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

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Date:	Fri, 27 Feb 2015 15:57:02 -0800
From:	Andi Kleen <ak@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kan.liang@...el.com, linux-kernel@...r.kernel.org,
	mingo@...hat.com, acme@...nel.org
Subject: Re: [RFC PATCH 1/1] proc: introduce /proc/<pid>/lbr_stack

On Fri, Feb 27, 2015 at 11:05:45PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 27, 2015 at 09:54:34AM -0800, Andi Kleen wrote:
> > > > perf record doesn't show where you're currently blocked.
> > > 
> > > Of course it does; look at perf inject -s.
> > 
> > Trace points don't support the LBR stack.
> 
> Yes, indeed. But would it not make much more sense to squirrel the LBR
> state into sched:sched_switch and teach that inject -s thing to dtrt,
> than to make a proc file that's available on all archs but will only
> work on 1-2 x86 uarchs and only if you're also running the right magic
> perf record at the same time?

Yes. It would be nice to capture the whole PMU state in trace points.
There are use models for this where it can work better than
sampling.

But that would be a lot bigger project than this simple file,
which is already quite useful with minimal effort.

-Andi

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