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Re: [Xen-devel] CPU Usage Discrepancies

To: Pradeep Vincent <pradeep.vincent@xxxxxxxxx>
Subject: Re: [Xen-devel] CPU Usage Discrepancies
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 07 Mar 2007 08:32:49 +0000
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On 7/3/07 01:11, "Pradeep Vincent" <pradeep.vincent@xxxxxxxxx> wrote:

> Linux counts all the nanosecs not accounted by the hypervisor towards
> "stolen" or "blocked" as its own usage. This should include all the
> time spent in the hypervisor in the context of a particular Vcpu - The
> hypervisor counts nsecs as "stolen" or "blocked" only after the Vcpu's
> state is changed (from running to something else)  So most part of the
> hypervisor's CPU usage should be accounted for the same way by xm and
> by /proc/stat on guests as they both use the same "stolen" and
> "blocked" nsecs as accounted for and maintained by the hypervisor.
> Like you said context switch overhead isn't accounted for accurately
> but hypervisor's cpu usage accounting suffers from the same problem
> and to the same extent. Even if this isn't the case,  context switch
> cpu usage can't account for this big a difference.

It sounds like you could track this one down yourself and post a patch if
you find a bug? :-)

 -- Keir

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