[PATCH 2/6] x86,sched: Add support for frequency invariance on SKYLAKE_X

Giovanni Gherdovich
2019-11-11T18:00:28Z

The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
accounting. On SKYLAKE_X CPUs set freq_max to the highest frequency that can
be sustained by a group of at least 4 cores.

From the changelog of commit 31e07522be56 ("tools/power turbostat: fix
decoding for GLM, DNV, SKX turbo-ratio limits"):

> Newer processors do not hard-code the the number of cpus in each bin
> to {1, 2, 3, 4, 5, 6, 7, 8} Rather, they can specify any number
> of CPUS in each of the 8 bins:
>
> eg.
>
> ...
> 37 * 100.0 = 3600.0 MHz max turbo 4 active cores
> 38 * 100.0 = 3700.0 MHz max turbo 3 active cores
> 39 * 100.0 = 3800.0 MHz max turbo 2 active cores
> 39 * 100.0 = 3900.0 MHz max turbo 1 active cores
>
> could now look something like this:
>
> ...
> 37 * 100.0 = 3600.0 MHz max turbo 16 active cores
> 38 * 100.0 = 3700.0 MHz max turbo 8 active cores
> 39 * 100.0 = 3800.0 MHz max turbo 4 active cores
> 39 * 100.0 = 3900.0 MHz max turbo 2 active cores

This encoding of turbo levels applies to both SKYLAKE_X and GOLDMONT/GOLDMONT_D,
but we treat these two classes in separate commits because their freq_max
values need to be different. For SKX we prefer a lower freq_max in the ratio
freq_curr/freq_max, allowing load and utilization to overshoot and the
schedutil governor to be more performance-oriented. Models from the Atom
series (such as GOLDMONT*) are handled in a forthcoming commit as they have to
favor power-efficiency over performance.

Results from a performance evaluation follow.

1. TEST SETUP
2. NEUTRAL BENCHMARKS
3. NON-NEUTRAL BENCHMARKS
4. DETAILED TABLES

1. TEST SETUP
-------------

Test machine:

CPU Model : Intel Xeon Platinum 8260L CPU @ 2.40GHz (a.k.a. Cascade Lake)
Fam/Mod/Ste : 6:85:6
Topology : 2 sockets, 24 cores / 48 threads each socket
Memory : 192G
Storage : SSD, XFS filesystem

Max EFFICiency, BASE frequency and available turbo levels (MHz):

EFFIC 1000 |**********
BASE 2400 |************************
24C 3100 |*******************************
20C 3300 |*********************************
16C 3600 |************************************
12C 3600 |************************************
8C 3600 |************************************
4C 3700 |*************************************
2C 3900 |***************************************

Tested kernels:

Baseline : v5.2, intel_pstate passive, schedutil
Comparison #1 : v5.2, intel_pstate active , powersave+HWP
Comparison #2 : v5.2, this patch, intel_pstate passive, schedutil

2. NEUTRAL BENCHMARKS
---------------------

* pgbench read/write
* NASA Parallel Benchmarks (NPB), MPI or OpenMP for message-passing
* hackbench
* netperf

3. NON-NEUTRAL BENCHMARKS
-------------------------

comparison ratio with baseline; 1.00 means neutral, higher is better:

I_PSTATE FREQ-INV
----------------------------------------
pgbench read-only 1.10 ~
tbench 1.82 1.14

comparison ratio with baseline; 1.00 means neutral, lower is better:

I_PSTATE FREQ-INV
----------------------------------------
dbench ~ 0.97
kernbench 0.88 0.78
gitsource[*] ~ 0.46

[*] "gitsource" consists in running git's unit tests
tilde (~) means 1.00, ie result identical to baseline

Performance per watt:

performance-per-watt ratios with baseline; 1.00 means neutral, higher is better:

I_PSTATE FREQ-INV
----------------------------------------
dbench 0.92 0.91
tbench 1.26 1.04
kernbench 0.95 0.96
gitsource 1.03 1.30

Similarly to earlier Xeons, measurable performance gains over non-invariant
schedutil are observed on dbench, tbench, kernel compilation and running the
git unit tests suite. Looking at the detailed tables show that the patch
scores the largest difference when the machine is lightly loaded. Power
efficiency suffers lightly on kernbench and a bit more on dbench, but largely
improves on gitsource (which also runs considerably faster). For reference, we
also report results using active intel_pstate with powersave and HWP; the
largest gap between non-invariant schedutil and intel_pstate+powersave is
still tbench, which runs 82% better and with 26% improved efficiency on the
latter configuration -- this divide isn't closed yet by frequency-invariant
schedutil.

