linux-kernel - Re: [RFC][PATCH] perf tools: Merge trace.info content into perf.data

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Date:	Wed, 7 Oct 2009 08:43:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Mike Galbraith <efault@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] perf tools: Merge trace.info content into
	perf.data


* Ingo Molnar <mingo@...e.hu> wrote:

> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > Hi,
> > 
> > Here is an attempt to remove the trace.info file. It works well for 
> > me, the reason for it to be an RFC is that I have doubts about the 
> > backward compatibility.
> > 
> > A file created by perf after his patch is unsupported by previous 
> > version because the size of the headers have increased.
> 
> That's OK i think in terms of trace.info - trace.info was a temporary 
> hack to begin with.
> 
> > That said, it's two new fields that have been added in the end of the 
> > headers, and those could be ignored by previous versions if they just 
> > handled the dynamic header size and then ignore the unknow part. The 
> > offsets guarantee the compatibility.
> 
> Yes, that's how it should work.
> 
> > But previous versions handle the header size using its static size, 
> > not dynamic, then it's not backward compatible.
> > 
> > Anyway, I'm not sure exactly how to handle that.
> 
> That's a bug in the previous version - mind doing a standalone fix for 
> that so we can mark it Cc: stable?

Meanwhile i've applied your two patches - they are clear steps forward. 
We'll need the -stable fix so that the new perf.data can be read. (and 
even that only affects -R afaics - so normal perf record / perf report 
is compatible.)

Btw., we also need a patch for new perf to read older perf.data files 
[non-trace.info ones], as those are not working either:

 $ perf report
   Fatal: incompatible file format

( We dont want to push it - i.e. i dont think we need to support old
  perf.data + trace.info combos. )

	Ingo
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