load_balance_cpu_stop(void *data)
 #ifdef CONFIG_SCHED_CACHE
 		int llc = llc_idx(target_cpu);
 
-		if (!sched_feat(SCHED_CACHE))
+		if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
 			goto out_unlock;
 
 		if (llc < 0)
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index d2af7bfd36bf..11dbd74cd365 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -88,6 +88,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
 SCHED_FEAT(SIS_UTIL, true)
 
 SCHED_FEAT(SCHED_CACHE, true)
+SCHED_FEAT(SCHED_CACHE_LB, true)
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls
  * in a single rq->lock section. Default disabled because the
-- 
2.25.1

[RFC PATCH v4 20/28] sched: Introduce SCHED_CACHE_WAKE to control LLC aggregation on wake up

[Chen Yu]

From: Tim Chen <tim.c.chen@linux.intel.com>

Introduce SCHED_CACHE_WAKE feature to enable or disable cache-aware
wake up. Disable this feature by default because cache-aware wakeup
is overly aggressive in stacking wakees of the same process on the
same LLC, if they are frequently woken up.

The wake ups can be much more frequent than load balances, adding
much overhead when load balance alone for LLC aggregation is sufficient.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c     | 6 +++++-
 kernel/sched/features.h | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9843d4e1d84f..6e61f9e1f628 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9063,7 +9063,7 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	struct mm_struct *mm = p->mm;
 	int cpu;
 
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_WAKE))
 		return prev_cpu;
 
 	if (!mm || p->nr_cpus_allowed == 1)
@@ -9076,6 +9076,10 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	if (cpus_share_cache(cpu, prev_cpu))
 		return prev_cpu;
 
+	if (_get_migrate_hint(prev_cpu, cpu,
+			      task_util(p), true) == mig_forbid)
+		return prev_cpu;
+
 	if (static_branch_likely(&sched_numa_balancing) &&
 	    __migrate_degrades_locality(p, prev_cpu, cpu, false) > 0) {
 		/*
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 11dbd74cd365..44b408cf0dd4 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -89,6 +89,7 @@ SCHED_FEAT(SIS_UTIL, true)
 
 SCHED_FEAT(SCHED_CACHE, true)
 SCHED_FEAT(SCHED_CACHE_LB, true)
+SCHED_FEAT(SCHED_CACHE_WAKE, false)
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls
  * in a single rq->lock section. Default disabled because the
-- 
2.25.1

[RFC PATCH v4 21/28] sched: Introduce a static key to enable cache aware only for multi LLCs

[Chen Yu]

If there are more than one LLCs in the node, the
cache aware scheduling is enabled. Otherwise, the
cache aware scheduling is disabled.

The definition of multiple LLCs in a node is that
every node in the system should have more than one
LLC. For example, if node0, node1, and node2 each
have 4 LLCs, while node3 has 1 LLC (possibly due
to CPU hotplug), cache-aware scheduling should be
disabled.

Suggested-by: Libo Chen <libo.chen@oracle.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 kernel/sched/fair.c     | 31 ++++++++++++++++++++++---------
 kernel/sched/sched.h    |  1 +
 kernel/sched/topology.c | 22 ++++++++++++++++++++--
 3 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6e61f9e1f628..194ec594561b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1175,6 +1175,8 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 #define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
 #define EPOCH_OLD	5		/* 50 ms */
 
+DEFINE_STATIC_KEY_FALSE(sched_cache_present);
+
 static int llc_id(int cpu)
 {
 	if (cpu < 0)
@@ -1318,7 +1320,8 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	unsigned long epoch;
 	int mm_sched_llc = -1;
 
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) ||
+	    !static_branch_likely(&sched_cache_present))
 		return;
 
 	if (p->sched_class != &fair_sched_class)
@@ -1366,7 +1369,8 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p)
 	struct callback_head *work = &p->cache_work;
 	struct mm_struct *mm = p->mm;
 
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) ||
+	    !static_branch_likely(&sched_cache_present))
 		return;
 
 	if (!mm || !mm->pcpu_sched)
@@ -9063,7 +9067,8 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	struct mm_struct *mm = p->mm;
 	int cpu;
 
-	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_WAKE))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_WAKE) ||
+	    !static_branch_likely(&sched_cache_present))
 		return prev_cpu;
 
 	if (!mm || p->nr_cpus_allowed == 1)
@@ -10024,6 +10029,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 
 #ifdef CONFIG_SCHED_CACHE
 	if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB) &&
+	   static_branch_likely(&sched_cache_present) &&
 	    get_migrate_hint(env->src_cpu, env->dst_cpu, p) == mig_forbid)
 		return 0;
 #endif
@@ -10109,7 +10115,8 @@ static struct list_head
 	LIST_HEAD(no_pref_llc);
 	LIST_HEAD(pref_other_llc);
 
-	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB) ||
+	    !static_branch_likely(&sched_cache_present))
 		return tasks;
 
 	if (cpus_share_cache(env->dst_cpu, env->src_cpu))
@@ -10295,6 +10302,7 @@ static int detach_tasks(struct lb_env *env)
 		 * they are tasks that prefer the current LLC.
 		 */
 		if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB) &&
+		    static_branch_likely(&sched_cache_present) &&
 		    p->preferred_llc != -1 &&
 		    llc_id(env->src_cpu) == p->preferred_llc)
 			break;
@@ -10952,7 +10960,8 @@ static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
 	struct sched_domain *child = env->sd->child;
 	int llc;
 
-	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB) ||
+	    !static_branch_likely(&sched_cache_present))
 		return false;
 
 	if (env->sd->flags & SD_SHARE_LLC)
@@ -11064,7 +11073,8 @@ static void update_sg_if_llc(struct lb_env *env, struct sg_lb_stats *sgs,
 	struct sched_domain_shared *sd_share;
 
 	if (!sched_feat(SCHED_CACHE) || env->idle == CPU_NEWLY_IDLE ||
-	    !sched_feat(SCHED_CACHE_LB))
+	    !sched_feat(SCHED_CACHE_LB) ||
+	    !static_branch_likely(&sched_cache_present))
 		return;
 
 	/* only care the sched domain that spans 1 LLC */
@@ -11126,7 +11136,8 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 			*sg_overutilized = 1;
 
 #ifdef CONFIG_SCHED_CACHE
-		if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB)) {
+		if (sched_feat(SCHED_CACHE) && sched_feat(SCHED_CACHE_LB) &&
+		    static_branch_likely(&sched_cache_present)) {
 			int j;
 
 			for (j = 0; j < max_llcs; ++j)
@@ -12412,7 +12423,8 @@ imbalanced_active_balance(struct lb_env *env)
 static inline bool
 break_llc_locality(struct lb_env *env)
 {
-	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB) ||
+	    !static_branch_likely(&sched_cache_present))
 		return 0;
 
 	if (cpus_share_cache(env->src_cpu, env->dst_cpu))
@@ -12914,7 +12926,8 @@ static int active_load_balance_cpu_stop(void *data)
 #ifdef CONFIG_SCHED_CACHE
 		int llc = llc_idx(target_cpu);
 
-		if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB))
+		if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_LB) ||
+		    !static_branch_likely(&sched_cache_present))
 			goto out_unlock;
 
 		if (llc < 0)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4464b92767ad..3e60618a88e9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2857,6 +2857,7 @@ extern unsigned int sysctl_numa_balancing_hot_threshold;
 #ifdef CONFIG_SCHED_CACHE
 extern unsigned int sysctl_llc_aggr_cap;
 extern unsigned int sysctl_llc_aggr_imb;
+extern struct static_key_false sched_cache_present;
 #endif
 
 #ifdef CONFIG_SCHED_HRTICK
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 91a2b7f65fee..8483c02b4d28 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2476,6 +2476,8 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 	int i, ret = -ENOMEM;
 	bool has_asym = false;
 	bool has_cluster = false;
+	bool llc_has_parent_sd = false;
+	unsigned int multi_llcs_node = 1;
 
 #ifdef CONFIG_SCHED_CACHE
 	if (max_llcs < 0) {
@@ -2545,6 +2547,8 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 				struct sched_domain __rcu *top_p;
 				unsigned int nr_llcs;
 
+				if (!llc_has_parent_sd)
+					llc_has_parent_sd = true;
 				/*
 				 * For a single LLC per node, allow an
 				 * imbalance up to 12.5% of the node. This is
@@ -2566,10 +2570,19 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 				 * between LLCs and memory channels.
 				 */
 				nr_llcs = sd->span_weight / child->span_weight;
-				if (nr_llcs == 1)
+				/*
+				 * iff all nodes have multiple LLCs, the
+				 * multi_llcs_node will be set to 1. If
+				 * there is at least 1 node having 1 single
+				 * LLC, the multi_llcs_node remains 0.
+				 */
+				if (nr_llcs == 1) {
 					imb = sd->span_weight >> 3;
-				else
+					multi_llcs_node = 0;
+				} else {
 					imb = nr_llcs;
+					multi_llcs_node &= 1;
+				}
 				imb = max(1U, imb);
 				sd->imb_numa_nr = imb;
 
@@ -2617,6 +2630,11 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 	if (has_cluster)
 		static_branch_inc_cpuslocked(&sched_cluster_active);
 
+#ifdef CONFIG_SCHED_CACHE
+	if (llc_has_parent_sd && multi_llcs_node && !sched_asym_cpucap_active())
+		static_branch_inc_cpuslocked(&sched_cache_present);
+#endif
+
 	if (rq && sched_debug_verbose)
 		pr_info("root domain span: %*pbl\n", cpumask_pr_args(cpu_map));
 
-- 
2.25.1

[RFC PATCH v4 22/28] sched: Turn EPOCH_PERIOD and EPOCH_OLD into tunnable debugfs

[Chen Yu]

Convert EPOCH_PERIOD and EPOCH_OLD into tunable debugfs
entries. Users can adjust the decay rate as needed.
By default, occupancy decays by half every 10 ms.

Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 kernel/sched/debug.c | 2 ++
 kernel/sched/fair.c  | 9 ++++++---
 kernel/sched/sched.h | 2 ++
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 682fd91a42a0..7a9ec03704b9 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -535,6 +535,8 @@ static __init int sched_init_debug(void)
 #ifdef CONFIG_SCHED_CACHE
 	debugfs_create_u32("llc_aggr_cap", 0644, debugfs_sched, &sysctl_llc_aggr_cap);
 	debugfs_create_u32("llc_aggr_imb", 0644, debugfs_sched, &sysctl_llc_aggr_imb);
+	debugfs_create_u32("llc_period", 0644, debugfs_sched, &sysctl_llc_period);
+	debugfs_create_u32("llc_old", 0644, debugfs_sched, &sysctl_llc_old);
 #endif
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 194ec594561b..64f757ad39fc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1175,6 +1175,9 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 #define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
 #define EPOCH_OLD	5		/* 50 ms */
 
+__read_mostly unsigned int sysctl_llc_period    = EPOCH_PERIOD;
+__read_mostly unsigned int sysctl_llc_old       = EPOCH_OLD;
+
 DEFINE_STATIC_KEY_FALSE(sched_cache_present);
 
 static int llc_id(int cpu)
@@ -1283,9 +1286,9 @@ static inline void __update_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
 	long delta = now - rq->cpu_epoch_next;
 
 	if (delta > 0) {
-		n = (delta + EPOCH_PERIOD - 1) / EPOCH_PERIOD;
+		n = (delta + sysctl_llc_period - 1) / sysctl_llc_period;
 		rq->cpu_epoch += n;
-		rq->cpu_epoch_next += n * EPOCH_PERIOD;
+		rq->cpu_epoch_next += n * sysctl_llc_period;
 		__shr_u64(&rq->cpu_runtime, n);
 	}
 
@@ -1346,7 +1349,7 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	 * has only 1 thread, invalidate
 	 * it's preferred state.
 	 */
-	if (epoch - READ_ONCE(mm->mm_sched_epoch) > EPOCH_OLD ||
+	if (epoch - READ_ONCE(mm->mm_sched_epoch) > sysctl_llc_old ||
 	    get_nr_threads(p) <= 1) {
 		mm->mm_sched_cpu = -1;
 		pcpu_sched->occ = 0;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3e60618a88e9..d752d64d4acd 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2858,6 +2858,8 @@ extern unsigned int sysctl_numa_balancing_hot_threshold;
 extern unsigned int sysctl_llc_aggr_cap;
 extern unsigned int sysctl_llc_aggr_imb;
 extern struct static_key_false sched_cache_present;
+extern unsigned int sysctl_llc_period;
+extern unsigned int sysctl_llc_old;
 #endif
 
 #ifdef CONFIG_SCHED_HRTICK
-- 
2.25.1

[RFC PATCH v4 23/28] sched: Scan a task's preferred node for preferred LLC

[Chen Yu]

When sched_cache is enabled, fully scanning all online
CPUs to find the hottest one is very costly. As a first
step, limit the scan to only the CPUs within the task's
preferred node. If the node containing the task's preferred
LLC is not in the CPU scan mask, add it. Additionally, if
the node where the current task is running is not in the
scan mask, add it too.

