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SubjectRe: [UPDATED][PATCH][mmotm] Help Root Memory Cgroup Resource Counters Scale Better (v5)
* Ingo Molnar <mingo@elte.hu> [2009-08-13 10:35:24]:

>
> * Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>
> > Without Patch
> >
> > Performance counter stats for '/home/balbir/parallel_pagefault':
> >
> > 5826093739340 cycles # 809.989 M/sec
> > 408883496292 instructions # 0.070 IPC
> > 7057079452 cache-references # 0.981 M/sec
> > 3036086243 cache-misses # 0.422 M/sec
>
> > With this patch applied
> >
> > Performance counter stats for '/home/balbir/parallel_pagefault':
> >
> > 5957054385619 cycles # 828.333 M/sec
> > 1058117350365 instructions # 0.178 IPC
> > 9161776218 cache-references # 1.274 M/sec
> > 1920494280 cache-misses # 0.267 M/sec
>
> Nice how the instruction count and the IPC value incraesed, and the
> cache-miss count decreased.
>
> Btw., a 'perf stat' suggestion: you can also make use of built-in
> error bars via repeating parallel_pagefault N times:
>
> aldebaran:~> perf stat --repeat 3 /bin/ls
>
> Performance counter stats for '/bin/ls' (3 runs):
>
> 1.108886 task-clock-msecs # 0.875 CPUs ( +- 4.316% )
> 0 context-switches # 0.000 M/sec ( +- 0.000% )
> 0 CPU-migrations # 0.000 M/sec ( +- 0.000% )
> 254 page-faults # 0.229 M/sec ( +- 0.000% )
> 3461896 cycles # 3121.958 M/sec ( +- 3.508% )
> 3044445 instructions # 0.879 IPC ( +- 0.134% )
> 21213 cache-references # 19.130 M/sec ( +- 1.612% )
> 2610 cache-misses # 2.354 M/sec ( +- 39.640% )
>
> 0.001267355 seconds time elapsed ( +- 4.762% )
>
> that way even small changes in metrics can be identified as positive
> effects of a patch, if the improvement is beyond the error
> percentage that perf reports.
>
> For example in the /bin/ls numbers i cited above, the 'instructions'
> value can be trusted up to 99.8% (with a ~0.13% noise), while say
> the cache-misses value can not really be trusted, as it has 40% of
> noise. (Increasing the repeat count will drive down the noise level
> - at the cost of longer measurement time.)
>
> For your patch the improvement is so drastic that this isnt needed -
> but the error estimations can be quite useful for more borderline
> improvements. (and they are also useful in finding and proving small
> performance regressions)

Thanks for the tip, let me try and use the repeats feature. BTW, nice
work on the perf counters, I was pleasantly surprised to see a
wonderful tool in the kernel with a good set of options and detailed
analysis capabilities.

--
Balbir


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