linux-kernel - Re: [PATCH] trace: reset sleep/block start time on task switch

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Message-ID: <4F205D1D.1020304@fb.com>
Date:	Wed, 25 Jan 2012 11:50:53 -0800
From:	Arun Sharma <asharma@...com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	<linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Andrew Vagin <avagin@...nvz.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] trace: reset sleep/block start time on task switch

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!

  -Arun
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