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[Xen-devel] cpu utilization monitoring

To: Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] cpu utilization monitoring
From: Karl Rister <kmr@xxxxxxxxxx>
Date: Mon, 11 Sep 2006 14:44:23 -0500
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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.

Karl Rister
IBM Linux Performance Team

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