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

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Message-ID: <20170530170150.cx554x7nmbrzv7nc@hirez.programming.kicks-ass.net>
Date:   Tue, 30 May 2017 19:01:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
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 06:57:14AM -0700, Andi Kleen wrote:
> 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.

Right, so where we used to accept PERF_SAMPLE_READ on inherited events,
we now no longer will.

Note that it currently doesn't work right, even if it doesn't fail like
with the proposed patch.

Typically Vince will (rightly) complain when I change things like this.
But seeing how even if we accept it, it is fairly terminally buggered in
any case, we could change it.

Vince, do you know of anybody that would be immediately affected by
this?