Suggested-by: Jianyong Wu <jianyong.wu@outlook.com>
Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 kernel/sched/fair.c | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 64f757ad39fc..420d3a080990 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1390,13 +1390,36 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p)
 	}
 }
 
+static void get_scan_cpumasks(cpumask_var_t cpus, int cache_cpu,
+			      int pref_nid, int curr_cpu)
+{
+#ifdef CONFIG_NUMA_BALANCING
+	/* first honor the task's preferred node */
+	if (pref_nid != NUMA_NO_NODE)
+		cpumask_or(cpus, cpus, cpumask_of_node(pref_nid));
+#endif
+
+	/* secondly honor the task's cache CPU if it is not included */
+	if (cache_cpu != -1 && !cpumask_test_cpu(cache_cpu, cpus))
+		cpumask_or(cpus, cpus,
+			   cpumask_of_node(cpu_to_node(cache_cpu)));
+
+	/*
+	 * Thirdly honor the task's current running node
+	 * as the last resort.
+	 */
+	if (!cpumask_test_cpu(curr_cpu, cpus))
+		cpumask_or(cpus, cpus, cpumask_of_node(cpu_to_node(curr_cpu)));
+}
+
 static void __no_profile task_cache_work(struct callback_head *work)
 {
 	struct task_struct *p = current;
 	struct mm_struct *mm = p->mm;
 	unsigned long m_a_occ = 0;
 	unsigned long last_m_a_occ = 0;
-	int cpu, m_a_cpu = -1;
+	int cpu, m_a_cpu = -1, cache_cpu,
+	    pref_nid = NUMA_NO_NODE, curr_cpu = smp_processor_id();
 	cpumask_var_t cpus;
 
 	WARN_ON_ONCE(work != &p->cache_work);
@@ -1406,11 +1429,18 @@ static void __no_profile task_cache_work(struct callback_head *work)
 	if (p->flags & PF_EXITING)
 		return;
 
-	if (!alloc_cpumask_var(&cpus, GFP_KERNEL))
+	if (!zalloc_cpumask_var(&cpus, GFP_KERNEL))
 		return;
 
+	cache_cpu = mm->mm_sched_cpu;
+#ifdef CONFIG_NUMA_BALANCING
+	if (static_branch_likely(&sched_numa_balancing))
+		pref_nid = p->numa_preferred_nid;
+#endif
+
 	scoped_guard (cpus_read_lock) {
-		cpumask_copy(cpus, cpu_online_mask);
+		get_scan_cpumasks(cpus, cache_cpu,
+				  pref_nid, curr_cpu);
 
 		for_each_cpu(cpu, cpus) {
 			/* XXX sched_cluster_active */
-- 
2.25.1

[RFC PATCH v4 24/28] sched: Record average number of runninhg tasks per process

[Chen Yu]

Performance regression was found when running hackbench
with many threads per process(the fd number is high).
To avoid this regression, process having a large number
of active threads should be excluded from cache aware
scheduling.

With sched_cache enabled, record the number of active threads within
the process. This calculation occurs in the periodic task_cache_work():
when iterating over the CPUs, check the currently running task on that
CPU; if the running task belongs to the same process as the task that
launches task_cache_work(), increment the active thread count by 1.

If the number exceeds the number of CPUs in the preferred LLC,
sched_cache is prevented from aggregating too many threads in one
LLC domain.

Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 include/linux/mm_types.h |  1 +
 kernel/sched/fair.c      | 14 ++++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 41a598a44361..13b715357ccb 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1033,6 +1033,7 @@ struct mm_struct {
 		raw_spinlock_t mm_sched_lock;
 		unsigned long mm_sched_epoch;
 		int mm_sched_cpu;
+		u64 nr_running_avg;
 #endif
 
 #ifdef CONFIG_MMU
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 420d3a080990..2577b4225c3f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1414,12 +1414,13 @@ static void get_scan_cpumasks(cpumask_var_t cpus, int cache_cpu,
 
 static void __no_profile task_cache_work(struct callback_head *work)
 {
-	struct task_struct *p = current;
+	struct task_struct *p = current, *cur;
 	struct mm_struct *mm = p->mm;
 	unsigned long m_a_occ = 0;
 	unsigned long last_m_a_occ = 0;
 	int cpu, m_a_cpu = -1, cache_cpu,
-	    pref_nid = NUMA_NO_NODE, curr_cpu = smp_processor_id();
+	    pref_nid = NUMA_NO_NODE, curr_cpu = smp_processor_id(),
+	    nr_running = 0;
 	cpumask_var_t cpus;
 
 	WARN_ON_ONCE(work != &p->cache_work);
@@ -1460,6 +1461,14 @@ static void __no_profile task_cache_work(struct callback_head *work)
 					m_cpu = i;
 				}
 				nr++;
+
+				rcu_read_lock();
+				cur = rcu_dereference(cpu_rq(i)->curr);
+				if (cur && !(cur->flags & (PF_EXITING | PF_KTHREAD)) &&
+				    cur->mm == mm)
+					nr_running++;
+				rcu_read_unlock();
+
 				trace_printk("(%d) occ: %ld m_occ: %ld m_cpu: %d nr: %d\n",
 					     per_cpu(sd_llc_id, i), occ, m_occ, m_cpu, nr);
 			}
@@ -1489,6 +1498,7 @@ static void __no_profile task_cache_work(struct callback_head *work)
 		mm->mm_sched_cpu = m_a_cpu;
 	}
 
+	update_avg(&mm->nr_running_avg, nr_running);
 	free_cpumask_var(cpus);
 }
 
-- 
2.25.1

[RFC PATCH v4 25/28] sched: Skip cache aware scheduling if the process has many active threads

[Chen Yu]

If the number of active threads within the process
exceeds the number of Cores(divided by SMTs number)
in the LLC, do not enable cache-aware scheduling.
This is because there is a risk of cache contention
within the preferred LLC when too many threads are
present.

Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 kernel/sched/fair.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2577b4225c3f..4bf794f170cf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1205,6 +1205,18 @@ static inline int pref_llc_idx(struct task_struct *p)
 	return llc_idx(p->preferred_llc);
 }
 
+static bool exceed_llc_nr(struct mm_struct *mm, int cpu)
+{
+	int smt_nr = 1;
+
+#ifdef CONFIG_SCHED_SMT
+	if (sched_smt_active())
+		smt_nr = cpumask_weight(cpu_smt_mask(cpu));
+#endif
+
+	return ((mm->nr_running_avg * smt_nr) > per_cpu(sd_llc_size, cpu));
+}
+
 static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
 {
 	int pref_llc;
@@ -1350,7 +1362,8 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	 * it's preferred state.
 	 */
 	if (epoch - READ_ONCE(mm->mm_sched_epoch) > sysctl_llc_old ||
-	    get_nr_threads(p) <= 1) {
+	    get_nr_threads(p) <= 1 ||
+	    exceed_llc_nr(mm, cpu_of(rq))) {
 		mm->mm_sched_cpu = -1;
 		pcpu_sched->occ = 0;
 	}
@@ -1430,6 +1443,11 @@ static void __no_profile task_cache_work(struct callback_head *work)
 	if (p->flags & PF_EXITING)
 		return;
 
+	if (get_nr_threads(p) <= 1) {
+		mm->mm_sched_cpu = -1;
+		return;
+	}
+
 	if (!zalloc_cpumask_var(&cpus, GFP_KERNEL))
 		return;
 
@@ -9095,6 +9113,10 @@ static __maybe_unused enum llc_mig_hint get_migrate_hint(int src_cpu, int dst_cp
 	if (cpu < 0)
 		return mig_allow;
 
+	 /* skip cache aware load balance for single/too many threads */
+	if (get_nr_threads(p) <= 1 || exceed_llc_nr(mm, dst_cpu))
+		return mig_allow;
+
 	if (cpus_share_cache(dst_cpu, cpu))
 		return _get_migrate_hint(src_cpu, dst_cpu,
 					 task_util(p), true);
-- 
2.25.1

[RFC PATCH v4 26/28] sched: Do not enable cache aware scheduling for process with large RSS

[Chen Yu]

It has been reported that when running memory-intensive workloads
such as stream, sched_cache may saturate the memory bandwidth on
the preferred LLC.

To prevent this from happening, evaluate the process's memory
footprint by checking the size of RSS (anonymous pages and shared
pages) and comparing it to the size of the LLC. If the former is
larger, skip cache-aware scheduling. This is because if tasks
do not actually share data, aggregating tasks with large RSS will
likely result in cache contention and performance depredation.

However, in theory, RSS is not the same as memory footprint.
This is just an estimated approach to prevent over-aggregation.
The default behavior is to strictly compare the size of RSS with
the size of the LLC. The next patch will introduce a user-provided
hint to customize this comparison.

Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/fair.c | 47 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4bf794f170cf..cbda7dad1305 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1205,6 +1205,34 @@ static inline int pref_llc_idx(struct task_struct *p)
 	return llc_idx(p->preferred_llc);
 }
 
+static bool exceed_llc_capacity(struct mm_struct *mm, int cpu)
+{
+	struct cpu_cacheinfo *this_cpu_ci;
+	struct cacheinfo *l3_leaf;
+	unsigned long rss;
+	unsigned int llc;
+
+	/*
+	 * get_cpu_cacheinfo_level() can not be used
+	 * because it requires the cpu_hotplug_lock
+	 * to be held. Use get_cpu_cacheinfo()
+	 * directly because the 'cpu' can not be
+	 * offlined at the moment.
+	 */
+	this_cpu_ci = get_cpu_cacheinfo(cpu);
+	if (!this_cpu_ci->info_list ||
+	    this_cpu_ci->num_leaves < 3)
+		return true;
+
+	l3_leaf = this_cpu_ci->info_list + 3;
+	llc = l3_leaf->size;
+
+	rss = get_mm_counter(mm, MM_ANONPAGES) +
+		get_mm_counter(mm, MM_SHMEMPAGES);
+
+	return (llc <= (rss * PAGE_SIZE));
+}
+
 static bool exceed_llc_nr(struct mm_struct *mm, int cpu)
 {
 	int smt_nr = 1;
@@ -1363,7 +1391,8 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	 */
 	if (epoch - READ_ONCE(mm->mm_sched_epoch) > sysctl_llc_old ||
 	    get_nr_threads(p) <= 1 ||
-	    exceed_llc_nr(mm, cpu_of(rq))) {
+	    exceed_llc_nr(mm, cpu_of(rq)) ||
+	    exceed_llc_capacity(mm, cpu_of(rq))) {
 		mm->mm_sched_cpu = -1;
 		pcpu_sched->occ = 0;
 	}
@@ -1448,6 +1477,14 @@ static void __no_profile task_cache_work(struct callback_head *work)
 		return;
 	}
 
+	/*
+	 * Do not check exceed_llc_nr() because
+	 * the active number of threads needs to
+	 * been updated anyway.
+	 */
+	if (exceed_llc_capacity(mm, curr_cpu))
+		return;
+
 	if (!zalloc_cpumask_var(&cpus, GFP_KERNEL))
 		return;
 
@@ -9113,8 +9150,12 @@ static __maybe_unused enum llc_mig_hint get_migrate_hint(int src_cpu, int dst_cp
 	if (cpu < 0)
 		return mig_allow;
 
-	 /* skip cache aware load balance for single/too many threads */
-	if (get_nr_threads(p) <= 1 || exceed_llc_nr(mm, dst_cpu))
+	/*
+	 * skip cache aware load balance for single/too many threads
+	 * and large footprint.
+	 */
+	if (get_nr_threads(p) <= 1 || exceed_llc_nr(mm, dst_cpu) ||
+	    exceed_llc_capacity(mm, dst_cpu))
 		return mig_allow;
 
 	if (cpus_share_cache(dst_cpu, cpu))
-- 
2.25.1

[RFC PATCH v4 27/28] sched: Allow the user space to tune the scale factor for RSS comparison

[Chen Yu]

sched_cache compares the process's resident pages with
the size of the LLC to determine whether task aggregation
on the preferred LLC might cause cache contention. If the
former is larger than the latter, skip cache-aware task
aggregation. However, some workloads with large resident
pages have a small memory footprint; such workloads could
benefit from cache-aware scheduling. The kernel lacks a
efficient mechanism to track the task's memory footprint
(yes, we have resctrl, but it is for user-space query,
and not process scope), so it is up to userspace to pass
this hint to the kernel.

