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

To: MaoXiaoyun <tinnycloud@xxxxxxxxxxx>
Subject: Re: [Xen-devel] Too much VCPUS makes domU high CPU utiliazation
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Wed, 18 May 2011 12:39:50 -0400
Cc: george.dunlap@xxxxxxxxxxxxx, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Thu, May 19, 2011 at 12:19:11AM +0800, MaoXiaoyun wrote:
> HI: 
>      I have a host with 16 physical CPUS. Dom0 has 4 VCPUS.
>     When only start a domU-A(windows 2003 x86 64rc 2) with 16 VCPUS, it 
> starts quickly and eveything is fine.
>      But if I first start domU-B, which has 2VCPUS, domU-C 4VCPUS, and domU-D 
> 8 VCPUS,  later I start DomUA again,
> (so we have total 34 VCPUS, plus dom0), it will takes very long time for 
> domU-A to start ,and during the start, its CPU
> utilizaiton is around 800% from xm top, after its start, it response very 
> slow in VNC, ans CPU utiliazation keeps high.
> And right after I destoy other 3 domUs, domUA CPU drops to normal.

You might be missing some patches for the Dom0 irq round-robin code. Is your 
Dom0 2.6.32 pvops?
Look for these patches in your git log:
  xen: events: Remove redundant clear of l2i at end of round-robin loop
      xen: events: Make round-robin scan fairer by snapshotting each l2 word 
once only
      xen: events: Clean up round-robin evtchn scan.
      xen: events: Make last processed event channel a per-cpu variable.
      xen: events: Process event channels notifications in round-robin order.

>    It might relate to CPU schedule, btw, my xen is 4.0.1.
>   Any comments? 

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