Re: [patch 00/16] CFS Bandwidth Control v7

[Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>]

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(2011/06/23 21:43), Ingo Molnar wrote:
> 
> * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> 
>> On Wed, 2011-06-22 at 19:05 +0900, Hidetoshi Seto wrote:
>>
>>> I'll continue my test/benchmark on this v7 for a while. Though I 
>>> believe no more bug is there, I'll let you know if there is 
>>> something.
>>
>> Would that testing include performance of a kernel without these 
>> patches vs one with these patches in a configuration where the new 
>> feature is compiled in but not used?
>>
>> It does add a number of if (!cfs_rq->runtime_enabled) return 
>> branches all over the place, some possibly inside a function call 
>> (depending on what the auto-inliner does). So while the impact 
>> should be minimal, it would be very good to test it is indeed so.
> 
> Yeah, doing such performance tests is absolutely required. Branches 
> and instructions impact should be measured as well, beyond the cycles 
> impact.
> 
> The changelog of this recent commit:
> 
>   c8b281161dfa: sched: Increase SCHED_LOAD_SCALE resolution
> 
> gives an example of how to do such measurements.

Thank you for useful guidance!

I've run pipe-test-100k on both of a kernel without patches (3.0-rc4)
and one with patches (3.0-rc4+), in similar way as that described in
the change log you pointed (but I add "-d" for more details).

I sampled 4 results for each: repeat 10 times * 3 + repeat 200 times * 1.
Cgroups are not used in both, therefore of course CFS bandwidth control
is not used in one that have patched.  Results are archived and attached.

Here is a comparison in diff style:

=====
--- /home/seto/bwc-pipe-test/bwc-rc4-orig.txt   2011-06-24 11:52:16.000000000 +0900
+++ /home/seto/bwc-pipe-test/bwc-rc4-patched.txt        2011-06-24 12:08:32.000000000 +0900
 [seto@SIRIUS-F14 perf]$ taskset 1 ./perf stat -d -d -d --repeat 200 ../../../pipe-test-100k

  Performance counter stats for '../../../pipe-test-100k' (200 runs):

