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Re: [Xen-devel] strange CPU utilization, could related to credit schedul

To: tinnycloud <tinnycloud@xxxxxxxxxxx>
Subject: Re: [Xen-devel] strange CPU utilization, could related to credit schedule ?
From: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Date: Wed, 12 Jan 2011 16:41:07 +0000
Cc: xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Where is that 85% number coming from -- is this from within the VM, or
from xentop?

If it's Windows reporting from within the VM, one hypothesis is that
it has to do with processing and running with virtual time.  It may
simply be a side effect of the VM only getting a small percentage of
the cpu.

If it's xentop, it's probably the vm reacting somehow to getting only
a small percentage of the CPU.  We saw something like this with early
versions of Windows 2k3, but that problem was addressed in later
service packs.  At any rate, to find out what Windows is doing would
require a bit more investigation. :-)


On Wed, Jan 12, 2011 at 2:41 PM, tinnycloud <tinnycloud@xxxxxxxxxxx> wrote:
>  Hi Geogre:
>          We have quite strange CPU usage behaivor in one of our DomU(2008
> HVM)
>          Totally, our host has 16 physical CPU, and 9 VMS.
>          Most of time, the all VMs works fine, the CPU usage are low and
> resonable,
> But at every high workload time(say 9:00-11:00AM, there are 8 VMs, each is a
> web server,
> cutomers accesses the page at this time), we login into the 9th VM which
> is idle, find that
> its CPU usage is at 85%, doesn't make any sense since we have no task
> running, also the
> usage distrbutes evenly across most of the processes.
>         I wonder if it relates to CPU schedule algorithm in Xen.
>         After go
> through http://lists.xensource.com/archives/html/xen-devel/2010-07/msg00414.html
>         I can't figure out any assumptiones explains our situation.
>         So what do u think of this?
>         Many thanks.
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