linux-kernel - Re: [PATCH v5 06/20] perf: Add AUX record

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Message-ID: <20141022150715.GF21513@worktop.programming.kicks-ass.net>
Date:	Wed, 22 Oct 2014 17:07:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, acme@...radead.org,
	mathieu.poirier@...aro.org
Subject: Re: [PATCH v5 06/20] perf: Add AUX record

On Wed, Oct 22, 2014 at 05:18:29PM +0300, Alexander Shishkin wrote:
> Peter Zijlstra <peterz@...radead.org> writes:
> 
> > On Mon, Oct 13, 2014 at 04:45:34PM +0300, Alexander Shishkin wrote:
> >> +	/*
> >> +	 * Records that new data landed in the AUX buffer part.
> >> +	 *
> >> +	 * struct {
> >> +	 * 	struct perf_event_header	header;
> >> +	 *
> >> +	 * 	u64				aux_offset;
> >> +	 * 	u64				aux_size;
> >> +	 *	u64				flags;
> >> +	 * 	struct sample_id		sample_id;
> >> +	 * };
> >> +	 */
> >> +	PERF_RECORD_AUX				= 11,
> >
> > Given the discussion with the ARM people the last time, do we want to
> > add the possibility of a variable data field in this event? Its easy to
> > add now, harder to do later (although not impossible).
> 
> Iirc, what they want is to save a once-per-session chunk of data, which
> would be better synthesized by perf record than sent from a pmu driver?
> 
> We do something like that with PT right now, perf record looks at pmu's
> sysfs attributes and stores them in some synthesized record.

Right, I just got to that. So I wasn't entirely sure if perf_event_open
time conditions where sufficient for them, if they are then yes that
could work.
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