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[Xen-devel] Re: CPU usage for credit2

To: Yuehai Xu <yuehaixu@xxxxxxxxx>
Subject: [Xen-devel] Re: CPU usage for credit2
From: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Date: Fri, 24 Sep 2010 12:38:21 +0100
Cc: "xen-tools@xxxxxxxxxxxxxxxxxxx" <xen-tools@xxxxxxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "yhxu@xxxxxxxxx" <yhxu@xxxxxxxxx>
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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?

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.

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.


On 23/09/10 14:48, Yuehai Xu wrote:

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?


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