linux-kernel - Re: [PATCH v4 19/22] perf: Add infrastructure for using AUX data in perf samples

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Date:	Tue, 9 Sep 2014 11:11:38 +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
Subject: Re: [PATCH v4 19/22] perf: Add infrastructure for using AUX data in
 perf samples

On Wed, Aug 20, 2014 at 03:36:16PM +0300, Alexander Shishkin wrote:
> AUX data can be used to annotate other perf events by including it in
> sample records when PERF_SAMPLE_AUX flag is set. In this case, a kernel
> counter is created for each such event and trace data is retrieved
> from it and stored in the perf data stream.
> 
> To this end, new attribute fields are added:
>   * aux_sample_type: specify PMU on which the AUX data generating event
>                      is created;
>   * aux_sample_config: event config (maps to attribute's config field),
>   * aux_sample_size: size of the sample to be written.
> 
> This kernel counter is configured similarly to its "main" event with
> regards to filtering (exclude_{hv,idle,user,kernel}) and enabled state
> (disabled, enable_on_exec) to make sure that we don't get out of context
> AUX traces.

WHY? Why would we want to do this? This doesn't tell me why I should
want this or even consider it.

Convince me I want to read the patch.

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