-        865.139070 task-clock                #    0.468 CPUs utilized            ( +-  0.22% )
-           200,167 context-switches          #    0.231 M/sec                    ( +-  0.00% )
-                 0 CPU-migrations            #    0.000 M/sec                    ( +- 49.62% )
-               142 page-faults               #    0.000 M/sec                    ( +-  0.07% )
-     1,671,107,623 cycles                    #    1.932 GHz                      ( +-  0.16% ) [28.23%]
-       838,554,329 stalled-cycles-frontend   #   50.18% frontend cycles idle     ( +-  0.27% ) [28.21%]
-       453,526,560 stalled-cycles-backend    #   27.14% backend  cycles idle     ( +-  0.43% ) [28.33%]
-     1,434,140,915 instructions              #    0.86  insns per cycle
-                                             #    0.58  stalled cycles per insn  ( +-  0.06% ) [34.01%]
-       279,485,621 branches                  #  323.053 M/sec                    ( +-  0.06% ) [33.98%]
-         6,653,998 branch-misses             #    2.38% of all branches          ( +-  0.16% ) [33.93%]
-       495,463,378 L1-dcache-loads           #  572.698 M/sec                    ( +-  0.05% ) [28.12%]
-        27,903,270 L1-dcache-load-misses     #    5.63% of all L1-dcache hits    ( +-  0.28% ) [27.84%]
-           885,210 LLC-loads                 #    1.023 M/sec                    ( +-  3.21% ) [21.80%]
-             9,479 LLC-load-misses           #    1.07% of all LL-cache hits     ( +-  0.63% ) [ 5.61%]
-       830,096,007 L1-icache-loads           #  959.494 M/sec                    ( +-  0.08% ) [11.18%]
-       123,728,370 L1-icache-load-misses     #   14.91% of all L1-icache hits    ( +-  0.06% ) [16.78%]
-       504,932,490 dTLB-loads                #  583.643 M/sec                    ( +-  0.06% ) [22.30%]
-         2,056,069 dTLB-load-misses          #    0.41% of all dTLB cache hits   ( +-  2.23% ) [22.20%]
-     1,579,410,083 iTLB-loads                # 1825.614 M/sec                    ( +-  0.06% ) [22.30%]
-           394,739 iTLB-load-misses          #    0.02% of all iTLB cache hits   ( +-  0.03% ) [22.27%]
-         2,286,363 L1-dcache-prefetches      #    2.643 M/sec                    ( +-  0.72% ) [22.40%]
-           776,096 L1-dcache-prefetch-misses #    0.897 M/sec                    ( +-  1.45% ) [22.54%]
+        859.259725 task-clock                #    0.472 CPUs utilized            ( +-  0.24% )
+           200,165 context-switches          #    0.233 M/sec                    ( +-  0.00% )
+                 0 CPU-migrations            #    0.000 M/sec                    ( +-100.00% )
+               142 page-faults               #    0.000 M/sec                    ( +-  0.06% )
+     1,659,371,974 cycles                    #    1.931 GHz                      ( +-  0.18% ) [28.23%]
+       829,806,955 stalled-cycles-frontend   #   50.01% frontend cycles idle     ( +-  0.32% ) [28.32%]
+       490,316,435 stalled-cycles-backend    #   29.55% backend  cycles idle     ( +-  0.46% ) [28.34%]
+     1,445,166,061 instructions              #    0.87  insns per cycle
+                                             #    0.57  stalled cycles per insn  ( +-  0.06% ) [34.01%]
+       282,370,988 branches                  #  328.621 M/sec                    ( +-  0.06% ) [33.93%]
+         5,056,568 branch-misses             #    1.79% of all branches          ( +-  0.19% ) [33.94%]
+       500,660,789 L1-dcache-loads           #  582.665 M/sec                    ( +-  0.06% ) [28.05%]
+        26,802,313 L1-dcache-load-misses     #    5.35% of all L1-dcache hits    ( +-  0.26% ) [27.83%]
+           872,571 LLC-loads                 #    1.015 M/sec                    ( +-  3.73% ) [21.82%]
+             9,050 LLC-load-misses           #    1.04% of all LL-cache hits     ( +-  0.55% ) [ 5.70%]
+       794,396,111 L1-icache-loads           #  924.512 M/sec                    ( +-  0.06% ) [11.30%]
+       130,179,414 L1-icache-load-misses     #   16.39% of all L1-icache hits    ( +-  0.09% ) [16.85%]
+       511,119,889 dTLB-loads                #  594.837 M/sec                    ( +-  0.06% ) [22.37%]
+         2,452,378 dTLB-load-misses          #    0.48% of all dTLB cache hits   ( +-  2.31% ) [22.14%]
+     1,597,897,243 iTLB-loads                # 1859.621 M/sec                    ( +-  0.06% ) [22.17%]
+           394,366 iTLB-load-misses          #    0.02% of all iTLB cache hits   ( +-  0.03% ) [22.24%]
+         1,897,401 L1-dcache-prefetches      #    2.208 M/sec                    ( +-  0.64% ) [22.38%]
+           879,391 L1-dcache-prefetch-misses #    1.023 M/sec                    ( +-  0.90% ) [22.54%]

-       1.847093132 seconds time elapsed                                          ( +-  0.19% )
+       1.822131534 seconds time elapsed                                          ( +-  0.21% )
=====

As Peter have expected, the number of branches is slightly increased.

-       279,485,621 branches                  #  323.053 M/sec                    ( +-  0.06% ) [33.98%]
+       282,370,988 branches                  #  328.621 M/sec                    ( +-  0.06% ) [33.93%]

However, looking overall, I think there is no significant problem on
the score with this patch set.  I'd love to hear from maintainers.


Thanks,
H.Seto

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