linux-kernel - Re: [RFC PATCH 1/1] proc: introduce /proc/<pid>/lbr

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Message-ID: <20150223164957.GB5029@twins.programming.kicks-ass.net>
Date:	Mon, 23 Feb 2015 17:49:57 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	kan.liang@...el.com
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, acme@...nel.org,
	ak@...ux.intel.com
Subject: Re: [RFC PATCH 1/1] proc: introduce /proc/<pid>/lbr_stack

On Mon, Feb 23, 2015 at 03:43:41AM +0000, 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. 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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