linux-kernel - Re: [PATCH v2] perf/sched: fix for getting task's execution time

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Date:	Mon, 7 Dec 2009 08:30:43 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Xiao Guangrong <ericxiao.gr@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	T??r??k Edwin <edwintorok@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] perf/sched: fix for getting task's execution time


* Xiao Guangrong <xiaoguangrong@...fujitsu.com> wrote:

> In current code, task's execute time is got by reading
> '/proc/<pid>/sched' file, it's wrong if the task is created
> by pthread_create(), because every thread task has same pid.
> 
> This way also has two demerits:
> 
> 1: 'perf sched replay' can't work if the kernel not compile with
>    'CONFIG_SCHED_DEBUG' option
> 2: perf tool should depend on proc file system
> 
> So, this patch call getrusage() to get task's execution time instead
> of reading /proc file

ok, that's better than /proc, but how about using 
PERF_COUNT_SW_TASK_CLOCK instead of rusage, to recover the CPU time 
used? It would be more precise, and it would use the perf API. (Some 
helper functions in tools/perf/lib/ would be nice to make it as easy to 
use as rusage (or even easier if possible).)

	Ingo
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