From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jes Sorensen <Jes.Sorensen@redhat.com>
Subject: Re: KVM PMU virtualization
Date: Fri, 26 Feb 2010 14:34:43 +0100
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References: <20100226084241.GF15885@elte.hu> <4B87987A.2020302@redhat.com> <20100226104437.GB7463@elte.hu> <4B87AF44.9090702@redhat.com> <20100226114217.GI7463@elte.hu> <4B87B5DE.30503@redhat.com> <20100226120750.GA11578@elte.hu> <4B87BC74.7050207@redhat.com> <20100226123850.GA19476@elte.hu> <4B87C6C4.3040407@redhat.com> <20100226131841.GC2518@elte.hu>
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Cc: Avi Kivity <avi@redhat.com>, Joerg Roedel <joro@8bytes.org>,
	KVM General <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Zachary Amsden <zamsden@redhat.com>,
	Gleb Natapov <gleb@redhat.com>, ming.m.lin@intel.com,
	"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Arjan van de Ven <arjan@infradead.org>,
	Fr??d??ric Weisbecker <fweisbec@gmail.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
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On 02/26/10 14:18, Ingo Molnar wrote:
>
> * Avi Kivity<avi@redhat.com>  wrote:
>
>> Can you emulate the Core 2 pmu on, say, a P4? [...]
>
> How about the Pentium? Or the i486?
>
> As long as there's perf events support, the CPU can be supported in a soft
> PMU. You can even cross-map exotic hw events if need to be - but most of the
> tooling (in just about any OS) uses just a handful of core events ...

This is only possible if all future CPU perfmon events are guaranteed
to be a superset of previous versions. Otherwise you end up emulating
events and providing randomly generated numbers back.

The perfmon revision and size we present to a guest has to match the
current host.

Jes