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Date: Thu, 27 Feb 2014 12:51:43 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Will Deacon <Will.Deacon@arm.com>, Dave P Martin <Dave.Martin@arm.com>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH 7/7] perf: kill perf_event_context::pmu
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On Thu, Feb 27, 2014 at 11:48:05AM +0000, Mark Rutland wrote:
> On Tue, Feb 25, 2014 at 11:31:00AM +0000, Peter Zijlstra wrote:
> > On Tue, Feb 11, 2014 at 05:56:51PM +0000, Mark Rutland wrote:
> > > Another option would be to have a context per-pmu. Each context's pmu
> > > pointer would be valid, and (other than the case of software events) it
> > > doesn't make sense to place events from disparate PMUs into the same
> > > group anyway. Then you don't need a fixed sized pmu list in the context
> > > or some arcane list structs.
> > 
> > No it does make sense; for example on hardware that doesn't have a PMI
> > you can create a software event + hardware event group and have the
> > software interrupt read the hardware counter and still get 'some'
> > sampling.
> 
> Sure, I called out software events as an exception above.

Oh sorry missed that.

> Does it ever make sense to group two hardware events for disparate
> hardware PMUs?

No, and I think we disallow that. We only explicitly allow software
events/groups to move to !software context.