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Re: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform

To: "Rik van Riel" <riel@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Fri, 31 Aug 2007 09:41:47 +0100
Cc: Keir Fraser <keir@xxxxxxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Mark Langsdorf <mark.langsdorf@xxxxxxx>
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>Here is the missing piece of the puzzle.   A platform
>hypercall operation to get system wide idle time.

Two things I'm not clear about here:
- How is the caller going to be able to associate the logical CPU numbers
  returned with vCPU numbers?
- How is the caller supposed to deal with logical CPUs it has no vCPU for?

I continue to think that it is not reasonable to expect vCPUs to be pinned just
for the purpose of doing frequency control (and even then I don't think there's
a guaranteed association between vCPU and logical CPU numbers), as much
as I don't think it is a good idea to require dom0 to have as many vCPUs as
there are logical CPUs (which isn't even possible on systems with >32 logical


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