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Re: [Xen-ia64-devel] problems with smp


  • To: "Alex Williamson" <alex.williamson@xxxxxx>
  • From: "David Brown" <dmlb2000@xxxxxxxxx>
  • Date: Thu, 8 Feb 2007 15:42:39 -0800
  • Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 08 Feb 2007 15:43:30 -0800
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  • List-id: Discussion of the ia64 port of Xen <xen-ia64-devel.lists.xensource.com>

   All of the CPUs exposed to dom0 and domUs are virtual CPUs.  Xen
schedules virtual CPUs across the physical CPUs just like a bare metal
OS schedules processes across physical CPUs.  The xm top output shows
vCPU processor usage across all the vCPUs in a domain.  The CPU% shown
is the percentage of physical CPU time taken.  So 100% means the domain
is consuming all the time of one physical CPU.  A 4-way domain might
consume up to 400%.  One vCPU cannot consume more than one physical CPU,
so if you have less vCPUs (across all domains) than you do pCPUs, then
you won't be able to fully utilize the extra pCPUs.  Does that help?
Thanks,

Yes, thanks.

So, my dual itanium 2 box running dom0 and 8 domU's, and xm top is
showing that the dom0 and one of the domU's are using %40 each and the
other 7 domU's are showing <10% (this almost sounds like a high school
math problem ;)) is not actually maxed out... there's a slowdown
somewhere else in the system then because really adding up the
percentages should equal to 200% if the processors were maxed out.

At least that's what I think is going on...

- David Brown

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