linux-kernel - Re: perf with precise attribute kills all KVM based VMs

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Date:	Mon, 09 Jul 2012 16:59:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	David Ahern <dsahern@...il.com>, Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf with precise attribute kills all KVM based VMs

On Mon, 2012-07-09 at 17:51 +0300, Avi Kivity wrote:
> On 07/09/2012 05:49 PM, Peter Zijlstra wrote:
> > On Mon, 2012-07-09 at 08:47 -0600, David Ahern wrote:
> >> 
> >> I found this testing changes to perf-kvm, but found the problem extends 
> >> to just perf-record. With perf-record exclude_guest defaults to 1. See 
> >> tools/perf/util/util.c, event_attr_init(). 
> > 
> > You lost me there.. so perf-record defaults to exclude_guest=1 (which
> > would make the proposed patch I just send actually possible), but its
> > still going *bang* ?
> 
> It's possible that the DS writes overshoot the MSR... or that there's a
> bug somewhere.

OK, so the first thing to stare at is in what order the MSRs are
touched, I think you first need to stop the counter, then clear the PEBS
bits, then clear the DS_AREA one.

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