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 18:14:19 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Avi Kivity <avi@...hat.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 Wednesday 14 April 2010 17:57:50 Avi Kivity wrote:
> 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.
> 
Callback seems too heavy, may affect the performance badly. Maybe a short 
queue would help, though this one is more complex.

But I am still curious if we extend the region, how much it would help. Would 
get a result soon...

-- 
regards
Yang, Sheng
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