linux-kernel - Re: [PATCH V2 1/6] perf,core: allow invalid context events to be part of sw/hw groups

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Date:	Thu, 16 Apr 2015 23:23:42 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Kan Liang <kan.liang@...el.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/6] perf,core: allow invalid context events to be
 part of sw/hw groups

> From my PoV that makes sense. One is CPU-affine, the other is not, and
> the two cannot be scheduled in the same PMU transaction by the nature of
> the hardware. Fundamentally, you cannot provide group semantics due to
> this.

Actually you can. Just use it like a free running counter, and the
different groups sample it. This will work from the different CPUs,
as long as the event is the same everywhere.

The implemention may not be quite right yet, but the basic concept 
should work, and is useful.

-Andi
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