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

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Date:	Sun, 15 Jul 2012 07:00:19 -0600
From:	David Ahern <dsahern@...il.com>
To:	Avi Kivity <avi@...hat.com>, Gleb Natapov <gleb@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf with precise attribute kills all KVM based VMs

On 7/15/12 2:07 AM, Avi Kivity wrote:
> On 07/12/2012 07:06 PM, Gleb Natapov wrote:
>>>
>>> Note the :pH this time.
>> I am not sure what perf kvm does with :pH modifier, but H modifier does
>> not make sense with perf kvm and should be reported as an error by perf tool.
>
> Maybe it should refer to the guest vs. the nested guest...

:H = host mode; you are thinking of :h for hypervisor mode. From 
perf-list documentation:

"Modifiers allow the user to restrict when events are
counted with 'u' for user-space, 'k' for kernel, 'h' for hypervisor.
Additional modifiers are 'G' for guest counting (in KVM guests) and 'H'
for host counting (not in KVM guests)."

>
> Well that's a horrible UI but we do need some way to distinguish among
> the two.  Samples from the nested guest's kernel will make no sense when
> looking at the guest kernel.  I guess we should default to exclude
> nested guest mode.
>

I catch a return flight in a couple of hours. I will send a summary 
email tonight to make sure we are on the same page with the problem, 
uses cases and patches.

David
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