From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics
 from host side
Date: Wed, 14 Apr 2010 13:19:49 +0300
Message-ID: <4BC596C5.7020507@redhat.com>
References: <1902387910.2078.435.camel@ymzhang.sh.intel.com> <201004141743.32393.sheng@linux.intel.com> <4BC5919E.1010400@redhat.com> <201004141814.19330.sheng@linux.intel.com>
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Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Marcelo Tosatti <mtosatti@redhat.com>,
	oerg Roedel <joro@8bytes.org>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	Gleb Natapov <gleb@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>, zhiteng.huang@intel.com,
	tim.c.chen@intel.com, Arnaldo Carvalho de Melo <acme@infradead.org>
To: Sheng Yang <sheng@linux.intel.com>
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On 04/14/2010 01:14 PM, Sheng Yang wrote:
>
>> 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.
>    

The patch we're replying to adds callbacks (to read rip, etc.), so it's 
no big deal.  For the queue solution, a queue of size one would probably 
be sufficient even if not guaranteed by the spec.  I don't see how the 
cpu can do another guest entry without delivering the NMI.

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

Yes, interesting to see what the latency is.  If it's reasonably short 
(and I expect it will be so), we can do the busy wait solution.

If we have an NMI counter somewhere, we can simply wait until it changes.

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