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

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Date:	Wed, 14 Apr 2010 12:57:50 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Sheng Yang <sheng@...ux.intel.com>
CC:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	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 04/14/2010 12:43 PM, Sheng Yang wrote:
> On Wednesday 14 April 2010 17:20:15 Avi Kivity wrote:
>    
>> On 04/14/2030 12:05 PM, Zhang, Yanmin wrote:
>>      
>>> Here is the new patch of V3 against tip/master of April 13th
>>> if anyone wants to try it.
>>>        
>> Thanks for persisting despite the flames.
>>
>> Can you please separate arch/x86/kvm part of the patch?  That will make
>> for easier reviewing, and will need to go through separate trees.
>>
>> Sheng, did you make any progress with the NMI injection issue?
>>      
> Yes, though some other works interrupt me lately...
>
> The very first version has issue due to SELF_IPI mode can't be used to send
> NMI according to SDM. That's the reason why x2apic don't have way to do this.
>    

Yes, I see that now.  Looks like others have the same questions...

> But later I found another issue of fail to inspect inside the guest. I think
> it's due to NMI is asynchronous event, though it should be triggered very
> quickly, you can't guarantee that the handler would be triggered before the
> state(current_vcpu) is cleared with current code.
>
> Maybe just extended the "guest state" region would be fine, if the latency is
> stable enough(though I think it maybe platform depended). I am working on this
> now.
>    

I wouldn't like to depend on model specific behaviour.

One option is to read all the information synchronously and store it in 
a per-cpu area with atomic instructions, then queue the NMI.  Another 
option is to have another callback which tells us that the NMI is done, 
and have a busy loop wait until the NMI is delivered.

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

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