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

[Andi Kleen]

On Mon, Feb 23, 2015 at 05:49:57PM +0100, Peter Zijlstra wrote:
> 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?

perf record doesn't show where you're currently blocked.

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only
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