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

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Date:	Mon, 7 Dec 2009 20:57:48 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.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

On Mon, Dec 07, 2009 at 08:48:05PM +0100, Frederic Weisbecker wrote:
> On Mon, Dec 07, 2009 at 04:38:03PM +0800, Xiao Guangrong wrote:
> > 
> > 
> > Ingo Molnar wrote:
> > 
> > > Also, i agree that the performance aspect is probably the most pressing 
> > > issue. Note that 'perf bench sched messaging' is very locking intense so 
> > > a 10x slowdown is not entirely unexpected - we still ought to optimize 
> > > it all some more. 'perf lock' is an excellent testcase for this in any 
> > > case.
> > > 
> > 
> > Here are some test results to show the overhead of lockdep trace events:
> > 
> >                    select    pagefault   mmap    Memory par   Cont_SW
> >                    latency    latency   latency   R/W BD      latency
> > 
> > disable ftrace        0         0         0         0          0
> > 
> > enable all ftrace  -16.65%    -109.80%   -93.62%   0.14%      -6.94%
> > 
> > enable all ftrace  -2.67%      1.08%     -3.65%   -0.52%      -0.68%
> > except lockdep
> > 
> > 
> > We also found big overhead when using kernbench and fio, but we haven't
> > verified whether it's caused by lockdep events.
> > 
> > Thanks,
> > Xiao
> 
> 
> This profile has been done using ftrace with perf right?
> It might be because the lock events are high rate events and
> fill a lot of perf buffer space. More than other events.
> 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.



I'm not sure who sent this email actually. May be you or Hitoshi.

But, anyway you got the point :)

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