Re: cpu utilization monitoring

[Karl Rister <kmr@us.ibm.com>]

Is there a more appropriate interface for collecting this information then?  I 
would like to be able to sample on an some interval (say 3 or 5 seconds) and 
be able to see the amount of time a vcpu spent running on the individual 
physical processors during that time.

On Monday 11 September 2006 2:56 pm, Keir Fraser wrote:
> 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@us.ibm.com> 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.

-- 
Karl Rister
IBM Linux Performance Team
kmr@us.ibm.com