linux-kernel - Re: [PATCH v1 5/5] KVM: Expose a version 1 architectural PMU to guests

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Message-ID: <1305722116.2466.7171.camel@twins>
Date:	Wed, 18 May 2011 14:35:16 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH v1 5/5] KVM: Expose a version 1 architectural PMU to
 guests

On Wed, 2011-05-18 at 14:37 +0300, Avi Kivity wrote:
> On 05/18/2011 02:32 PM, Peter Zijlstra wrote:
> > On Wed, 2011-05-18 at 13:07 +0200, Ingo Molnar wrote:
> > >
> > >  It does through raw events - which are indeed model specific.
> >
> > Which is exactly what is needed anyway, he gets a raw msr value.
> >
> > The only thing that is not exposed is the ANY bit, but since KVM doesn't
> > expose HT anyway that doesn't matter.
> 
> If I were to use raw events, I'd need to program AMD and Intel hosts 
> separately.  As it is, I just use the generic counters and the perf 
> backend does its thing.

But why exactly, from what I understood you emulate an actual hardware
PMU, that means the guest will be writing proper content to the relevant
MSRs, you can feed that directly into the raw config field (with
exception of the USR/OS/INT bits).

I'm fairly sure that emulating the intel arch bits on an cpu that
otherwise identifies itself as AMD is going to confuse things.


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