linux-kernel - Re: [PATCH][KVM][retry 4] Add support for Pause Filtering to AMD SVM

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Message-ID: <4A15151A.6000708@redhat.com>
Date:	Thu, 21 May 2009 11:47:22 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Mark Langsdorf <mark.langsdorf@....com>
CC:	Joerg Roedel <joerg.roedel@....com>, peterz@...radead.org,
	Ingo Molnar <mingo@...e.hu>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][KVM][retry 4] Add support for Pause Filtering to AMD
 SVM

Mark Langsdorf wrote:
> This feature creates a new field in the VMCB called Pause
> Filter Count.  If Pause Filter Count is greater than 0 and
> intercepting PAUSEs is enabled, the processor will increment
> an internal counter when a PAUSE instruction occurs instead
> of intercepting.  When the internal counter reaches the
> Pause Filter Count value, a PAUSE intercept will occur.
>
> This feature can be used to detect contended spinlocks,
> especially when the lock holding VCPU is not scheduled.
> Rescheduling another VCPU prevents the VCPU seeking the
> lock from wasting its quantum by spinning idly.  Perform
> the reschedule by increasing the the credited time on
> the VCPU.
>
> Experimental results show that most spinlocks are held
> for less than 1000 PAUSE cycles or more than a few
> thousand.  Default the Pause Filter Counter to 3000 to
> detect the contended spinlocks.
>
> Processor support for this feature is indicated by a CPUID
> bit.
>
> On a 24 core system running 4 guests each with 16 VCPUs,
> this patch improved overall performance of each guest's
> 32 job kernbench by approximately 1%.  Further performance
> improvement may be possible with a more sophisticated
> yield algorithm.
>   

Please split this into a scheduler patch and a kvm patch.


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

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