linux-kernel - Re: [PATCH 2/2] perf lock: New subcommand "lock" to perf for analyzing lock statistics

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Date:	Tue, 08 Dec 2009 09:31:26 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Steven Rostedt <srostedt@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH 2/2] perf lock: New subcommand "lock" to perf for	analyzing
 lock statistics

Hi Frederic,

Frederic Weisbecker wrote:

> This profile has been done using ftrace with perf right?

We not use perf, just operate it by debugfs, the test procedure
is like below:

case 1: disable all trace events:
echo nop > debugfs/tracing/current_tracer
echo > debugfs/tracing/set_event
run benchmarks
...

case 2: enable all trace events except lockdep:
echo nop > debugfs/tracing/current_tracer
echo *:* > debugfs/tracing/set_event
echo 0 >  debugfs/tracing/events/lockdep/enable
run benchmarks
...

> In one of your previous mails, you showed us the difference
> of the size of perf.data by capturing either scheduler events
> or lock events.
> 

It's not my work :-)

Thanks,
Xiao

> And IIRC, the case of lock events resulted in a 100 MB perf.data
> whereas it was a small file for sched events.
> 
> The overhead in the pagefault and mmap latency could then
> result in the fact we have much more events to save, walking
> through much more pages in perf buffer, then faulting more often,
> etc.
> 
> Plus the fact various locks are taken in mmap and fault path,
> generating more lock events.
> 
> Just a guess...
> 
> 
> 

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