Messages in this thread | | | From | Nikhil Rao <> | Date | Tue, 26 Apr 2011 09:11:25 -0700 | Subject | Re: [RFC][PATCH 00/18] Increase resolution of load weights |
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On Wed, Apr 20, 2011 at 11:16 PM, Ingo Molnar <mingo@elte.hu> wrote: > > * Nikhil Rao <ncrao@google.com> wrote: > >> Major TODOs: >> - Detect overflow in update shares calculations (time * load), and set load_avg >> to maximum possible value (~0ULL). >> - tg->task_weight uses an atomic which needs to be updates to 64-bit on 32-bit >> machines. Might need to add a lock to protect this instead of atomic ops. >> - Check wake-affine math and effective load calculations for overflows. >> - Needs more testing and need to ensure fairness/balancing is not broken. > > Please measure micro-costs accurately as well, via perf stat --repeat 10 or so. > > For example, on a testsystem doing 200k pipe triggered context switches (100k > pipe ping-pongs) costs this much: > > $ taskset 1 perf stat --repeat 10 ./pipe-test-100k > > 630.908390 task-clock-msecs # 0.434 CPUs ( +- 0.499% ) > 200,001 context-switches # 0.317 M/sec ( +- 0.000% ) > 0 CPU-migrations # 0.000 M/sec ( +- 66.667% ) > 145 page-faults # 0.000 M/sec ( +- 0.253% ) > 1,374,978,900 cycles # 2179.364 M/sec ( +- 0.516% ) > 1,373,646,429 instructions # 0.999 IPC ( +- 0.134% ) > 264,223,224 branches # 418.798 M/sec ( +- 0.134% ) > 16,613,988 branch-misses # 6.288 % ( +- 0.755% ) > 204,162 cache-references # 0.324 M/sec ( +- 18.805% ) > 5,152 cache-misses # 0.008 M/sec ( +- 21.280% ) > > We want to know the delta in the 'instructions' value resulting from the patch > (this can be measured very accurately) and we also want to see the 'cycles' > effect - both can be measured pretty accurately. > > I've attached the testcase - you might need to increase the --repeat value so > that noise drops below the level of the effect from these patches. (the effect > is likely in the 0.01% range) >
Thanks for the test program. Sorry for the delay in getting back to you with results. I had some trouble wrangling machines :-(
I have data from pipe_test_100k on 32-bit builds below. I ran this test 5000 times on each kernel with the two events (instructions, cycles) configured (the test machine does not have enough PMUs to measure all events without scaling).
taskset 1 perf stat --repeat 5000 -e instructions,cycles ./pipe-test-100k
baseline (v2.6.39-rc4):
Performance counter stats for './pipe-test-100k' (5000 runs):
994,061,050 instructions # 0.412 IPC ( +- 0.133% ) 2,414,463,154 cycles ( +- 0.056% )
2.251820874 seconds time elapsed ( +- 0.429% )
kernel + patch:
Performance counter stats for './pipe-test-100k' (5000 runs):
1,064,610,666 instructions # 0.435 IPC ( +- 0.086% ) 2,448,568,573 cycles ( +- 0.037% )
1.704553841 seconds time elapsed ( +- 0.288% )
We see a ~7.1% increase in instructions executed and a 1.4% increase in cycles. We also see a 5.5% increase in IPC (understandable since we do more work). I can't explain how elapsed time drops by about 0.5s though.
> It would also be nice to see how 'size vmlinux' changes with these patches > applied, on a 'make defconfig' build. >
With a defconfig build, we see a marginal increase in vmlinux text size (3049 bytes, 0.043%), and a small decreased in data size (-4040 bytes, -0.57%).
baseline (v2.6.39-rc4): text data bss dec hex filename 7025688 711604 1875968 9613260 92afcc vmlinux-2.6.39-rc4
kernel + patch: text data bss dec hex filename 7028737 707564 1875968 9612269 92abed vmlinux
-Thanks Nikhil
> Thanks, > > Ingo > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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