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Re: [Xen-users] xentop cpu utilization

To: "XenUsers" <xen-users@xxxxxxxxxxxxxxxxxxx>, "jd" <jdsw2002@xxxxxxxxx>
Subject: Re: [Xen-users] xentop cpu utilization
From: "Nick Couchman" <Nick.Couchman@xxxxxxxxx>
Date: Thu, 14 Feb 2008 06:17:02 -0700
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No, I don't think so.  Based on my experience 1 vcpu has a maximum utilization of one physical CPU core at any given time.  Think about what you're asking the machine to do - present a standardized hardware layer to the guest that includes a single CPU, but actually have it act as an SMP box splitting tasks between multiple CPUs.  I suppose it could be done, but I'm not sure it makes a whole lot of sense.
 
While there does seem to be a limit of 1 vcpu per physical cpu at any given point in time, the hypervisor may juggle that vCPU around between different physical CPU cores or idle that particular vCPU while a vCPU from another of your domUs gets the CPU core(s).  Also, XEN will let you assign more vCPUs than you have physical CPU cores, because you're basically just creating another vCPU for which XEN has to create time on the physical cores, like having more domUs running than you have CPU cores.
 
-Nick

>>> On 2008/02/14 at 03:29, jd <jdsw2002@xxxxxxxxx> wrote:
Hi
 
   Can someone please confirm the following.

-- Xentop shows physical cpu utilization
  
-- With one vcpu, can cpu utilization be > 100% ? i.e
use more than one processor ?
   or if I have 4 cpus and one vm with 2 vcpu
declared. Can the utilization go over 200% ?
    I am assuming that it can not go. But would
appreciate if some one can confirm.

Thanks
/Jd


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