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

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Mark Langsdorf <mark.langsdorf@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Thu, 30 Aug 2007 11:12:28 +0100
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Thread-topic: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes
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On 30/8/07 10:45, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Sure, some experiment can be done later to compare dom0 userspace
> and in-xen governor. Agree that in-kernel dom0 approach is not
> charming because anyway it needs help from either user-level or xen
> for global view.
> Actually finally we may take both. Xen takes simple heuristic policy
> with user-level governor to adjust with more complex and flexible
> policies based on domain behaviors. :-)

There is the problem, though, that most modern CPUs will need cpufreq info
to be parsed out of the ACPI DSDT. And Xen can't do that itself unaided.
Pushing down some form of cpufreq info table to Xen *is* an option though,
but we'd need more custom dom0 kernel code to do that. Or we'd need to do it
from a userspace program.

 -- Keir

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