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

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [RFC]PLE's performance enhancement through improving scheduler.
From: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Date: Wed, 18 Aug 2010 10:16:52 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
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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.

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


On Wed, Aug 18, 2010 at 7:39 AM, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
> On 18/08/2010 06:51, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:
>> The attached patch is just for RFC, not for check-in. Recently, we are 
>> working
>> on enhancing the hardware feature PLE through improving scheduler in Xen, and
>> the attached patch can improve system's throughput significantly. With
>> standand virtualization benchmark(vConsolidate), the testing result shows
>> ~20% performance gain.   In the implemenation, there are two points to 
>> enhance
>> the system's scheduler.
>> The first one is that when PLE vmexit occurs,  scheduler de-schedules the 
>> vcpu
>> and put it in the second position of the runq instead of moving it to the 
>> tail
>> of runq so that it can be re-scheduled in a very short time. In this case, it
>> can improve scheduler's faireness and make the PLE-senstive guests allocated
>> with reasonable timeslice.  The other improvement is to boost other vcpus'
>> priority of the same guest through moving them to the head of the runq when
>> PLE vmexit happens with one vcpu of the guest.  And we are also improving the
>> implementation to make it more robust and more pervasive, but before the work
>> is done, we also want to collect your guys' ideas and suggestions about it ?
>> Any comment is very appreciated!. Thanks!
>> Xiantao
> Please Cc George Dunlap on scheduler work.
>  -- Keir
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