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[Xen-devel] Re: CPU usage for credit2

To: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: CPU usage for credit2
From: Yuehai Xu <yuehaixu@xxxxxxxxx>
Date: Fri, 24 Sep 2010 10:14:36 -0400
Cc: xen-tools@xxxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, yhxu@xxxxxxxxx
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On Fri, Sep 24, 2010 at 7:38 AM, George Dunlap
<George.Dunlap@xxxxxxxxxxxxx> wrote:
> I assume that your system has more than 1 PCPU, and that you're using
> pinning to try to limit the VM to 1 PCPU?

Yes, you are correct. In order to test the performance of credit2 for
the problem of mix work load, I pin VCPUs from VMs to a PCPU while the
VCPU of Dom0 pins to another PCPU.

> At the moment, the credit2 scheduler doesn't implement pinning -- cpu
> affinity is entirely ignored.  (It is an experimental scheduler, after all.)
>  I think theoretically making pinning function shouldn't be too hard; but
> making the credit algorithm work with an arbitrary combination of affinities
> would require some careful thinking, and might not even be possible.

So, the result that I got, which shows almost 100% usage of CPU for
each VCPU, is actually because the VCPUs use different PCPUs instead
of a single one, is that correct?

> If you want, you can try to use cpu pools to isolate the two VMs to a single
> PCPU.  I haven't tried credit2 with pools yet, but in theory it should work.

Ok, I will try it and tell you the result once I get it.


>  -George
> On 23/09/10 14:48, Yuehai Xu wrote:
>> Hi,
>> Suppose 2 VMs both of which just has a single VCPU share a single
>> PCPU, if I run CPU intensive program in both of the VMs, the
>> percentage of CPU usage from xentop is almost 100% for both of the
>> VMs. I got confusing because since 2 VCPU shares a single PCPU, the
>> percentage for each one should be around 50%, which is the result if I
>> change the scheduler from credit2 to credit.
>> Does it because credit2 change something or is this a bug for xentop or
>> credit2?
>> Thanks,
>> Yuehai

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