Re: [RFC PATCH 1/1] proc: introduce /proc/<pid>/lbr_stack

From: Peter Zijlstra
Date: Mon Feb 23 2015 - 11:50:12 EST

On Mon, Feb 23, 2015 at 03:43:41AM +0000, 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. It has been implemented in perf. The
> call chains information is saved during perf event context.
> This patch exposes a /proc/<pid>/lbr_stack file that shows the saved LBR
> call chain information.

But why? I mean, this thing is only useful if you have a concurrently
running perf record that selects the LBR-stack stuff.

And if you have that, you might as well look at its output instead. Why
add this unconditional proc file that doesn't function on its own?
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