linux-kernel - Re: [PATCH 01/17] perf util: Save pid-cmdline mapping into tracing header

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Date:	Wed, 31 Jul 2013 09:51:54 +0900
From:	Namhyung Kim <namhyung.kim@....com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Jeremy Eder <jeder@...hat.com>
Subject: Re: [PATCH 01/17] perf util: Save pid-cmdline mapping into tracing
 header

Hi Arnaldo,

2013-07-30 오후 10:28, Arnaldo Carvalho de Melo 쓴 글:
> Em Tue, Jul 30, 2013 at 06:18:58PM +0900, Namhyung Kim escreveu:
>> From: Namhyung Kim <namhyung.kim@....com>
>>
>> Current trace info data lacks the saved cmdline mapping which is
>> needed for pevent to find out the comm of a task.  Add this and bump
>> up the version number so that perf can determine its presence when
>> reading.
>
> Can't we get this from the PERF_RECORD_COMM synthesized at the beginning
> of the session + the kernel generated ones for new threads?
>
> We would just call machine__find_thread() and use thread->comm, etc, no?

Yes, I think it's doable.  However it needs an additional perf event 
only to generate the COMM events.  So I decided not to do it and reused 
saved cmdline info from ftrace.  But IIUC it also has a problem of 
possible information loss due to the size of table.

Thanks,
Namhyung

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