Introduce /sys/kernel/debug/sched/sched_cache_ignore_rss
to control the extent to which users ignore the RSS
restriction. This value ranges from 0 to 100. A value of
0 means that the user disables the cache aware scheduling.
1 means if a process's RSS is larger than the LLC size,
cache-aware scheduling will be skipped. 100 means cache
aware scheduling is alwasy enabled regardless of RSS size.
N (between 1 and 100) means turn off cache aware scheduling
when RSS is greater than (N-1) * 256 * LLC size

For example, suppose the L3 size is 32MB. If the
sysctl_sched_cache_ignore_rss is 1: When the RSS is larger
than 32MB, the process is regarded as exceeding the LLC capacity.
If the sysctl_sched_cache_ignore_rss is 99: When the RSS is
larger than 784GB, the process is regarded as exceeding the
LLC capacity(please refer to the code):
784GB = (1 + (99 - 1) * 256) * 32MB

Additionally, the number of SMTs is also considered for
sysctl_sched_cache_aggr_cap; if there are many SMTs in the core,
sysctl_llc_aggr_cap will be reduced. This inhibits task aggregation
from cache-aware scheduling on systems with a high number of SMTs,
like Power 10 and Power 11.

Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reported-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Reported-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
 kernel/sched/debug.c | 82 +++++++++++++++++++++++++++++++++++++++++++-
 kernel/sched/fair.c  | 10 ++++--
 kernel/sched/sched.h |  3 +-
 3 files changed, 90 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 7a9ec03704b9..6676fc2a8c08 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -166,6 +166,83 @@ static const struct file_operations sched_feat_fops = {
 	.release	= single_release,
 };
 
+#ifdef CONFIG_SCHED_CACHE
+#define SCHED_CACHE_CREATE_CONTROL(name, val)			  \
+static int sysctl_sched_cache_##name = val;			  \
+static ssize_t sched_cache_write_##name(struct file *filp,	  \
+					const char __user *ubuf,  \
+					size_t cnt, loff_t *ppos) \
+{								  \
+	char buf[16];						  \
+	unsigned int percent;					  \
+	if (cnt > 15)						  \
+		cnt = 15;					  \
+	if (copy_from_user(&buf, ubuf, cnt))			  \
+		return -EFAULT;					  \
+	buf[cnt] = '\0';					  \
+	if (kstrtouint(buf, 10, &percent))			  \
+		return -EINVAL;					  \
+	if (percent > 100)					  \
+		return -EINVAL;					  \
+	sysctl_sched_cache_##name = percent;			  \
+	*ppos += cnt;						  \
+	return cnt;						  \
+}								  \
+static int sched_cache_show_##name(struct seq_file *m, void *v)	  \
+{								  \
+	seq_printf(m, "%d\n", sysctl_sched_cache_##name);	  \
+	return 0;						  \
+}								  \
+static int sched_cache_open_##name(struct inode *inode,		  \
+				   struct file *filp)		  \
+{								  \
+	return single_open(filp, sched_cache_show_##name, NULL);  \
+}								  \
+static const struct file_operations sched_cache_fops_##name = {	  \
+	.open		= sched_cache_open_##name,		  \
+	.write		= sched_cache_write_##name,		  \
+	.read		= seq_read,				  \
+	.llseek		= seq_lseek,				  \
+	.release	= single_release,			  \
+}
+
+SCHED_CACHE_CREATE_CONTROL(ignore_rss, 1);
+int get_sched_cache_rss_scale(void)
+{
+	if (!sysctl_sched_cache_ignore_rss)
+		return 0;
+
+	if (sysctl_sched_cache_ignore_rss >= 100)
+		return INT_MAX;
+	/*
+	 * Suppose the L3 size is 32MB. If the
+	 * sysctl_sched_cache_ignore_rss is 1:
+	 * When the RSS is larger than 32MB,
+	 * the process is regarded as exceeding
+	 * the LLC capacity. If the
+	 * sysctl_sched_cache_ignore_rss is 99:
+	 * When the RSS is larger than 784GB,
+	 * the process is regarded as exceeding
+	 * the LLC capacity:
+	 * 784GB = (1 + (99 - 1) * 256) * 32MB
+	 */
+	return (1 + (sysctl_sched_cache_ignore_rss - 1) * 256);
+}
+
+SCHED_CACHE_CREATE_CONTROL(aggr_cap, 50);
+int get_sched_cache_cap_scale(void)
+{
+	int smt_nr = 1;
+
+#ifdef CONFIG_SCHED_SMT
+	if (sched_smt_active())
+		smt_nr =
+			cpumask_weight(cpu_smt_mask(raw_smp_processor_id()));
+#endif
+	return (sysctl_sched_cache_aggr_cap / smt_nr);
+}
+#endif /* SCHED_CACHE */
+
 #ifdef CONFIG_SMP
 
 static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
@@ -533,10 +610,13 @@ static __init int sched_init_debug(void)
 #endif
 
 #ifdef CONFIG_SCHED_CACHE
-	debugfs_create_u32("llc_aggr_cap", 0644, debugfs_sched, &sysctl_llc_aggr_cap);
 	debugfs_create_u32("llc_aggr_imb", 0644, debugfs_sched, &sysctl_llc_aggr_imb);
 	debugfs_create_u32("llc_period", 0644, debugfs_sched, &sysctl_llc_period);
 	debugfs_create_u32("llc_old", 0644, debugfs_sched, &sysctl_llc_old);
+	debugfs_create_file("llc_aggr_cap", 0644, debugfs_sched, NULL,
+			    &sched_cache_fops_aggr_cap);
+	debugfs_create_file("llc_ignore_rss", 0644, debugfs_sched, NULL,
+			    &sched_cache_fops_ignore_rss);
 #endif
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cbda7dad1305..018825f04063 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1211,6 +1211,7 @@ static bool exceed_llc_capacity(struct mm_struct *mm, int cpu)
 	struct cacheinfo *l3_leaf;
 	unsigned long rss;
 	unsigned int llc;
+	int scale;
 
 	/*
 	 * get_cpu_cacheinfo_level() can not be used
@@ -1230,7 +1231,11 @@ static bool exceed_llc_capacity(struct mm_struct *mm, int cpu)
 	rss = get_mm_counter(mm, MM_ANONPAGES) +
 		get_mm_counter(mm, MM_SHMEMPAGES);
 
-	return (llc <= (rss * PAGE_SIZE));
+	scale = get_sched_cache_rss_scale();
+	if (scale == INT_MAX)
+		return false;
+
+	return ((llc * scale) <= (rss * PAGE_SIZE));
 }
 
 static bool exceed_llc_nr(struct mm_struct *mm, int cpu)
@@ -9037,7 +9042,6 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 static long __migrate_degrades_locality(struct task_struct *p,
 					int src_cpu, int dst_cpu,
 					bool idle);
-__read_mostly unsigned int sysctl_llc_aggr_cap       = 50;
 __read_mostly unsigned int sysctl_llc_aggr_imb       = 20;
 
 /*
@@ -9049,7 +9053,7 @@ __read_mostly unsigned int sysctl_llc_aggr_imb       = 20;
  * (default: ~50%)
  */
 #define fits_llc_capacity(util, max)	\
-	((util) * 100 < (max) * sysctl_llc_aggr_cap)
+	((util) * 100 < (max) * get_sched_cache_cap_scale())
 
 /*
  * The margin used when comparing utilization.
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d752d64d4acd..eaeca4e77ead 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2855,11 +2855,12 @@ extern unsigned int sysctl_numa_balancing_scan_size;
 extern unsigned int sysctl_numa_balancing_hot_threshold;
 
 #ifdef CONFIG_SCHED_CACHE
-extern unsigned int sysctl_llc_aggr_cap;
 extern unsigned int sysctl_llc_aggr_imb;
 extern struct static_key_false sched_cache_present;
 extern unsigned int sysctl_llc_period;
 extern unsigned int sysctl_llc_old;
+int get_sched_cache_rss_scale(void);
+int get_sched_cache_cap_scale(void);
 #endif
 
 #ifdef CONFIG_SCHED_HRTICK
-- 
2.25.1

[RFC PATCH v4 28/28] sched: Add ftrace to track cache aware load balance and hottest CPU changes

[Chen Yu]

Introduce 3 trace events:

1.
The average time spent scanning CPUs and calculating occupancy
in each sample period. This event can be used to track the
overhead of cache-aware scheduling.

2.
The footprint when switching to a new mm_sched_cpu (a cache-hot CPU).
This event can be used to track whether there is any abnormal
bouncing of mm_sched_cpu.

3.
The footprint of load balancing when migrating a task between CPUs.
This event can be used to track whether cache-aware load balancing
behaves as expected.

All these events can be used with bpftrace to gain a basic
understanding of whether cache-aware scheduling is effective.

Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 include/trace/events/sched.h | 93 ++++++++++++++++++++++++++++++++++++
 kernel/sched/fair.c          | 25 ++++++++--
 2 files changed, 113 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 4e6b2910cec3..398180c18946 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -10,6 +10,99 @@
 #include <linux/tracepoint.h>
 #include <linux/binfmts.h>
 
+TRACE_EVENT(sched_scan_cost,
+
+	TP_PROTO(struct task_struct *t, u64 cost, int nr,
+		 u64 old_running, u64 new_running),
+
+	TP_ARGS(t, cost, nr, old_running, new_running),
+
+	TP_STRUCT__entry(
+		__array(	char,	comm,	TASK_COMM_LEN	)
+		__field(	pid_t,	pid			)
+		__field(	u64,	cost			)
+		__field(	int,	nr			)
+		__field(	u64,	old_running		)
+		__field(	u64,	new_running		)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+		__entry->pid	= t->pid;
+		__entry->cost	= cost;
+		__entry->nr	= nr;
+		__entry->old_running	= old_running;
+		__entry->new_running	= new_running;
+	),
+
+	TP_printk("comm=%s pid=%d cost=%llu nr=%d old_r=%lld new_r=%lld",
+		  __entry->comm, __entry->pid,
+		  __entry->cost, __entry->nr,
+		  __entry->old_running, __entry->new_running)
+);
+
+TRACE_EVENT(sched_cache_work,
+
+	TP_PROTO(struct task_struct *t, int pref_cpu, int pref_llc,
+		 int new_cpu, int new_llc),
+
+	TP_ARGS(t, pref_cpu, pref_llc, new_cpu, new_llc),
+
+	TP_STRUCT__entry(
+		__array(	char,	comm,	TASK_COMM_LEN	)
+		__field(	pid_t,	pid			)
+		__field(	int,	pref_cpu		)
+		__field(	int,	pref_llc		)
+		__field(	int,	new_cpu			)
+		__field(	int,	new_llc			)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+		__entry->pid	= t->pid;
+		__entry->pref_cpu	= pref_cpu;
+		__entry->pref_llc	= pref_llc;
+		__entry->new_cpu	= new_cpu;
+		__entry->new_llc	= new_llc;
+	),
+
+	TP_printk("comm=%s pid=%d pref_cpu=%d pref_llc=%d attach_cpu=%d attach_llc=%d",
+		  __entry->comm, __entry->pid,
+		  __entry->pref_cpu, __entry->pref_llc,
+		  __entry->new_cpu, __entry->new_llc)
+);
+
+TRACE_EVENT(sched_attach_task,
+
+	TP_PROTO(struct task_struct *t, int pref_cpu, int pref_llc,
+		 int attach_cpu, int attach_llc),
+
+	TP_ARGS(t, pref_cpu, pref_llc, attach_cpu, attach_llc),
+
+	TP_STRUCT__entry(
+		__array(	char,	comm,	TASK_COMM_LEN	)
+		__field(	pid_t,	pid			)
+		__field(	int,	pref_cpu		)
+		__field(	int,	pref_llc		)
+		__field(	int,	attach_cpu		)
+		__field(	int,	attach_llc		)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+		__entry->pid	= t->pid;
+		__entry->pref_cpu	= pref_cpu;
+		__entry->pref_llc	= pref_llc;
+		__entry->attach_cpu	= attach_cpu;
+		__entry->attach_llc	= attach_llc;
+	),
+
+	TP_printk("comm=%s pid=%d pref_cpu=%d pref_llc=%d attach_cpu=%d attach_llc=%d",
+		  __entry->comm, __entry->pid,
+		  __entry->pref_cpu, __entry->pref_llc,
+		  __entry->attach_cpu, __entry->attach_llc)
+);
+
 /*
  * Tracepoint for calling kthread_stop, performed to end a kthread:
  */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 018825f04063..cb2c33ee0d92 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1467,8 +1467,9 @@ static void __no_profile task_cache_work(struct callback_head *work)
 	unsigned long last_m_a_occ = 0;
 	int cpu, m_a_cpu = -1, cache_cpu,
 	    pref_nid = NUMA_NO_NODE, curr_cpu = smp_processor_id(),
-	    nr_running = 0;
+	    nr_running = 0, nr_scan = 0;
 	cpumask_var_t cpus;
+	u64 t0, scan_cost = 0;
 