4. DETAILED TABLES
------------------

Benchmark : tbench4 (i.e. dbench4 over the network, actually loopback)
Varying parameter : number of clients
Unit : MB/sec (higher is better)

5.2.0 vanilla (BASELINE) 5.2.0 intel_pstate/HWP 5.2.0 freq-inv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Hmean 1 183.56 +- 0.21% ( ) 516.12 +- 0.57% ( 181.18%) 185.59 +- 0.59% ( 1.11%)
Hmean 2 365.75 +- 0.25% ( ) 1015.14 +- 0.33% ( 177.55%) 402.59 +- 4.48% ( 10.07%)
Hmean 4 720.99 +- 0.44% ( ) 1951.75 +- 0.28% ( 170.70%) 738.39 +- 1.72% ( 2.41%)
Hmean 8 1449.93 +- 0.34% ( ) 3830.56 +- 0.24% ( 164.19%) 1750.36 +- 4.65% ( 20.72%)
Hmean 16 2874.26 +- 0.57% ( ) 7381.62 +- 0.53% ( 156.82%) 4348.35 +- 2.22% ( 51.29%)
Hmean 32 6116.17 +- 5.10% ( ) 13013.05 +- 0.08% ( 112.76%) 8980.35 +- 0.66% ( 46.83%)
Hmean 64 14485.04 +- 3.46% ( ) 17835.12 +- 0.35% ( 23.13%) 16540.73 +- 0.51% ( 14.19%)
Hmean 128 30779.16 +- 3.20% ( ) 32796.94 +- 2.13% ( 6.56%) 31512.58 +- 0.20% ( 2.38%)
Hmean 256 34664.66 +- 0.81% ( ) 34604.67 +- 0.46% ( -0.17%) 34943.70 +- 0.25% ( 0.80%)
Hmean 384 33957.51 +- 0.11% ( ) 34091.50 +- 0.14% ( 0.39%) 33921.41 +- 0.09% ( -0.11%)

Benchmark : kernbench (kernel compilation)
Varying parameter : number of jobs
Unit : seconds (lower is better)

5.2.0 vanilla (BASELINE) 5.2.0 intel_pstate/HWP 5.2.0 freq-inv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Amean 2 332.94 +- 0.40% ( ) 260.16 +- 0.45% ( 21.86%) 233.56 +- 0.21% ( 29.85%)
Amean 4 173.04 +- 0.43% ( ) 138.76 +- 0.03% ( 19.81%) 123.59 +- 0.11% ( 28.58%)
Amean 8 89.65 +- 0.20% ( ) 73.54 +- 0.09% ( 17.97%) 65.69 +- 0.10% ( 26.72%)
Amean 16 48.08 +- 1.41% ( ) 41.64 +- 1.61% ( 13.40%) 36.00 +- 1.80% ( 25.11%)
Amean 32 28.78 +- 0.72% ( ) 26.61 +- 1.99% ( 7.55%) 23.19 +- 1.68% ( 19.43%)
Amean 64 20.46 +- 1.85% ( ) 19.76 +- 0.35% ( 3.42%) 17.38 +- 0.92% ( 15.06%)
Amean 128 18.69 +- 1.70% ( ) 17.59 +- 1.04% ( 5.90%) 15.73 +- 1.40% ( 15.85%)
Amean 192 18.82 +- 1.01% ( ) 17.76 +- 0.77% ( 5.67%) 15.57 +- 1.80% ( 17.28%)

