linux-kernel - Re: [UPDATED][PATCH][mmotm] Help Root Memory Cgroup Resource Counters Scale Better (v5)

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Date:	Thu, 13 Aug 2009 14:13:16 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"menage@...gle.com" <menage@...gle.com>, xemul@...nvz.org,
	prarit@...hat.com, andi.kleen@...el.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [UPDATED][PATCH][mmotm] Help Root Memory Cgroup Resource
	Counters Scale Better (v5)

* Ingo Molnar <mingo@...e.hu> [2009-08-13 10:35:24]:

> 
> * Balbir Singh <balbir@...ux.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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