linux-kernel - Re: [RFC PATCHv3] perf tools: add event grouping capability to "perf stat"

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Date:	Thu, 25 Nov 2010 15:02:00 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Julia Lawall <julia@...u.dk>, Tom Zanussi <tzanussi@...il.com>,
	linux-kernel@...r.kernel.org, Matt Fleming <matt@...sole-pimps.org>
Subject: Re: [RFC PATCHv3] perf tools: add event grouping capability to
 "perf stat"

On Thu, 2010-11-25 at 14:19 +0100, Stephane Eranian wrote:

> I think using PERF_SAMPLE_READ may expose a problem in the
> perf.data format. To correctly parse a sample created with SAMPLE_READ,
> you need to know the attr.read_format. But for that you need to know the
> event which caused the sample, but for that you need the SAMPLE_ID,
> and you don't know if it's there or not. In other words, there is a chicken
> and egg problem.
> 
> I think the issue is that PERF_RECORD_SAMPLE is missing a mandatory
> piece of information: overflow event ID. This must a mandatory field, not
> optional as it is today. It is okay when you have only one group, but we'd
> like to go beyond that.



I'm not sure I get it, there's both PERF_FORMAT_ID and PERF_SAMPLE_ID,
so afaict there's a working combination for what you want to do.


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