linux-kernel - Re: [RFC PATCH 0/6] perf: Add AUX data sampling

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Date:   Fri, 23 Sep 2016 13:49:17 +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,
        vince@...ter.net, eranian@...gle.com,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        tglx@...utronix.de, ak@...ux.intel.com
Subject: Re: [RFC PATCH 0/6] perf: Add AUX data sampling

On Fri, Sep 23, 2016 at 02:27:20PM +0300, Alexander Shishkin wrote:
> Hi Peter,
> 
> This is an RFC, I'm not sending the tooling bits in this series,
> although they can be found here [1].
> 
> This series introduces AUX data sampling for perf events, which in
> case of our instruction/branch tracing PMUs like Intel PT, BTS, CS
> ETM means execution flow history leading up to a perf event's
> overflow.

This fails to explain _WHY_ this is a good thing to have. What kind of
analysis does this enable, and is that fully implemented in [1] (I
didn't look).

Please provide a bit more justification.