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Re: [Xen-devel] Problems with enabling hypervisor C and P-state control

  • To: "Yu, Ke" <ke.yu@xxxxxxxxx>
  • From: "Niraj Tolia" <ntolia@xxxxxxxxx>
  • Date: Mon, 27 Oct 2008 11:01:04 -0700
  • Cc: "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>, "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Xen Developers <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Mon, 27 Oct 2008 11:01:28 -0700
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On Thu, Oct 23, 2008 at 10:59 PM, Yu, Ke <ke.yu@xxxxxxxxx> wrote:
> After discussing with Jinsong, we got the root cause. You are right, this is 
> xen pm statistics logic issue. when the coordination type is SW_ANY, we only 
> record the first CPU cpufreq change, the other 3 cores within the same 
> dependency domain is ignored, so you only see one core changes every 
> dependency domain.
> The attached patch fix  this issue. could you please have a try? If it works 
> in your platform, we will send out for applying in upstream.

I just applied the patch and while xenpm might be doing the right
thing, I am not completely sure. For example, if I launch a single
VCPU VM, pin it to a core, and launch a CPU intensive task on it, ALL
four cores on the socket are reported to switch into P0. However, from
what I understand about this processor (Xeon E7330), only two of them
should. Like vanilla Linux, the other two should be able to operate at
independent voltage/frequency settings. Once again, I am not sure if
this is xenpm's fault or if the underlying frequency control code
isn't able to determine what  CPUs need to switch frequency at the
same time.


Niraj Tolia, Researcher, HP Labs

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