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Re: [Xen-devel] cpu utilization monitoring

To: Karl Rister <kmr@xxxxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] cpu utilization monitoring
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Mon, 11 Sep 2006 20:56:07 +0100
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The hypercall reports the point-of-view of the timeline of that VCPU. The
fact that its timeline may involve running on various different physical
CPUs should not matter, except for cache-warming and other context-switching
costs. The runstate_info interface absolutely does not state that the
reported run time only includes time spent running on the currently assigned
physical CPU.

 -- Keir

On 11/9/06 8:44 pm, "Karl Rister" <kmr@xxxxxxxxxx> wrote:

> Currently in the vcpu_runstate_info structure we have fields that contain the
> time spent when the vcpu is in one of four states.  When trying to determine
> the physical utilization that a vcpu is requiring of the system from libxc we
> make a domctl operation call to the XEN_DOMCTL_getvcpuinfo command.  When
> processing this command we pull the value for the RUNSTATE_running field and
> attribute it to the processor that the vcpu is currently running on.
> I believe that with the new credit scheduler these values are wrong as it is
> possible that the vcpu has time in RUNSTATE_running that was not actually
> spent on the currently running processor.  Is there a separate path through
> the libraries and into Xen that retrieves this information in a more correct
> manner?  Given that a vcpu can migrate among several physical processors in
> the time between samples it seems that a finer grained accounting mechanism
> is needed to correctly report physical utilization of the hardware resources.

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