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

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Message-ID: <4FFCBD00.1030109@gmail.com>
Date:	Tue, 10 Jul 2012 17:38:40 -0600
From:	David Ahern <dsahern@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Avi Kivity <avi@...hat.com>, Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf with precise attribute kills all KVM based VMs

On 7/9/12 8:59 AM, Peter Zijlstra wrote:
> 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.
>

Any updates on the options for this or is there still squinting going on 
with MSR orders?

I guess it's a good thing Ingo's request for :pp to be the default was 
not implemented:
   https://lkml.org/lkml/2012/5/14/26

David
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