linux-kernel - Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side

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Date:	Thu, 15 Apr 2010 12:48:09 +0300
From:	Avi Kivity <avi@...hat.com>
To:	oerg Roedel <joro@...tes.org>
CC:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, zhiteng.huang@...el.com,
	tim.c.chen@...el.com, Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os	statistics
 from host side

On 04/15/2010 12:44 PM, oerg Roedel wrote:
>
>> So, we'd need something like the following:
>>
>>     if (exit == NMI)
>>         __get_cpu_var(nmi_vcpu) = vcpu;
>>
>>     stgi();
>>
>>     if (exit == NMI) {
>>         while (!nmi_handled())
>>             cpu_relax();
>>         __get_cpu_var(nmi_vcpu) = NULL;
>>     }
>>      
> Hmm, looks a bit complicated to me. The NMI should happen shortly after
> the stgi instruction. Interrupts are still disabled so we stay on this
> cpu. Can't we just set and erase the cpu_var at vcpu_load/vcpu_put time?
>
>    

That means an NMI that happens outside guest code (for example, in the 
mmu, or during the exit itself) would be counted as if in guest code.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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