linux-kernel - Re: [RFC PATCH 5/5] perf: Implement perf_output

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Date:	Wed, 19 May 2010 18:15:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	rostedt@...dmis.org
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/5] perf: Implement perf_output_addr()

On Wed, 2010-05-19 at 12:08 -0400, Steven Rostedt wrote:
> > Now suppose you have multiple active consumers of the tracepoint, either
> > you do the evaluation once and copy that around, or you do it multiple
> > times and end up with different results.
> 
> OK, this is where I'm getting a bit lost. The "multiple active
> consumers". Is this multiple instances of perf? Or perf doing multiple
> things with that event using different buffers? 

Multiple perf events of the same tracepoint, basically what you would en
up with if you were to allow multiple buffers.

Say task A and B both sample C's sched:sched_wakeup events. Then the
tracepoint will have two active perf_events hanging from it and we need
to fill two buffers.


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