Benchmark : gitsource (time to run the git unit test suite)
Varying parameter : none
Unit : seconds (lower is better)

5.2.0 vanilla (BASELINE) 5.2.0 intel_pstate/HWP 5.2.0 freq-inv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Amean 792.49 +- 0.20% ( ) 779.35 +- 0.24% ( 1.66%) 427.14 +- 0.16% ( 46.10%)

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
---
arch/x86/kernel/smpboot.c | 79 +++++++++++++++++++++++++++++++++++++++--------
1 file changed, 66 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 814d7900779d..11d57d741584 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1841,23 +1841,71 @@ static const struct x86_cpu_id has_glm_turbo_ratio_limits[] = {
{}
};

-static void core_set_cpu_max_freq(void)
+static int get_turbo_ratio_group(u64 *turbo_ratio)
+{
+ u64 ratio, core_counts;
+ u32 group_size = 0;
+ int err, i, found = 0;
+
+ err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &ratio);
+ if (err)
+ return err;
+
+ err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT1, &core_counts);
+ if (err)
+ return err;
+
+ for (i = 0; i < 64; i += 8) {
+ group_size = (core_counts >> i) & 0xFF;
+ if (group_size >= 4) {
+ *turbo_ratio = (ratio >> i) & 0xFF;
+ found = 1;
+ break;
+ }
+ }
+
+ if (!found)
+ return 1;
+
+ return 0;
+}
+
+static bool skx_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
{
- u64 ratio, turbo_ratio;
int err;

- err = rdmsrl_safe(MSR_PLATFORM_INFO, &ratio);
+ if (!x86_match_cpu(has_skx_turbo_ratio_limits))
+ return false;
+
+ err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
if (err)
- return;
+ return false;

- err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &turbo_ratio);
+ err = get_turbo_ratio_group(turbo_ratio); /* 4C (circa) turbo ratio */
if (err)
- return;
+ return false;

- ratio = (ratio >> 8) & 0xFF; /* max P state ratio */
- turbo_ratio = (turbo_ratio >> 24) & 0xFF; /* 4C turbo ratio */
+ *ratio = (*ratio >> 8) & 0xFF; /* max P state ratio */

- arch_max_freq = div_u64(turbo_ratio * SCHED_CAPACITY_SCALE, ratio);
+ return true;
+}
+
+static bool core_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
+{
+ int err;
+
+ err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
+ if (err)
+ return false;
+
+ err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, turbo_ratio);
+ if (err)
+ return false;
+
+ *ratio = (*ratio >> 8) & 0xFF; /* max P state ratio */
+ *turbo_ratio = (*turbo_ratio >> 24) & 0xFF; /* 4C turbo ratio */
+
+ return true;
}

static void intel_set_cpu_max_freq(void)
@@ -1865,7 +1913,6 @@ static void intel_set_cpu_max_freq(void)
/*
* TODO: add support for:
*
- * - Xeon Gold/Platinum
* - Xeon Phi (KNM, KNL)
* - Atom Goldmont
* - Atom Silvermont
@@ -1873,15 +1920,21 @@ static void intel_set_cpu_max_freq(void)
* which all now get by default arch_max_freq = SCHED_CAPACITY_SCALE
*/

- static_branch_enable(&arch_scale_freq_key);
+ u64 ratio = 1, turbo_ratio = 1;

if (turbo_disabled() ||
- x86_match_cpu(has_skx_turbo_ratio_limits) ||
x86_match_cpu(has_knl_turbo_ratio_limits) ||
x86_match_cpu(has_glm_turbo_ratio_limits))
return;

- core_set_cpu_max_freq();
+ if (skx_set_cpu_max_freq(&ratio, &turbo_ratio))
+ goto set_value;
+
+ core_set_cpu_max_freq(&ratio, &turbo_ratio);
+
+set_value:
+ arch_max_freq = div_u64(turbo_ratio * SCHED_CAPACITY_SCALE, ratio);
+ static_branch_enable(&arch_scale_freq_key);
}

static void init_scale_freq(void *arg)
--
2.16.4