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

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Date:	Tue, 13 Oct 2009 15:37:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	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


* 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.

	Ingo
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