linux-kernel - Re: perf group read for inherited events

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Date:   Tue, 30 May 2017 06:57:14 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Vince Weaver <vince@...ter.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: perf group read for inherited events

On Tue, May 30, 2017 at 11:45:12AM +0200, Peter Zijlstra wrote:
> > Or is the simple patch below good enough?
> 
> The below seems to be the correct thing. It is rather unfortunate that
> this would break/significantly change existing semantics :/

The "existing semantics" as in ignoring the PERF_SAMPLE_READ in sample_type,
even though it wasn't implemented? It seems reasonable to me.

If you really worry about it could drop a printk_once in and see if it
triggers anywhere (and if yes drop the if completely)

The patch looks good to me. Please consider adding it.
I have some patches to use this in perf stat, will submit later.

-Andi