 	WARN_ON_ONCE(work != &p->cache_work);
 
@@ -1499,6 +1500,7 @@ static void __no_profile task_cache_work(struct callback_head *work)
 		pref_nid = p->numa_preferred_nid;
 #endif
 
+	t0 = sched_clock_cpu(curr_cpu);
 	scoped_guard (cpus_read_lock) {
 		get_scan_cpumasks(cpus, cache_cpu,
 				  pref_nid, curr_cpu);
@@ -1521,6 +1523,7 @@ static void __no_profile task_cache_work(struct callback_head *work)
 					m_cpu = i;
 				}
 				nr++;
+				nr_scan++;
 
 				rcu_read_lock();
 				cur = rcu_dereference(cpu_rq(i)->curr);
@@ -1529,8 +1532,8 @@ static void __no_profile task_cache_work(struct callback_head *work)
 					nr_running++;
 				rcu_read_unlock();
 
-				trace_printk("(%d) occ: %ld m_occ: %ld m_cpu: %d nr: %d\n",
-					     per_cpu(sd_llc_id, i), occ, m_occ, m_cpu, nr);
+				//trace_printk("(%d) occ: %ld m_occ: %ld m_cpu: %d nr: %d\n",
+				//	     per_cpu(sd_llc_id, i), occ, m_occ, m_cpu, nr);
 			}
 
 			// a_occ /= nr;
@@ -1541,8 +1544,8 @@ static void __no_profile task_cache_work(struct callback_head *work)
 			if (llc_id(cpu) == llc_id(mm->mm_sched_cpu))
 				last_m_a_occ = a_occ;
 
-			trace_printk("(%d) a_occ: %ld m_a_occ: %ld\n",
-				     per_cpu(sd_llc_id, cpu), a_occ, m_a_occ);
+			//trace_printk("(%d) a_occ: %ld m_a_occ: %ld\n",
+			//	     per_cpu(sd_llc_id, cpu), a_occ, m_a_occ);
 
 			for_each_cpu(i, sched_domain_span(sd)) {
 				/* XXX threshold ? */
@@ -1553,12 +1556,17 @@ static void __no_profile task_cache_work(struct callback_head *work)
 		}
 	}
 
+	scan_cost = sched_clock_cpu(curr_cpu) - t0;
+
 	if (m_a_occ > (2 * last_m_a_occ)) {
 		/* avoid the bouncing of mm_sched_cpu */
+		trace_sched_cache_work(p, mm->mm_sched_cpu, llc_id(mm->mm_sched_cpu),
+					m_a_cpu, llc_id(m_a_cpu));
 		mm->mm_sched_cpu = m_a_cpu;
 	}
 
 	update_avg(&mm->nr_running_avg, nr_running);
+	trace_sched_scan_cost(p, scan_cost, nr_scan, mm->nr_running_avg, nr_running);
 	free_cpumask_var(cpus);
 }
 
@@ -10443,6 +10451,13 @@ static void attach_task(struct rq *rq, struct task_struct *p)
 {
 	lockdep_assert_rq_held(rq);
 
+#ifdef CONFIG_SCHED_CACHE
+	if (p->mm)
+		trace_sched_attach_task(p,
+					p->mm->mm_sched_cpu,
+					p->mm->mm_sched_cpu != -1 ? llc_id(p->mm->mm_sched_cpu) : -1,
+					cpu_of(rq), llc_id(cpu_of(rq)));
+#endif
 	WARN_ON_ONCE(task_rq(p) != rq);
 	activate_task(rq, p, ENQUEUE_NOCLOCK);
 	wakeup_preempt(rq, p, 0);
-- 
2.25.1

Re: [RFC PATCH v4 01/28] sched: Cache aware load-balancing

[kernel test robot]

Hello,

kernel test robot noticed "Oops:general_protection_fault,probably_for_non-canonical_address#:#[##]SMP_KASAN" on:

commit: 2ae6ef14daceb295598846a328dd65fde6b16c99 ("[RFC PATCH v4 01/28] sched: Cache aware load-balancing")
url: https://github.com/intel-lab-lkp/linux/commits/Chen-Yu/sched-Cache-aware-load-balancing/20250809-131716
base: v6.16
patch link: https://lore.kernel.org/all/9157186cf9e3fd541f62c637579ff736b3704c51.1754712565.git.tim.c.chen@linux.intel.com/
patch subject: [RFC PATCH v4 01/28] sched: Cache aware load-balancing

in testcase: boot

config: x86_64-randconfig-103-20250810
compiler: gcc-12
test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G

(please refer to attached dmesg/kmsg for entire log/backtrace)


+----------------------------------------------------------------------------------+-------+------------+
|                                                                                  | v6.16 | 2ae6ef14da |
+----------------------------------------------------------------------------------+-------+------------+
| Oops:general_protection_fault,probably_for_non-canonical_address#:#[##]SMP_KASAN | 0     | 5          |
| KASAN:null-ptr-deref_in_range[#-#]                                               | 0     | 5          |
| RIP:_find_next_bit                                                               | 0     | 5          |
| Kernel_panic-not_syncing:Fatal_exception                                         | 0     | 5          |
+----------------------------------------------------------------------------------+-------+------------+


If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202508111054.58c525c-lkp@intel.com


[   18.108061][    T1] usbcore: registered new interface driver i2c-diolan-u2c
[   18.111512][   T36] input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input0
[   18.113593][    T1] Driver for 1-wire Dallas network protocol.
[   18.119966][    T1] f71882fg: Not a Fintek device
[   18.120517][    T1] f71882fg: Not a Fintek device
[   18.142462][   T63] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] SMP KASAN
[   18.144289][   T63] KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
[   18.145594][   T63] CPU: 0 UID: 0 PID: 63 Comm: modprobe Not tainted 6.16.0-00001-g2ae6ef14dace #1 PREEMPT(none)
[   18.146207][   T63] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[ 18.146207][ T63] RIP: 0010:_find_next_bit (kbuild/src/consumer/lib/find_bit.c:156 (discriminator 2)) 
[ 18.146207][ T63] Code: 48 89 d3 48 83 c8 ff 83 e2 3f 49 89 fe 48 c1 eb 06 c4 62 e9 f7 e8 b8 ff ff 37 00 4c 8d 3c df 48 c1 e0 2a 4c 89 fa 48 c1 ea 03 <80> 3c 02 00 74 08 4c 89 ff e8 cc 76 52 ff 49 8b 07 4c 21 e8 49 bd
All code
========
   0:	48 89 d3             	mov    %rdx,%rbx
   3:	48 83 c8 ff          	or     $0xffffffffffffffff,%rax
   7:	83 e2 3f             	and    $0x3f,%edx
   a:	49 89 fe             	mov    %rdi,%r14
   d:	48 c1 eb 06          	shr    $0x6,%rbx
  11:	c4 62 e9 f7 e8       	shlx   %rdx,%rax,%r13
  16:	b8 ff ff 37 00       	mov    $0x37ffff,%eax
  1b:	4c 8d 3c df          	lea    (%rdi,%rbx,8),%r15
  1f:	48 c1 e0 2a          	shl    $0x2a,%rax
  23:	4c 89 fa             	mov    %r15,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
  2a:*	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)		<-- trapping instruction
  2e:	74 08                	je     0x38
  30:	4c 89 ff             	mov    %r15,%rdi
  33:	e8 cc 76 52 ff       	call   0xffffffffff527704
  38:	49 8b 07             	mov    (%r15),%rax
  3b:	4c 21 e8             	and    %r13,%rax
  3e:	49                   	rex.WB
  3f:	bd                   	.byte 0xbd

Code starting with the faulting instruction
===========================================
   0:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
   4:	74 08                	je     0xe
   6:	4c 89 ff             	mov    %r15,%rdi
   9:	e8 cc 76 52 ff       	call   0xffffffffff5276da
   e:	49 8b 07             	mov    (%r15),%rax
  11:	4c 21 e8             	and    %r13,%rax
  14:	49                   	rex.WB
  15:	bd                   	.byte 0xbd
[   18.146207][   T63] RSP: 0000:ffffc900001f7d28 EFLAGS: 00010206
[   18.146207][   T63] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: fffffbfff0bdd81a
[   18.146207][   T63] RDX: 0000000000000012 RSI: 0000000000000002 RDI: 0000000000000090
[   18.146207][   T63] RBP: ffffc900001f7d50 R08: 0000000000000000 R09: 0000000000000003
[   18.146207][   T63] R10: ffffffff8145362f R11: ffffed103099ffd5 R12: 0000000000000002
[   18.146207][   T63] R13: ffffffffffffffff R14: 0000000000000090 R15: 0000000000000090
[   18.146207][   T63] FS:  0000000000000000(0000) GS:ffff888428798000(0000) knlGS:0000000000000000
[   18.146207][   T63] CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
[   18.146207][   T63] CR2: 00000000f7fc18c8 CR3: 0000000185368000 CR4: 00000000000406b0
[   18.146207][   T63] Call Trace:
[   18.146207][   T63]  <TASK>
[ 18.146207][ T63] task_cache_work (kbuild/src/consumer/include/linux/find.h:71 (discriminator 2) kbuild/src/consumer/kernel/sched/fair.c:1325 (discriminator 2)) 
[ 18.146207][ T63] ? _raw_spin_unlock_irq (kbuild/src/consumer/arch/x86/include/asm/paravirt.h:671 kbuild/src/consumer/include/linux/spinlock_api_smp.h:159 kbuild/src/consumer/kernel/locking/spinlock.c:202) 
[ 18.146207][ T63] ? __pfx_task_cache_work (kbuild/src/consumer/kernel/sched/fair.c:1299) 
[ 18.146207][ T63] ? __this_cpu_preempt_check (kbuild/src/consumer/lib/smp_processor_id.c:67) 


The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20250811/202508111054.58c525c-lkp@intel.com



-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [RFC PATCH v4 23/28] sched: Scan a task's preferred node for preferred LLC

[kernel test robot]

Hello,

kernel test robot noticed "BUG:using_smp_processor_id()in_preemptible" on:

commit: ff797757d658ecda432e4c33c0cfc2b704af2b06 ("[RFC PATCH v4 23/28] sched: Scan a task's preferred node for preferred LLC")
url: https://github.com/intel-lab-lkp/linux/commits/Chen-Yu/sched-Cache-aware-load-balancing/20250809-131716
base: v6.16
patch link: https://lore.kernel.org/all/178bf43d7cbc9b2c9aea408dd56b87391067df37.1754712565.git.tim.c.chen@linux.intel.com/
patch subject: [RFC PATCH v4 23/28] sched: Scan a task's preferred node for preferred LLC

in testcase: boot

config: x86_64-randconfig-103-20250810
compiler: gcc-12
test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G

(please refer to attached dmesg/kmsg for entire log/backtrace)


+------------------------------------------------------+------------+------------+
|                                                      | 552a2db758 | ff797757d6 |
+------------------------------------------------------+------------+------------+
| BUG:using_smp_processor_id()in_preemptible           | 0          | 11         |
+------------------------------------------------------+------------+------------+


If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202508120315.19f6266a-lkp@intel.com


[   19.177186][   T64] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/64
[ 19.179622][ T64] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.181347][   T64] CPU: 0 UID: 0 PID: 64 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.181372][   T64] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.181385][   T64] Call Trace:
[   19.181391][   T64]  <TASK>
[ 19.181401][ T64] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.181440][ T64] dump_stack (lib/dump_stack.c:130) 
[ 19.181465][ T64] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.181494][ T64] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.181514][ T64] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.181531][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.181569][ T64] ? lock_is_held (include/linux/lockdep.h:249) 
[ 19.181594][ T64] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.181626][ T64] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.181642][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.181663][ T64] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.181697][ T64] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.181724][ T64] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.181747][ T64] ? preempt_latency_start (include/linux/ftrace.h:1091 kernel/sched/core.c:5866) 
[ 19.181782][ T64] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.181817][ T64] irqentry_exit_to_user_mode (kernel/entry/common.c:124 include/linux/entry-common.h:330 kernel/entry/common.c:184) 
[ 19.181843][ T64] irqentry_exit (kernel/entry/common.c:287) 
[ 19.181862][ T64] exc_page_fault (arch/x86/mm/fault.c:1536) 
[ 19.181898][ T64] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623) 
[   19.181916][   T64] RIP: 0023:0xf7ee9067
[ 19.181933][ T64] Code: fe ff ff 8b 00 85 c0 0f 84 96 00 00 00 8b 8d 60 fe ff ff 8b 51 30 85 d2 74 03 01 42 04 8b 8d 60 fe ff ff 8b 51 2c 85 d2 74 03 <01> 42 04 8b bd 60 fe ff ff 8b 57 34 85 d2 74 03 01 42 04 8b 8d 60
All code
========
   0:	fe                   	(bad)
   1:	ff                   	(bad)
   2:	ff 8b 00 85 c0 0f    	decl   0xfc08500(%rbx)
   8:	84 96 00 00 00 8b    	test   %dl,-0x75000000(%rsi)
   e:	8d 60 fe             	lea    -0x2(%rax),%esp
  11:	ff                   	(bad)
  12:	ff 8b 51 30 85 d2    	decl   -0x2d7acfaf(%rbx)
  18:	74 03                	je     0x1d
  1a:	01 42 04             	add    %eax,0x4(%rdx)
  1d:	8b 8d 60 fe ff ff    	mov    -0x1a0(%rbp),%ecx
  23:	8b 51 2c             	mov    0x2c(%rcx),%edx
  26:	85 d2                	test   %edx,%edx
  28:	74 03                	je     0x2d
  2a:*	01 42 04             	add    %eax,0x4(%rdx)		<-- trapping instruction
  2d:	8b bd 60 fe ff ff    	mov    -0x1a0(%rbp),%edi
  33:	8b 57 34             	mov    0x34(%rdi),%edx
  36:	85 d2                	test   %edx,%edx
  38:	74 03                	je     0x3d
  3a:	01 42 04             	add    %eax,0x4(%rdx)
  3d:	8b                   	.byte 0x8b
  3e:	8d                   	.byte 0x8d
  3f:	60                   	(bad)

