Re: [PATCH V5 11/16] perf, core: Pass perf_sample_data to perf_callchain()

From: Peter Zijlstra
Date: Wed Sep 24 2014 - 10:15:20 EST

On Wed, Sep 10, 2014 at 10:09:08AM -0400, kan.liang@xxxxxxxxx wrote:
> From: Kan Liang <kan.liang@xxxxxxxxx>
> 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
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