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Date: Thu, 26 Jan 2012 03:21:31 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Arun Sharma <asharma@fb.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-kernel@vger.kernel.org,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Andrew Vagin <avagin@openvz.org>, Ingo Molnar <mingo@elte.hu>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] trace: reset sleep/block start time on task switch
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On Wed, Jan 25, 2012 at 11:50:53AM -0800, Arun Sharma wrote:
> On 1/25/12 1:20 AM, Frederic Weisbecker wrote:
> 
> >>>I'm tempted to revert 1ac9bc69 for now, userspace will simply have to
> >>>correlate trace_sched_switch() and trace_sched_stat_{sleep,blocked}(),
> >>>which shouldn't be too hard.
> >>
> >>We tried it and it didn't work very well. Especially when used with
> >>perf record -g. There are too many uninteresting
> >>trace_sched_switch() events.
> >
> >You mean context switches happening when the prev task doesn't need
> >to block or so? As it happens with preemption for example?
> >
> >In this case you can use filters to drop context switches for
> >which the prev state is not S or D.
> 
> We had these filters and still couldn't keep up:
> 
> # perf record -agP -e sched:sched_switch --filter "prev_state == 1
> || prev_state == 2" -e  sched:sched_stat_sleep -- sleep 3
> [ perf record: Woken up 107 times to write data ]
> [ perf record: Captured and wrote 32.629 MB perf.data (~1425585 samples) ]
> Warning:
> Processed 104066 events and lost 4 chunks!
> 
> Check IO/CPU overload!

Have you tried to tweak the -m options to increase the size of the buffer?

> 
>  -Arun