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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 10:30:51 +0100
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On 30/8/07 07:41, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> a) Current approach is simple to let Dom0 conduct frequency
> change. That should be OK in the start, but at the same time we
> should also consider the on-demand governor within Xen itself.
> Xen can always get first-hand data about domain status, while
> dom0 (either user-level or in-kernel) can't achieve in time. Fine-
> grained frequency change is more likely to be achieved within
> Xen directly.

Personally I'm a fan of doing it in dom0 userspace, although doing it within
Xen can also be argued for. Doing it in dom0 kernel doesn't seem very
attractive apart from the obvious pragmatic advantage that all the code is
already in the Linux kernel. :-)

If we're doing it in the Linux kernel, I don't see much point in hacking up
the defunct powernow (or equivalent Intel) code. Why not fix the generic
acpi-cpufreq.c? That is supposed to work on any modern CPU. I'm not sure the
2.6.18 version is new enough, but I'd rather see a backported and fixed
version of that file, rather than bother to maintain modified versions of
obsolete source files.

 -- Keir

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