Code starting with the faulting instruction
===========================================
   0:	01 42 04             	add    %eax,0x4(%rdx)
   3:	8b bd 60 fe ff ff    	mov    -0x1a0(%rbp),%edi
   9:	8b 57 34             	mov    0x34(%rdi),%edx
   c:	85 d2                	test   %edx,%edx
   e:	74 03                	je     0x13
  10:	01 42 04             	add    %eax,0x4(%rdx)
  13:	8b                   	.byte 0x8b
  14:	8d                   	.byte 0x8d
  15:	60                   	(bad)
[   19.181949][   T64] RSP: 002b:00000000fffd59c0 EFLAGS: 00010206
[   19.181966][   T64] RAX: 00000000565ad000 RBX: 0000000000000001 RCX: 00000000f7f11980
[   19.181978][   T64] RDX: 00000000565dbd44 RSI: 00000000effffef5 RDI: 000000006fffffff
[   19.181990][   T64] RBP: 00000000fffd5bb8 R08: 0000000000000000 R09: 0000000000000000
[   19.182001][   T64] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.182013][   T64] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.182063][   T64]  </TASK>
[   19.230078][   T64] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/64
[ 19.230948][ T64] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.231549][   T64] CPU: 0 UID: 0 PID: 64 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.231557][   T64] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.231561][   T64] Call Trace:
[   19.231564][   T64]  <TASK>
[ 19.231567][ T64] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.231580][ T64] dump_stack (lib/dump_stack.c:130) 
[ 19.231588][ T64] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.231598][ T64] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.231604][ T64] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.231615][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.231627][ T64] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.231637][ T64] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.231643][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.231649][ T64] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.231659][ T64] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.231668][ T64] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.231680][ T64] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.231691][ T64] irqentry_exit_to_user_mode (kernel/entry/common.c:124 include/linux/entry-common.h:330 kernel/entry/common.c:184) 
[ 19.231699][ T64] irqentry_exit (kernel/entry/common.c:287) 
[ 19.231705][ T64] exc_page_fault (arch/x86/mm/fault.c:1536) 
[ 19.231717][ T64] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623) 
[   19.231723][   T64] RIP: 0023:0xf7f03797
[ 19.231729][ T64] Code: 24 0c e3 2c 89 d7 83 e2 03 74 11 7a 04 aa 49 74 1f aa 49 74 1b 83 f2 01 75 02 aa 49 89 ca c1 e9 02 83 e2 03 69 c0 01 01 01 01 <f3> ab 89 d1 f3 aa 8b 44 24 08 5f c3 66 90 66 90 66 90 66 90 66 90
All code
========
   0:	24 0c                	and    $0xc,%al
   2:	e3 2c                	jrcxz  0x30
   4:	89 d7                	mov    %edx,%edi
   6:	83 e2 03             	and    $0x3,%edx
   9:	74 11                	je     0x1c
   b:	7a 04                	jp     0x11
   d:	aa                   	stos   %al,%es:(%rdi)
   e:	49 74 1f             	rex.WB je 0x30
  11:	aa                   	stos   %al,%es:(%rdi)
  12:	49 74 1b             	rex.WB je 0x30
  15:	83 f2 01             	xor    $0x1,%edx
  18:	75 02                	jne    0x1c
  1a:	aa                   	stos   %al,%es:(%rdi)
  1b:	49 89 ca             	mov    %rcx,%r10
  1e:	c1 e9 02             	shr    $0x2,%ecx
  21:	83 e2 03             	and    $0x3,%edx
  24:	69 c0 01 01 01 01    	imul   $0x1010101,%eax,%eax
  2a:*	f3 ab                	rep stos %eax,%es:(%rdi)		<-- trapping instruction
  2c:	89 d1                	mov    %edx,%ecx
  2e:	f3 aa                	rep stos %al,%es:(%rdi)
  30:	8b 44 24 08          	mov    0x8(%rsp),%eax
  34:	5f                   	pop    %rdi
  35:	c3                   	ret
  36:	66 90                	xchg   %ax,%ax
  38:	66 90                	xchg   %ax,%ax
  3a:	66 90                	xchg   %ax,%ax
  3c:	66 90                	xchg   %ax,%ax
  3e:	66 90                	xchg   %ax,%ax

Code starting with the faulting instruction
===========================================
   0:	f3 ab                	rep stos %eax,%es:(%rdi)
   2:	89 d1                	mov    %edx,%ecx
   4:	f3 aa                	rep stos %al,%es:(%rdi)
   6:	8b 44 24 08          	mov    0x8(%rsp),%eax
   a:	5f                   	pop    %rdi
   b:	c3                   	ret
   c:	66 90                	xchg   %ax,%ax
   e:	66 90                	xchg   %ax,%ax
  10:	66 90                	xchg   %ax,%ax
  12:	66 90                	xchg   %ax,%ax
  14:	66 90                	xchg   %ax,%ax
[   19.231735][   T64] RSP: 002b:00000000fffd4f58 EFLAGS: 00010206
[   19.231741][   T64] RAX: 0000000000000000 RBX: 00000000f7f11000 RCX: 0000000000000001
[   19.231745][   T64] RDX: 0000000000000000 RSI: 00000000f7edf148 RDI: 00000000f7edf144
[   19.231749][   T64] RBP: 00000000fffd5138 R08: 0000000000000000 R09: 0000000000000000
[   19.231753][   T64] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.231756][   T64] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.231771][   T64]  </TASK>
[   19.251371][   T64] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/64
[ 19.252249][ T64] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.252877][   T64] CPU: 0 UID: 0 PID: 64 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.252886][   T64] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.252890][   T64] Call Trace:
[   19.252892][   T64]  <TASK>
[ 19.252895][ T64] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.252907][ T64] dump_stack (lib/dump_stack.c:130) 
[ 19.252916][ T64] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.252925][ T64] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.252931][ T64] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.252941][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.252953][ T64] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.252963][ T64] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.252969][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.252976][ T64] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.252985][ T64] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.252994][ T64] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.253006][ T64] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.253018][ T64] exit_to_user_mode_loop (kernel/entry/common.c:124) 
[ 19.253025][ T64] do_int80_emulation (include/linux/entry-common.h:332 include/linux/entry-common.h:414 include/linux/entry-common.h:449 arch/x86/entry/syscall_32.c:175) 
[ 19.253035][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.253044][ T64] ? preempt_latency_start (include/linux/ftrace.h:1091 kernel/sched/core.c:5866) 
[ 19.253055][ T64] ? __up_write (arch/x86/include/asm/preempt.h:104 kernel/locking/rwsem.c:1375) 
[ 19.253061][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.253070][ T64] ? validate_chain (kernel/locking/lockdep.c:3826 kernel/locking/lockdep.c:3879) 
[ 19.253081][ T64] ? __lock_acquire (kernel/locking/lockdep.c:5240) 
[ 19.253093][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.253106][ T64] ? validate_chain (kernel/locking/lockdep.c:3826 kernel/locking/lockdep.c:3879) 
[ 19.253117][ T64] ? __lock_acquire (kernel/locking/lockdep.c:5240) 
[ 19.253128][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.253138][ T64] ? vtime_user_exit (kernel/sched/cputime.c:737) 
[ 19.253149][ T64] ? vtime_user_exit (kernel/sched/cputime.c:737) 
[ 19.253159][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.253170][ T64] ? debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.253177][ T64] ? rcu_is_watching (include/linux/context_tracking.h:128 kernel/rcu/tree.c:745) 
[ 19.253185][ T64] ? trace_irq_disable (include/trace/events/preemptirq.h:36 (discriminator 21)) 
[ 19.253195][ T64] ? trace_hardirqs_off_finish (kernel/trace/trace_preemptirq.c:98) 
[ 19.253203][ T64] ? do_int80_emulation (arch/x86/include/asm/jump_label.h:36 arch/x86/entry/syscall_32.c:148) 
[ 19.253212][ T64] asm_int80_emulation (arch/x86/include/asm/idtentry.h:626) 
[   19.253218][   T64] RIP: 0023:0xf7f02cb0
[ 19.253223][ T64] Code: 4c 24 34 89 44 24 0c 8b 44 24 44 8b 54 24 38 8b 74 24 3c 8b 7c 24 40 a9 ff 0f 00 00 75 1c c1 e8 0c 89 c5 b8 c0 00 00 00 cd 80 <3d> 00 f0 ff ff 77 21 83 c4 1c 5b 5e 5f 5d c3 90 83 c4 1c b8 ea ff
All code
========
   0:	4c 24 34             	rex.WR and $0x34,%al
   3:	89 44 24 0c          	mov    %eax,0xc(%rsp)
   7:	8b 44 24 44          	mov    0x44(%rsp),%eax
   b:	8b 54 24 38          	mov    0x38(%rsp),%edx
   f:	8b 74 24 3c          	mov    0x3c(%rsp),%esi
  13:	8b 7c 24 40          	mov    0x40(%rsp),%edi
  17:	a9 ff 0f 00 00       	test   $0xfff,%eax
  1c:	75 1c                	jne    0x3a
  1e:	c1 e8 0c             	shr    $0xc,%eax
  21:	89 c5                	mov    %eax,%ebp
  23:	b8 c0 00 00 00       	mov    $0xc0,%eax
  28:	cd 80                	int    $0x80
  2a:*	3d 00 f0 ff ff       	cmp    $0xfffff000,%eax		<-- trapping instruction
  2f:	77 21                	ja     0x52
  31:	83 c4 1c             	add    $0x1c,%esp
  34:	5b                   	pop    %rbx
  35:	5e                   	pop    %rsi
  36:	5f                   	pop    %rdi
  37:	5d                   	pop    %rbp
  38:	c3                   	ret
  39:	90                   	nop
  3a:	83 c4 1c             	add    $0x1c,%esp
  3d:	b8                   	.byte 0xb8
  3e:	ea                   	(bad)
  3f:	ff                   	.byte 0xff

