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RE: [Xen-devel] Re: [RFC]PLE's performance enhancement through improving

To: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Re: [RFC]PLE's performance enhancement through improving scheduler.
From: "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
Date: Thu, 19 Aug 2010 09:57:24 +0800
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Thread-topic: [Xen-devel] Re: [RFC]PLE's performance enhancement through improving scheduler.
George Dunlap wrote:
> Xiantao,
> Thanks for the patch.  You have two changes here:
> * Yield goes back only 1 vcpu ("yield")
> * Other vcpus of yielding VM get yanked to the front ("boost")
> If you send them as two patches, we can talk about the changes /
> accept them individually.
> Both changes sound reasonable, but we often find in schedulers that
> small changes can have unexpected results. :-)
> I think the "yield" patch should be easy to accept.  The "boost" patch
> looks good but also seems riskier -- I'd want to do some more thinking
> and testing to make sure there aren't situations where it could cause
> problems, or allow one VM to "game" the scheduler to get more time.

Agree, we also thought this maybe a risk to unconditionally boost other vcpus' 
priority. We will investigate more before it is finally done. 
Basically, we thought the current scheduler is not fair for PLE-senstive 
guests, because it always yields its schedule chances to other vcpus in the 
runq once meet PLE vmexits, so only very little time is allocated for its run. 
Certainly, we also need to avoid malicous guests stealing time through the 
boost mechanism.  

> Would you mind running the vConsolidate test with each patch
> separately, so we can see how each one affects the performance?

Okay, we will perform the testing separately as you suggested.  

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