linux-kernel - Re: [PATCH] perf_events: add PERF_SAMPLE_BRANCH

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Date:	Wed, 07 Apr 2010 15:15:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com, robert.richter@....com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com
Subject: Re: [PATCH] perf_events: add PERF_SAMPLE_BRANCH_STACK

On Wed, 2010-04-07 at 14:45 +0200, Stephane Eranian wrote:
>         LBR is configured by default to record ALL taken branches.  On some
>         processors, it is possible to filter the type of branches. This will
>         be supported in a subsequent patch.
> 
>         On other processors, the sample type is allowed but will generate a
>         sample where nr=0 as is the case with other sampling types.

Right, so I already posted a patch like that:
  http://lkml.org/lkml/2010/3/4/160

and the reason its not merged is because there is no perf use-case for
it. Ingo wants to avoid merging ABI bits for which there is no userspace
around. We already have a few such things and we find that its too easy
to regress on those part.

So if you want this, please also implement a useful use-case in perf.

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