Code starting with the faulting instruction
===========================================
   0:	3d 00 f0 ff ff       	cmp    $0xfffff000,%eax
   5:	77 21                	ja     0x28
   7:	83 c4 1c             	add    $0x1c,%esp
   a:	5b                   	pop    %rbx
   b:	5e                   	pop    %rsi
   c:	5f                   	pop    %rdi
   d:	5d                   	pop    %rbp
   e:	c3                   	ret
   f:	90                   	nop
  10:	83 c4 1c             	add    $0x1c,%esp
  13:	b8                   	.byte 0xb8
  14:	ea                   	(bad)
  15:	ff                   	.byte 0xff
[   19.253229][   T64] RSP: 002b:00000000fffd4f00 EFLAGS: 00000202 ORIG_RAX: 00000000000000c0
[   19.253236][   T64] RAX: 00000000f7db9000 RBX: 00000000f7db9000 RCX: 00000000000da000
[   19.253240][   T64] RDX: 0000000000000001 RSI: 0000000000000812 RDI: 0000000000000000
[   19.253244][   T64] RBP: 00000000000001ce R08: 0000000000000000 R09: 0000000000000000
[   19.253248][   T64] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.253251][   T64] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.253266][   T64]  </TASK>
[   19.256786][   T64] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/64
[ 19.304780][ T64] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.305760][   T64] CPU: 1 UID: 0 PID: 64 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.305774][   T64] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.305782][   T64] Call Trace:
[   19.305787][   T64]  <TASK>
[ 19.305795][ T64] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.305817][ T64] dump_stack (lib/dump_stack.c:130) 
[ 19.305832][ T64] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.305849][ T64] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.305862][ T64] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.305881][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.305903][ T64] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.305921][ T64] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.305931][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.305944][ T64] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.305962][ T64] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.305980][ T64] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.306002][ T64] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.306023][ T64] irqentry_exit_to_user_mode (kernel/entry/common.c:124 include/linux/entry-common.h:330 kernel/entry/common.c:184) 
[ 19.306039][ T64] irqentry_exit (kernel/entry/common.c:287) 
[ 19.306050][ T64] exc_page_fault (arch/x86/mm/fault.c:1536) 
[ 19.306072][ T64] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623) 
[   19.306083][   T64] RIP: 0023:0xf7db80cb
[ 19.306094][ T64] Code: 01 00 00 00 83 c4 08 5b c3 66 90 66 90 66 90 55 53 56 57 31 d2 9c 58 89 c1 35 00 00 20 00 50 9d 9c 58 31 c1 31 c0 8b 74 24 14 <89> 46 08 0f ba e1 15 0f 83 6b 01 00 00 0f a2 89 c7 31 c0 81 fb 47
All code
========
   0:	01 00                	add    %eax,(%rax)
   2:	00 00                	add    %al,(%rax)
   4:	83 c4 08             	add    $0x8,%esp
   7:	5b                   	pop    %rbx
   8:	c3                   	ret
   9:	66 90                	xchg   %ax,%ax
   b:	66 90                	xchg   %ax,%ax
   d:	66 90                	xchg   %ax,%ax
   f:	55                   	push   %rbp
  10:	53                   	push   %rbx
  11:	56                   	push   %rsi
  12:	57                   	push   %rdi
  13:	31 d2                	xor    %edx,%edx
  15:	9c                   	pushf
  16:	58                   	pop    %rax
  17:	89 c1                	mov    %eax,%ecx
  19:	35 00 00 20 00       	xor    $0x200000,%eax
  1e:	50                   	push   %rax
  1f:	9d                   	popf
  20:	9c                   	pushf
  21:	58                   	pop    %rax
  22:	31 c1                	xor    %eax,%ecx
  24:	31 c0                	xor    %eax,%eax
  26:	8b 74 24 14          	mov    0x14(%rsp),%esi
  2a:*	89 46 08             	mov    %eax,0x8(%rsi)		<-- trapping instruction
  2d:	0f ba e1 15          	bt     $0x15,%ecx
  31:	0f 83 6b 01 00 00    	jae    0x1a2
  37:	0f a2                	cpuid
  39:	89 c7                	mov    %eax,%edi
  3b:	31 c0                	xor    %eax,%eax
  3d:	81                   	.byte 0x81
  3e:	fb                   	sti
  3f:	47                   	rex.RXB

Code starting with the faulting instruction
===========================================
   0:	89 46 08             	mov    %eax,0x8(%rsi)
   3:	0f ba e1 15          	bt     $0x15,%ecx
   7:	0f 83 6b 01 00 00    	jae    0x178
   d:	0f a2                	cpuid
   f:	89 c7                	mov    %eax,%edi
  11:	31 c0                	xor    %eax,%eax
  13:	81                   	.byte 0x81
  14:	fb                   	sti
  15:	47                   	rex.RXB
[   19.306104][   T64] RSP: 002b:00000000fffd5bd8 EFLAGS: 00210246
[   19.306115][   T64] RAX: 0000000000000000 RBX: 00000000f7eac684 RCX: 0000000000200000
[   19.306123][   T64] RDX: 0000000000000000 RSI: 00000000f7eb3ad0 RDI: 00000000f7eb3ad0
[   19.306131][   T64] RBP: 00000000f7eac684 R08: 0000000000000000 R09: 0000000000000000
[   19.306138][   T64] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.306145][   T64] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.306175][   T64]  </TASK>
[   19.328981][   T64] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/64
[ 19.329865][ T64] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.330477][   T64] CPU: 1 UID: 0 PID: 64 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.330486][   T64] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.330490][   T64] Call Trace:
[   19.330492][   T64]  <TASK>
[ 19.330495][ T64] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.330508][ T64] dump_stack (lib/dump_stack.c:130) 
[ 19.330516][ T64] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.330525][ T64] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.330531][ T64] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.330541][ T64] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.330553][ T64] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.330564][ T64] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.330569][ T64] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.330576][ T64] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.330586][ T64] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.330595][ T64] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.330606][ T64] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.330618][ T64] irqentry_exit_to_user_mode (kernel/entry/common.c:124 include/linux/entry-common.h:330 kernel/entry/common.c:184) 
[ 19.330626][ T64] irqentry_exit (kernel/entry/common.c:287) 
[ 19.330632][ T64] exc_page_fault (arch/x86/mm/fault.c:1536) 
[ 19.330644][ T64] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623) 
[   19.330650][   T64] RIP: 0023:0xf7a9f4c0
[ 19.330656][ T64] Code: 57 8d 1c 06 e8 21 0d 00 00 83 c4 0c c6 04 03 00 50 57 53 89 eb e8 70 15 00 00 83 c4 1c 89 f0 5b 5e 5f 5d c3 66 90 66 90 66 90 <57> 8b 4c 24 08 66 0f 6e 4c 24 0c 66 0f ef d2 89 cf 66 0f 60 c9 66
All code
========
   0:	57                   	push   %rdi
   1:	8d 1c 06             	lea    (%rsi,%rax,1),%ebx
   4:	e8 21 0d 00 00       	call   0xd2a
   9:	83 c4 0c             	add    $0xc,%esp
   c:	c6 04 03 00          	movb   $0x0,(%rbx,%rax,1)
  10:	50                   	push   %rax
  11:	57                   	push   %rdi
  12:	53                   	push   %rbx
  13:	89 eb                	mov    %ebp,%ebx
  15:	e8 70 15 00 00       	call   0x158a
  1a:	83 c4 1c             	add    $0x1c,%esp
  1d:	89 f0                	mov    %esi,%eax
  1f:	5b                   	pop    %rbx
  20:	5e                   	pop    %rsi
  21:	5f                   	pop    %rdi
  22:	5d                   	pop    %rbp
  23:	c3                   	ret
  24:	66 90                	xchg   %ax,%ax
  26:	66 90                	xchg   %ax,%ax
  28:	66 90                	xchg   %ax,%ax
  2a:*	57                   	push   %rdi		<-- trapping instruction
  2b:	8b 4c 24 08          	mov    0x8(%rsp),%ecx
  2f:	66 0f 6e 4c 24 0c    	movd   0xc(%rsp),%xmm1
  35:	66 0f ef d2          	pxor   %xmm2,%xmm2
  39:	89 cf                	mov    %ecx,%edi
  3b:	66 0f 60 c9          	punpcklbw %xmm1,%xmm1
  3f:	66                   	data16

Code starting with the faulting instruction
===========================================
   0:	57                   	push   %rdi
   1:	8b 4c 24 08          	mov    0x8(%rsp),%ecx
   5:	66 0f 6e 4c 24 0c    	movd   0xc(%rsp),%xmm1
   b:	66 0f ef d2          	pxor   %xmm2,%xmm2
   f:	89 cf                	mov    %ecx,%edi
  11:	66 0f 60 c9          	punpcklbw %xmm1,%xmm1
  15:	66                   	data16
[   19.330662][   T64] RSP: 002b:00000000fffd38cc EFLAGS: 00210246
[   19.330667][   T64] RAX: 0000000000000000 RBX: 00000000565dbdd4 RCX: 00000000fffd49a8
[   19.330671][   T64] RDX: 0000000000000000 RSI: 00000000fffd394c RDI: 000000005799e1f0
[   19.330675][   T64] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   19.330679][   T64] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.330682][   T64] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.330697][   T64]  </TASK>
[   19.332542][   T64] modprobe (64) used greatest stack depth: 25120 bytes left
[   19.344814][   T65] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/65
[ 19.360113][ T65] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.361051][   T65] CPU: 0 UID: 0 PID: 65 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.361065][   T65] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.361071][   T65] Call Trace:
[   19.361074][   T65]  <TASK>
[ 19.361079][ T65] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.361099][ T65] dump_stack (lib/dump_stack.c:130) 
[ 19.361111][ T65] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.361125][ T65] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.361136][ T65] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.361144][ T65] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.361162][ T65] ? lock_is_held (include/linux/lockdep.h:249) 
[ 19.361175][ T65] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.361191][ T65] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.361199][ T65] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.361210][ T65] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.361225][ T65] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.361238][ T65] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.361256][ T65] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.361273][ T65] irqentry_exit_to_user_mode (kernel/entry/common.c:124 include/linux/entry-common.h:330 kernel/entry/common.c:184) 
[ 19.361286][ T65] irqentry_exit (kernel/entry/common.c:287) 
[ 19.361295][ T65] exc_page_fault (arch/x86/mm/fault.c:1536) 
[ 19.361313][ T65] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623) 
[   19.361322][   T65] RIP: 0023:0xf7f7b148
[ 19.361330][ T65] Code: bb 41 ff ff 6f 29 d3 89 04 99 e9 f1 fe ff ff 8b b5 74 ff ff ff 85 f6 74 60 8b 47 30 85 c0 74 03 01 70 04 8b 47 2c 85 c0 74 03 <01> 70 04 8b 47 34 85 c0 74 03 01 70 04 8b 47 38 85 c0 74 03 01 70
All code
========
   0:	bb 41 ff ff 6f       	mov    $0x6fffff41,%ebx
   5:	29 d3                	sub    %edx,%ebx
   7:	89 04 99             	mov    %eax,(%rcx,%rbx,4)
   a:	e9 f1 fe ff ff       	jmp    0xffffffffffffff00
   f:	8b b5 74 ff ff ff    	mov    -0x8c(%rbp),%esi
  15:	85 f6                	test   %esi,%esi
  17:	74 60                	je     0x79
  19:	8b 47 30             	mov    0x30(%rdi),%eax
  1c:	85 c0                	test   %eax,%eax
  1e:	74 03                	je     0x23
  20:	01 70 04             	add    %esi,0x4(%rax)
  23:	8b 47 2c             	mov    0x2c(%rdi),%eax
  26:	85 c0                	test   %eax,%eax
  28:	74 03                	je     0x2d
  2a:*	01 70 04             	add    %esi,0x4(%rax)		<-- trapping instruction
  2d:	8b 47 34             	mov    0x34(%rdi),%eax
  30:	85 c0                	test   %eax,%eax
  32:	74 03                	je     0x37
  34:	01 70 04             	add    %esi,0x4(%rax)
  37:	8b 47 38             	mov    0x38(%rdi),%eax
  3a:	85 c0                	test   %eax,%eax
  3c:	74 03                	je     0x41
  3e:	01                   	.byte 0x1
  3f:	70                   	.byte 0x70

