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Date: Mon, 23 Feb 2015 09:44:48 -0800
From: Andi Kleen <ak@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kan.liang@intel.com, linux-kernel@vger.kernel.org, mingo@redhat.com,
        acme@kernel.org
Subject: Re: [RFC PATCH 1/1] proc: introduce /proc/<pid>/lbr_stack
Message-ID: <20150223174448.GE27767@tassilo.jf.intel.com>
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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@intel.com wrote:
> > From: Kan Liang <kan.liang@intel.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?

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

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only
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