From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: KVM PMU virtualization
Date: Fri, 26 Feb 2010 12:06:42 +0100
Message-ID: <20100226110642.GF4246@8bytes.org>
References: <4B86917C.4070102@redhat.com> <20100225173423.GB4246@8bytes.org> <20100226084241.GF15885@elte.hu> <4B87987A.2020302@redhat.com> <20100226103934.GD4246@8bytes.org> <20100226104659.GC7463@elte.hu>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Avi Kivity <avi@redhat.com>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	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>
Return-path: <kvm-owner@vger.kernel.org>
Received: from 8bytes.org ([88.198.83.132]:45134 "EHLO 8bytes.org"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S934028Ab0BZLGo (ORCPT <rfc822;kvm@vger.kernel.org>);
	Fri, 26 Feb 2010 06:06:44 -0500
Content-Disposition: inline
In-Reply-To: <20100226104659.GC7463@elte.hu>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Fri, Feb 26, 2010 at 11:46:59AM +0100, Ingo Molnar wrote:
> 
> * Joerg Roedel <joro@8bytes.org> wrote:
> 
> > On Fri, Feb 26, 2010 at 11:46:34AM +0200, Avi Kivity wrote:
> > > On 02/26/2010 10:42 AM, Ingo Molnar wrote:
> > >> Note that the 'soft PMU' still sucks from a design POV as there's no generic
> > >> hw interface to the PMU. So there would have to be a 'soft AMD' and a 'soft
> > >> Intel' PMU driver at minimum.
> > >>    
> > >
> > > Right, this will severely limit migration domains to hosts of the same  
> > > vendor and processor generation.  There is a  middle ground, though,  
> > > Intel has recently moved to define an "architectural pmu" which is not  
> > > model specific.  I don't know if AMD adopted it.  We could offer both  
> > > options - native host capabilities, with a loss of compatibility, and  
> > > the architectural pmu, with loss of model specific counters.
> > 
> > I only had a quick look yet on the architectural pmu from intel but it looks 
> > like it can be emulated for a guest on amd using existing features.
> 
> AMD CPUs dont have enough events for that, they cannot do the 3 fixed events 
> in addition to the 2 generic ones.

Good point. Maybe we can emulate that with some counter round-robin
usage if the guest really uses all 5 counters.

> Nor do you really want to standardize on KVM guests on returning 
> 'GenuineIntel' in CPUID, so that the various guest side OSs use the Intel PMU 
> drivers, right?

Isn't there a cpuid bit indicating the availability of architectural
perfmon?

	Joerg