linux-kernel - Re: [RFC] BTS based perf user callchains

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Date:	Mon, 02 Aug 2010 21:47:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Markus Metzger <markus.t.metzger@...el.com>,
	Robert Richter <robert.richter@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] BTS based perf user callchains

On Mon, 2010-08-02 at 20:41 +0200, Frederic Weisbecker wrote:
> On Mon, Aug 02, 2010 at 08:38:52PM +0200, Peter Zijlstra wrote:
> > On Mon, 2010-08-02 at 20:35 +0200, Frederic Weisbecker wrote:
> > > I'm not even sure that will work. Also, while looking at the BTS implementation
> > > in perf, I see we have one BTS buffer per cpu. But that doesn't look right as
> > > the code flow is not linear per cpu but per task. Hence I suspect we need
> > > one BTS buffer per task. But may be someone tried that and encountered a
> > > problem? 
> > 
> > IIRC we flush the buffer when we deschedule the counter.
> 
> 
> Ok. So the buffer is cut on schedule time. It might be nice
> to maintain the buffer progress across scheduling.

We flush it into the perf data buffer.
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