linux-kernel - Re: [PATCH V5 11/16] perf, core: Pass perf_sample_data to perf

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Message-ID: <20140924141507.GF2805@worktop.programming.kicks-ass.net>
Date:	Wed, 24 Sep 2014 16:15:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	kan.liang@...el.com
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
	paulus@...ba.org, acme@...nel.org, ak@...ux.intel.com,
	"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: Re: [PATCH V5 11/16] perf, core: Pass perf_sample_data to
 perf_callchain()

On Wed, Sep 10, 2014 at 10:09:08AM -0400, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> Haswell has a new feature that utilizes the existing Last Branch Record
> facility to record call chains. When the feature is enabled, function
> call will be collected as normal, but as return instructions are
> executed the last captured branch record is popped from the on-chip LBR
> registers.
> The LBR call stack facility can help perf to get call chains of progam
> without frame pointer.
> 
> This patch modifies various architectures' perf_callchain() to accept
> perf sample data. Later patch will add code that use the sample data to
> get call chains.

So I don't like this. Why not use the regular PERF_SAMPLE_BRANCH_STACK
output to generate the stuff from? We already have two different means,
with different transport, for callchains anyhow, so a third really won't
matter.
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