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

[Peter Zijlstra]

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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