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

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Message-ID: <5002BF9B.8090306@redhat.com>
Date:	Sun, 15 Jul 2012 16:03:23 +0300
From:	Avi Kivity <avi@...hat.com>
To:	David Ahern <dsahern@...il.com>
CC:	Gleb Natapov <gleb@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf with precise attribute kills all KVM based VMs

On 07/15/2012 04:00 PM, David Ahern wrote:
> 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)."

No, it's an additional distinction.  A kvm guest can be in kernel mode,
user mode, or in a nested guest mode (which has its own user mode and
kernel mode).  Currently we have no way of distinguishing between guest
kernel mode and nested guest kernel mode.

I assume 'h' means profiling the hypervisor from a guest (i.e. xen dom0)?

-- 
error compiling committee.c: too many arguments to function


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