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RE: [Xen-devel] Too much VCPUS makes domU high CPU utiliazation

To: MaoXiaoyun <tinnycloud@xxxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Too much VCPUS makes domU high CPU utiliazation
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Fri, 20 May 2011 07:29:55 +0800
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Thread-topic: [Xen-devel] Too much VCPUS makes domU high CPU utiliazation
>From: MaoXiaoyun [mailto:tinnycloud@xxxxxxxxxxx] 
>Sent: Friday, May 20, 2011 12:24 AM
>> does same thing happen if you launch B/C/D after A?
>From test aspects, not really, all domains CPU Util are low.
>It looks like this only happen in the process of domain A booting, and result 
>in quite long time to boot.

One possible reason is the lock contention at the boot time. If the lock holder
is preempted unexpectedly and lock waiter continues to consume cycles, the
boot progress could be slow.

Which kernel version are you using? Does a different kernel version expose 
same problem?

>One thing to correct, today even I destory B/C/D, domain A still comsume 800% 
>CPU for quite a long time till now I am writing 
>this mail.

So this phenomenon is intermittent? In your earlier mail A is back to normal
after you destroyed B/C/D, and this time the slowness continues. 

>Another strang thing is seems all VCPUS of domainUA, are running only on even 
>number Physicals CPUS(that is 0, 2,4...),
>where explains where CPU Util is 800%.  But I don't understand whether this is 
>designed to. 

Are there any hard limitation you added from the configuration file? Or do you
observe this weird affinity all the time or occasionally? It looks strange to me
that scheduler will consistently keep such affinity if you don't assign it 

you may want to run xenoprof to sampling domain A to see its hot points, or
use xentrace to trace VM-exit events to deduce from another angle.


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