Code starting with the faulting instruction
===========================================
   0:	01 70 04             	add    %esi,0x4(%rax)
   3:	8b 47 34             	mov    0x34(%rdi),%eax
   6:	85 c0                	test   %eax,%eax
   8:	74 03                	je     0xd
   a:	01 70 04             	add    %esi,0x4(%rax)
   d:	8b 47 38             	mov    0x38(%rdi),%eax
  10:	85 c0                	test   %eax,%eax
  12:	74 03                	je     0x17
  14:	01                   	.byte 0x1
  15:	70                   	.byte 0x70
[   19.361339][   T65] RSP: 002b:00000000ffdeddc0 EFLAGS: 00010286
[   19.361348][   T65] RAX: 00000000f7f395e4 RBX: 0000000000000028 RCX: 00000000f7f6d310
[   19.361355][   T65] RDX: 0000000000000000 RSI: 00000000f7c78000 RDI: 00000000f7f6d2f0
[   19.361361][   T65] RBP: 00000000ffdedea8 R08: 0000000000000000 R09: 0000000000000000
[   19.361367][   T65] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.361372][   T65] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.361395][   T65]  </TASK>
[   19.405251][   T65] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/65
[ 19.406850][ T65] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.407947][   T65] CPU: 0 UID: 0 PID: 65 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.407964][   T65] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.407972][   T65] Call Trace:
[   19.407977][   T65]  <TASK>
[ 19.407984][ T65] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.408010][ T65] dump_stack (lib/dump_stack.c:130) 
[ 19.408027][ T65] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.408048][ T65] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.408062][ T65] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.408083][ T65] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.408108][ T65] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.408130][ T65] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.408141][ T65] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.408155][ T65] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.408182][ T65] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.408198][ T65] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.408211][ T65] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.408225][ T65] irqentry_exit_to_user_mode (kernel/entry/common.c:124 include/linux/entry-common.h:330 kernel/entry/common.c:184) 
[ 19.408235][ T65] irqentry_exit (kernel/entry/common.c:287) 
[ 19.408242][ T65] exc_page_fault (arch/x86/mm/fault.c:1536) 
[ 19.408256][ T65] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623) 
[   19.408264][   T65] RIP: 0023:0xf7b9cca0
[ 19.408271][ T65] Code: 04 00 00 00 c7 44 24 2c 03 00 00 00 e9 3a fe ff ff e8 a4 1e 00 00 66 90 66 90 c3 66 90 66 90 66 90 66 90 66 90 66 90 66 90 90 <e8> 14 01 03 00 05 5b 73 0d 00 53 8b 88 f4 fe ff ff 8d 90 e0 38 f6
All code
========
   0:	04 00                	add    $0x0,%al
   2:	00 00                	add    %al,(%rax)
   4:	c7 44 24 2c 03 00 00 	movl   $0x3,0x2c(%rsp)
   b:	00 
   c:	e9 3a fe ff ff       	jmp    0xfffffffffffffe4b
  11:	e8 a4 1e 00 00       	call   0x1eba
  16:	66 90                	xchg   %ax,%ax
  18:	66 90                	xchg   %ax,%ax
  1a:	c3                   	ret
  1b:	66 90                	xchg   %ax,%ax
  1d:	66 90                	xchg   %ax,%ax
  1f:	66 90                	xchg   %ax,%ax
  21:	66 90                	xchg   %ax,%ax
  23:	66 90                	xchg   %ax,%ax
  25:	66 90                	xchg   %ax,%ax
  27:	66 90                	xchg   %ax,%ax
  29:	90                   	nop
  2a:*	e8 14 01 03 00       	call   0x30143		<-- trapping instruction
  2f:	05 5b 73 0d 00       	add    $0xd735b,%eax
  34:	53                   	push   %rbx
  35:	8b 88 f4 fe ff ff    	mov    -0x10c(%rax),%ecx
  3b:	8d                   	.byte 0x8d
  3c:	90                   	nop
  3d:	e0 38                	loopne 0x77
  3f:	f6                   	.byte 0xf6

Code starting with the faulting instruction
===========================================
   0:	e8 14 01 03 00       	call   0x30119
   5:	05 5b 73 0d 00       	add    $0xd735b,%eax
   a:	53                   	push   %rbx
   b:	8b 88 f4 fe ff ff    	mov    -0x10c(%rax),%ecx
  11:	8d                   	.byte 0x8d
  12:	90                   	nop
  13:	e0 38                	loopne 0x4d
  15:	f6                   	.byte 0xf6
[   19.408277][   T65] RSP: 002b:00000000ffdee69c EFLAGS: 00010202
[   19.408285][   T65] RAX: 0000000000000000 RBX: 0000000000000007 RCX: 00000000f7f6d5d0
[   19.408289][   T65] RDX: 0000000000000015 RSI: 00000000f7c81904 RDI: 00000000f7b9cca0
[   19.408294][   T65] RBP: 00000000ffdee738 R08: 0000000000000000 R09: 0000000000000000
[   19.408299][   T65] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.408303][   T65] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.408320][   T65]  </TASK>
[   19.430721][   T65] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/65
[ 19.431596][ T65] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.432219][   T65] CPU: 0 UID: 0 PID: 65 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.432227][   T65] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.432232][   T65] Call Trace:
[   19.432234][   T65]  <TASK>
[ 19.432237][ T65] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.432250][ T65] dump_stack (lib/dump_stack.c:130) 
[ 19.432258][ T65] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.432267][ T65] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.432274][ T65] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.432283][ T65] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.432295][ T65] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.432306][ T65] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.432311][ T65] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.432318][ T65] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.432327][ T65] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.432336][ T65] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.432348][ T65] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.432359][ T65] exit_to_user_mode_loop (kernel/entry/common.c:124) 
[ 19.432367][ T65] do_int80_emulation (include/linux/entry-common.h:332 include/linux/entry-common.h:414 include/linux/entry-common.h:449 arch/x86/entry/syscall_32.c:175) 
[ 19.432375][ T65] ? rcu_read_unlock (include/linux/rcupdate.h:874 (discriminator 9)) 
[ 19.432381][ T65] ? do_read_fault (mm/memory.c:5600) 
[ 19.432394][ T65] ? do_pte_missing (mm/memory.c:4252) 
[ 19.432401][ T65] ? handle_pte_fault (mm/memory.c:6069) 
[ 19.432412][ T65] ? handle_pte_fault (mm/memory.c:6026) 
[ 19.432421][ T65] ? __pfx_handle_pte_fault (mm/memory.c:6026) 
[ 19.432430][ T65] ? validate_chain (kernel/locking/lockdep.c:3826 kernel/locking/lockdep.c:3879) 
[ 19.432439][ T65] ? validate_chain (kernel/locking/lockdep.c:3826 kernel/locking/lockdep.c:3879) 
[ 19.432449][ T65] ? __lock_acquire (kernel/locking/lockdep.c:5240) 
[ 19.432461][ T65] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.432471][ T65] ? vtime_user_exit (kernel/sched/cputime.c:737) 
[ 19.432482][ T65] ? vtime_user_exit (kernel/sched/cputime.c:737) 
[ 19.432492][ T65] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.432504][ T65] ? debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.432510][ T65] ? rcu_is_watching (include/linux/context_tracking.h:128 kernel/rcu/tree.c:745) 
[ 19.432519][ T65] ? trace_irq_disable (include/trace/events/preemptirq.h:36 (discriminator 21)) 
[ 19.432529][ T65] ? trace_hardirqs_off_finish (kernel/trace/trace_preemptirq.c:98) 
[ 19.432537][ T65] ? do_int80_emulation (arch/x86/include/asm/jump_label.h:36 arch/x86/entry/syscall_32.c:148) 
[ 19.432546][ T65] asm_int80_emulation (arch/x86/include/asm/idtentry.h:626) 
[   19.432552][   T65] RIP: 0023:0xf7f8fd24
[ 19.432558][ T65] Code: b8 5b 00 00 00 cd 80 89 d3 3d 01 f0 ff ff 0f 83 b2 ef ff ff c3 90 53 8b 54 24 10 8b 4c 24 0c 8b 5c 24 08 b8 7d 00 00 00 cd 80 <5b> 3d 01 f0 ff ff 0f 83 90 ef ff ff c3 66 90 66 90 66 90 66 90 66
All code
========
   0:	b8 5b 00 00 00       	mov    $0x5b,%eax
   5:	cd 80                	int    $0x80
   7:	89 d3                	mov    %edx,%ebx
   9:	3d 01 f0 ff ff       	cmp    $0xfffff001,%eax
   e:	0f 83 b2 ef ff ff    	jae    0xffffffffffffefc6
  14:	c3                   	ret
  15:	90                   	nop
  16:	53                   	push   %rbx
  17:	8b 54 24 10          	mov    0x10(%rsp),%edx
  1b:	8b 4c 24 0c          	mov    0xc(%rsp),%ecx
  1f:	8b 5c 24 08          	mov    0x8(%rsp),%ebx
  23:	b8 7d 00 00 00       	mov    $0x7d,%eax
  28:	cd 80                	int    $0x80
  2a:*	5b                   	pop    %rbx		<-- trapping instruction
  2b:	3d 01 f0 ff ff       	cmp    $0xfffff001,%eax
  30:	0f 83 90 ef ff ff    	jae    0xffffffffffffefc6
  36:	c3                   	ret
  37:	66 90                	xchg   %ax,%ax
  39:	66 90                	xchg   %ax,%ax
  3b:	66 90                	xchg   %ax,%ax
  3d:	66 90                	xchg   %ax,%ax
  3f:	66                   	data16

Code starting with the faulting instruction
===========================================
   0:	5b                   	pop    %rbx
   1:	3d 01 f0 ff ff       	cmp    $0xfffff001,%eax
   6:	0f 83 90 ef ff ff    	jae    0xffffffffffffef9c
   c:	c3                   	ret
   d:	66 90                	xchg   %ax,%ax
   f:	66 90                	xchg   %ax,%ax
  11:	66 90                	xchg   %ax,%ax
  13:	66 90                	xchg   %ax,%ax
  15:	66                   	data16
[   19.432564][   T65] RSP: 002b:00000000ffdee668 EFLAGS: 00000206 ORIG_RAX: 000000000000007d
[   19.432571][   T65] RAX: 0000000000000000 RBX: 00000000f7f21000 RCX: 000000000001b000
[   19.432575][   T65] RDX: 0000000000000001 RSI: 00000000f7f9e000 RDI: 00000000f7f6d2f0
[   19.432579][   T65] RBP: 00000000ffdee738 R08: 0000000000000000 R09: 0000000000000000
[   19.432583][   T65] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.432586][   T65] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.432601][   T65]  </TASK>
[   19.477057][   T66] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/66
[ 19.481747][ T66] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.484904][   T66] CPU: 1 UID: 0 PID: 66 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.484945][   T66] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.484963][   T66] Call Trace:
[   19.484975][   T66]  <TASK>
[ 19.484991][ T66] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.485052][ T66] dump_stack (lib/dump_stack.c:130) 
[ 19.485092][ T66] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.485139][ T66] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.485176][ T66] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.485202][ T66] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.485264][ T66] ? lock_is_held (include/linux/lockdep.h:249) 
[ 19.485307][ T66] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.485357][ T66] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.485384][ T66] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.485418][ T66] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.485468][ T66] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.485513][ T66] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.485550][ T66] ? preempt_latency_start (include/linux/ftrace.h:1091 kernel/sched/core.c:5866) 
[ 19.485607][ T66] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.485660][ T66] exit_to_user_mode_loop (kernel/entry/common.c:124) 
[ 19.485700][ T66] do_int80_emulation (include/linux/entry-common.h:332 include/linux/entry-common.h:414 include/linux/entry-common.h:449 arch/x86/entry/syscall_32.c:175) 
[ 19.485758][ T66] ? __lock_acquire (kernel/locking/lockdep.c:5240) 
[ 19.485821][ T66] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.485871][ T66] ? vtime_user_exit (kernel/sched/cputime.c:737) 
[ 19.485924][ T66] ? vtime_user_exit (kernel/sched/cputime.c:737) 
[ 19.485976][ T66] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.486035][ T66] ? debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.486070][ T66] ? rcu_is_watching (include/linux/context_tracking.h:128 kernel/rcu/tree.c:745) 
[ 19.486111][ T66] ? trace_irq_disable (include/trace/events/preemptirq.h:36 (discriminator 21)) 
[ 19.486159][ T66] ? trace_hardirqs_off_finish (kernel/trace/trace_preemptirq.c:98) 
[ 19.486198][ T66] ? do_int80_emulation (arch/x86/include/asm/jump_label.h:36 arch/x86/entry/syscall_32.c:148) 
[ 19.486244][ T66] asm_int80_emulation (arch/x86/include/asm/idtentry.h:626) 
[   19.486274][   T66] RIP: 0023:0xf7f82cb0
[ 19.486300][ T66] Code: 4c 24 34 89 44 24 0c 8b 44 24 44 8b 54 24 38 8b 74 24 3c 8b 7c 24 40 a9 ff 0f 00 00 75 1c c1 e8 0c 89 c5 b8 c0 00 00 00 cd 80 <3d> 00 f0 ff ff 77 21 83 c4 1c 5b 5e 5f 5d c3 90 83 c4 1c b8 ea ff
All code
========
   0:	4c 24 34             	rex.WR and $0x34,%al
   3:	89 44 24 0c          	mov    %eax,0xc(%rsp)
   7:	8b 44 24 44          	mov    0x44(%rsp),%eax
   b:	8b 54 24 38          	mov    0x38(%rsp),%edx
   f:	8b 74 24 3c          	mov    0x3c(%rsp),%esi
  13:	8b 7c 24 40          	mov    0x40(%rsp),%edi
  17:	a9 ff 0f 00 00       	test   $0xfff,%eax
  1c:	75 1c                	jne    0x3a
  1e:	c1 e8 0c             	shr    $0xc,%eax
  21:	89 c5                	mov    %eax,%ebp
  23:	b8 c0 00 00 00       	mov    $0xc0,%eax
  28:	cd 80                	int    $0x80
  2a:*	3d 00 f0 ff ff       	cmp    $0xfffff000,%eax		<-- trapping instruction
  2f:	77 21                	ja     0x52
  31:	83 c4 1c             	add    $0x1c,%esp
  34:	5b                   	pop    %rbx
  35:	5e                   	pop    %rsi
  36:	5f                   	pop    %rdi
  37:	5d                   	pop    %rbp
  38:	c3                   	ret
  39:	90                   	nop
  3a:	83 c4 1c             	add    $0x1c,%esp
  3d:	b8                   	.byte 0xb8
  3e:	ea                   	(bad)
  3f:	ff                   	.byte 0xff

