linux-kernel - Re: [patch] perf_counter tools: remove expensive old debug code from perf top

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Date:	Tue, 13 Oct 2009 16:41:59 +0200
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch] perf_counter tools: remove expensive old debug code
 from perf top

On Tue, 2009-10-13 at 15:37 +0200, Ingo Molnar wrote:
> * Mike Galbraith <efault@....de> wrote:
> 
> > perf_counter tools: remove expensive old debug code from perf top
> > 
> > Calling gettimeofday() at high frequency is painful for handicapped 
> > boxen. The spot calling gettimeofday() is old unneeded debug code, so 
> > remove it.
> 
> Thanks!
> 
> We still seem to have a performance problem. Just running perf top on a 
> 16-way box:
> 
>  Performance counter stats for 'perf top -e cycles -c 3000000':
> 
>      585.694831  task-clock-msecs         #      0.113 CPUs 
>           35163  context-switches         #      0.060 M/sec
>              17  CPU-migrations           #      0.000 M/sec
>           20355  page-faults              #      0.035 M/sec
>      1476952962  cycles                   #   2521.711 M/sec
>       730770658  instructions             #      0.495 IPC  
>        11489471  cache-references         #     19.617 M/sec
>         2055001  cache-misses             #      3.509 M/sec
> 
>     5.169518576  seconds time elapsed
> 
> that's 11% of CPU time used on a single CPU - just displaying a measly 
> 16K irqs/sec. Something's not quite right here.

I'll try to figure out why after I do some more wakeup preempt testing.

btw, something broke top annotation (again).  Module symbols still
annotate, but vmlinux symbols went south.

	-Mike

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