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

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Message-ID: <4F3578FE.7030904@fb.com>
Date:	Fri, 10 Feb 2012 12:07:26 -0800
From:	Arun Sharma <asharma@...com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	<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 2/10/12 10:43 AM, Peter Zijlstra wrote:
> On Wed, 2012-01-25 at 11:50 -0800, Arun Sharma wrote:
>> # perf record -agP -e sched:sched_switch --filter "prev_state == 1 ||
>> prev_state == 2" -e  sched:sched_stat_sleep -- sleep 3
>
> Problem with that is it'll try and do a backtrace for all events, not
> only the sched_switch but also sched_stat_sleep, which is completely
> superfluous (and expensive).
>
> Currently perf tool doesn't support individual -g flags though and its
> slightly non-trivial to make it so. Easiest work-around would be two
> records and then merge the two files.

If we have a sequence of:

SL1, SW1, SL2, SW2, SL3, SW3

I think you're suggesting:

perf.data1: SL1, SL2, SL3 (without -g)
perf.data2: SW1, SW2, SW3 (with -g)

and then munge the data to create perf.data. But making sure that all 
matching sleep and switch events are captured seems hard.

  -Arun


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