Code starting with the faulting instruction
===========================================
   0:	3d 00 f0 ff ff       	cmp    $0xfffff000,%eax
   5:	77 21                	ja     0x28
   7:	83 c4 1c             	add    $0x1c,%esp
   a:	5b                   	pop    %rbx
   b:	5e                   	pop    %rsi
   c:	5f                   	pop    %rdi
   d:	5d                   	pop    %rbp
   e:	c3                   	ret
   f:	90                   	nop
  10:	83 c4 1c             	add    $0x1c,%esp
  13:	b8                   	.byte 0xb8
  14:	ea                   	(bad)
  15:	ff                   	.byte 0xff
[   19.486327][   T66] RSP: 002b:00000000ff907830 EFLAGS: 00000246 ORIG_RAX: 00000000000000c0
[   19.486359][   T66] RAX: 00000000f7f34000 RBX: 0000000000000000 RCX: 000000000002b148
[   19.486380][   T66] RDX: 0000000000000001 RSI: 0000000000000802 RDI: 0000000000000000
[   19.486399][   T66] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   19.486418][   T66] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.486437][   T66] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.486519][   T66]  </TASK>
[   19.544246][   T66] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/66
[ 19.545273][ T66] caller is debug_smp_processor_id (lib/smp_processor_id.c:61) 
[   19.545971][   T66] CPU: 1 UID: 0 PID: 66 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
[   19.545981][   T66] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   19.545985][   T66] Call Trace:
[   19.545988][   T66]  <TASK>
[ 19.545992][ T66] dump_stack_lvl (lib/dump_stack.c:123) 
[ 19.546007][ T66] dump_stack (lib/dump_stack.c:130) 
[ 19.546016][ T66] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53) 
[ 19.546027][ T66] debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.546035][ T66] task_cache_work (kernel/sched/fair.c:1422) 
[ 19.546046][ T66] ? find_held_lock (kernel/locking/lockdep.c:5353) 
[ 19.546060][ T66] ? _raw_spin_unlock_irq (arch/x86/include/asm/paravirt.h:671 include/linux/spinlock_api_smp.h:159 kernel/locking/spinlock.c:202) 
[ 19.546072][ T66] ? __pfx_task_cache_work (kernel/sched/fair.c:1416) 
[ 19.546078][ T66] ? __this_cpu_preempt_check (lib/smp_processor_id.c:67) 
[ 19.546086][ T66] ? lockdep_hardirqs_on (kernel/locking/lockdep.c:4475) 
[ 19.546098][ T66] task_work_run (kernel/task_work.c:228 (discriminator 1)) 
[ 19.546108][ T66] ? __pfx_task_work_run (kernel/task_work.c:195) 
[ 19.546122][ T66] resume_user_mode_work (arch/x86/include/asm/current.h:25 include/linux/resume_user_mode.h:53) 
[ 19.546135][ T66] exit_to_user_mode_loop (kernel/entry/common.c:124) 
[ 19.546144][ T66] do_int80_emulation (include/linux/entry-common.h:332 include/linux/entry-common.h:414 include/linux/entry-common.h:449 arch/x86/entry/syscall_32.c:175) 
[ 19.546155][ T66] ? debug_smp_processor_id (lib/smp_processor_id.c:61) 
[ 19.546163][ T66] ? rcu_is_watching (include/linux/context_tracking.h:128 kernel/rcu/tree.c:745) 
[ 19.546173][ T66] ? trace_irq_disable (include/trace/events/preemptirq.h:36 (discriminator 21)) 
[ 19.546184][ T66] ? trace_hardirqs_off_finish (kernel/trace/trace_preemptirq.c:98) 
[ 19.546193][ T66] ? do_int80_emulation (arch/x86/include/asm/jump_label.h:36 arch/x86/entry/syscall_32.c:148) 
[ 19.546203][ T66] asm_int80_emulation (arch/x86/include/asm/idtentry.h:626) 
[   19.546211][   T66] RIP: 0023:0xf7f82cb0
[ 19.546218][ T66] Code: 4c 24 34 89 44 24 0c 8b 44 24 44 8b 54 24 38 8b 74 24 3c 8b 7c 24 40 a9 ff 0f 00 00 75 1c c1 e8 0c 89 c5 b8 c0 00 00 00 cd 80 <3d> 00 f0 ff ff 77 21 83 c4 1c 5b 5e 5f 5d c3 90 83 c4 1c b8 ea ff
All code
========
   0:	4c 24 34             	rex.WR and $0x34,%al
   3:	89 44 24 0c          	mov    %eax,0xc(%rsp)
   7:	8b 44 24 44          	mov    0x44(%rsp),%eax
   b:	8b 54 24 38          	mov    0x38(%rsp),%edx
   f:	8b 74 24 3c          	mov    0x3c(%rsp),%esi
  13:	8b 7c 24 40          	mov    0x40(%rsp),%edi
  17:	a9 ff 0f 00 00       	test   $0xfff,%eax
  1c:	75 1c                	jne    0x3a
  1e:	c1 e8 0c             	shr    $0xc,%eax
  21:	89 c5                	mov    %eax,%ebp
  23:	b8 c0 00 00 00       	mov    $0xc0,%eax
  28:	cd 80                	int    $0x80
  2a:*	3d 00 f0 ff ff       	cmp    $0xfffff000,%eax		<-- trapping instruction
  2f:	77 21                	ja     0x52
  31:	83 c4 1c             	add    $0x1c,%esp
  34:	5b                   	pop    %rbx
  35:	5e                   	pop    %rsi
  36:	5f                   	pop    %rdi
  37:	5d                   	pop    %rbp
  38:	c3                   	ret
  39:	90                   	nop
  3a:	83 c4 1c             	add    $0x1c,%esp
  3d:	b8                   	.byte 0xb8
  3e:	ea                   	(bad)
  3f:	ff                   	.byte 0xff

Code starting with the faulting instruction
===========================================
   0:	3d 00 f0 ff ff       	cmp    $0xfffff000,%eax
   5:	77 21                	ja     0x28
   7:	83 c4 1c             	add    $0x1c,%esp
   a:	5b                   	pop    %rbx
   b:	5e                   	pop    %rsi
   c:	5f                   	pop    %rdi
   d:	5d                   	pop    %rbp
   e:	c3                   	ret
   f:	90                   	nop
  10:	83 c4 1c             	add    $0x1c,%esp
  13:	b8                   	.byte 0xb8
  14:	ea                   	(bad)
  15:	ff                   	.byte 0xff
[   19.546225][   T66] RSP: 002b:00000000ff907810 EFLAGS: 00000246 ORIG_RAX: 00000000000000c0
[   19.546233][   T66] RAX: 00000000f7c6b000 RBX: 0000000000000000 RCX: 00000000002c8ae0
[   19.546238][   T66] RDX: 0000000000000001 RSI: 0000000000000802 RDI: 0000000000000000
[   19.546243][   T66] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   19.546247][   T66] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   19.546252][   T66] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   19.546269][   T66]  </TASK>


The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20250812/202508120315.19f6266a-lkp@intel.com



-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [RFC PATCH v4 01/28] sched: Cache aware load-balancing

[Chen, Yu C]

Hi,

On 8/12/2025 9:30 AM, kernel test robot wrote:
> [ 18.146207][ T63] RIP: 0010:_find_next_bit (kbuild/src/consumer/lib/find_bit.c:156 (discriminator 2))
> [ 18.146207][ T63] task_cache_work (kbuild/src/consumer/include/linux/find.h:71 (discriminator 2)
> kbuild/src/consumer/kernel/sched/fair.c:1325 (discriminator 2))

This should have been fixed in the second patch:
02/28 ("sched: Several fixes for cache aware scheduling")that the LLC 
sched domain could be NULL and we should skip the
NULL LLC sched domain.

It might be more applicable to test with the whole patch set.
As this is a RFC version and we will create a formal one with
the fixes integrated into the 01/28 patch, after the issues
have been addressed.

thanks,
Chenyu

Re: [RFC PATCH v4 23/28] sched: Scan a task's preferred node for preferred LLC

[Chen, Yu C]

On 8/12/2025 9:59 AM, kernel test robot wrote:
> 
> 
> [   19.177186][   T64] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/64
> [ 19.179622][ T64] caller is debug_smp_processor_id (lib/smp_processor_id.c:61)
> [   19.181347][   T64] CPU: 0 UID: 0 PID: 64 Comm: modprobe Not tainted 6.16.0-00023-gff797757d658 #1 PREEMPT(none)
> [   19.181372][   T64] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [   19.181385][   T64] Call Trace:
> [   19.181391][   T64]  <TASK>
> [ 19.181401][ T64] dump_stack_lvl (lib/dump_stack.c:123)
> [ 19.181440][ T64] dump_stack (lib/dump_stack.c:130)
> [ 19.181465][ T64] check_preemption_disabled (arch/x86/include/asm/preempt.h:85 lib/smp_processor_id.c:53)
> [ 19.181494][ T64] debug_smp_processor_id (lib/smp_processor_id.c:61)
> [ 19.181514][ T64] task_cache_work (kernel/sched/fair.c:1422)

Thanks for the report, will use get_cpu() in next version.

thanks,
Chenyu

Re: [RFC PATCH v4 25/28] sched: Skip cache aware scheduling if the process has many active threads

[Tingyin Duan]

Re: [RFC PATCH v4 25/28] sched: Skip cache aware scheduling if the process has many active threads

[Tingyin Duan]

Several different test cases with mysql and sysbench shows that this patch causes about 10% performance regressions on my computer with 256 cores. Perf-top shows exceed_llc_nr is high. Could you help to address this problems ?

Re: [RFC PATCH v4 25/28] sched: Skip cache aware scheduling if the process has many active threads

[Chen, Yu C]

On 9/2/2025 1:16 PM, Tingyin Duan wrote:
> Several different test cases with mysql and sysbench shows that this patch
> causes about 10% performance regressions on my computer with 256 cores.
> Perf-top shows exceed_llc_nr is high. Could you help to address this problems?

Thanks for bringing this to public for discussion. As we synced offline, the
performance regression is likely to be caused by the cache contention 
introduced
by the [25/28] patch:

The 1st issue:Multiple threads within the same process try to read the 
mm_struct->nr_running_avg
while the task_cache_work() modifies the mm_struct->mm_sched_cpu from 
time to time.
Since the mm_sched_cpu and nr_running_avg are in the same cacheline, 
this update
turns the cacheline into "Modified" and the read triggers the costly 
"HITM" event.
We should move nr_running_avg and mm_sched_cpu to different cachelines.

The 2nd issue:
If nr_running_avg remains consistently above the threshold in your test 
case,
exceed_llc_nr() will always return true. This might cause the frequent 
write of -1
to mm->mm_sched_cpu, even if mm->mm_sched_cpu is already -1. This causes 
another
cache contention that threads on other CPUs trying to read the 
mm->mm_sched_cpu.
We should update the mm_struct's mm_sched_cpu field only if the value 
has been
changed.

That is to say, the following patch should fix the regression:

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 2cca039d6e4f..3c1c50134647 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1032,7 +1032,11 @@ struct mm_struct {
  		raw_spinlock_t mm_sched_lock;
  		unsigned long mm_sched_epoch;
  		int mm_sched_cpu;
-		u64 nr_running_avg;
+		/*
+		 * mm_sched_cpu and nr_running_avg are put into seperate
+		 * cachelines to avoid cache contention.
+		 */
+		u64 nr_running_avg ____cacheline_aligned_in_smp;
  #endif

  #ifdef CONFIG_MMU
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 026013c826d9..4ef28db57a37 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1428,7 +1428,8 @@ void account_mm_sched(struct rq *rq, struct 
task_struct *p, s64 delta_exec)
  	    get_nr_threads(p) <= 1 ||
  	    exceed_llc_nr(mm, cpu_of(rq)) ||
  	    exceed_llc_capacity(mm, cpu_of(rq))) {
-		mm->mm_sched_cpu = -1;
+		if (mm->mm_sched_cpu != -1)
+			mm->mm_sched_cpu = -1;
  		pcpu_sched->occ = 0;
  	}

-- 
2.25.1


With above change, the regression I mentioned in the cover letter, when
running multiple instances of hackbench on AMD Milan has disappeared.
And max latency improvement of sysbench+MariaDB are observed on Milan:
transactions per sec.: -0.72%
min latency: -0.00%
avg latency: -0.00%
max latency: +78.90%
95th percentile: -0.00%
events avg: -0.72%
events stddev: +50.72%

thanks,
Chenyu

Re: [RFC PATCH v4 25/28] sched: Skip cache aware scheduling if the process has many active threads

[Duan Tingyin]

After applying this patch, the performance regression has been significantly improved. Thank you!