linux-kernel - Re: [PATCH V2 12/15] perf tools: allow non-matching sample types

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Date:	Tue, 02 Jul 2013 10:09:58 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	David Ahern <dsahern@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V2 12/15] perf tools: allow non-matching sample types

On 01/07/13 21:53, David Ahern wrote:
> On 7/1/13 3:32 AM, Adrian Hunter wrote:
>> Snip
>>
>>>
>>> While this works for a combined S/W and tracepoint events session, I do not
>>> like promoting sample types to the minimum compatible level for all events
>>> in the session. perf needs to allow each event to have its own sample_type
>>> and not force a minimal compatibility.
>>
>> Why?  The impact is small. The kernel API is completely unchanged.
> 
> I'd like to see libperf become a stable, usable library - usable by more
> than the perf binary and its builtin commands. I have already done this once
> for a daemon, and it was a PITA to get the specific use functional without
> memory leaks/growth in the libperf part.
> 
> With respect to this specific patch it means appropriate flexibility in the
> data collected for events. ie., each event can have its own sample_type. For
> example if the tracepoint already contains task information TID is not
> needed - and IP may not be wanted either. The code processing the samples
> should not require all events to have some minimum data format - that just
> wastes buffer space.

It would be more compelling to provide a use-case where that "waste"
actually makes any difference.

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