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

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes
From: Rik van Riel <riel@xxxxxxxxxx>
Date: Fri, 31 Aug 2007 09:50:48 -0400
Cc: Mark Langsdorf <mark.langsdorf@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxxxxxxxx>
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Tian, Kevin wrote:

b) Code duplication is definitely bad. But if finally xen-based governor is proved to be with best power saving cap, why not?

Because the larger the hypervisor is, the less practical it
becomes to maintain.  The current Xen hypervisor already has
bugs in its copied-from-Linux code that were fixed in Linux
after the code was copied.

A small hypervisor is nice, but Xen is painfully large to

d) I guess final power saving of cpufreq (either approach) is not obvious, since average CPU utilization should be higher than native which is the goal of virtualization. C-state may be more interesting.

This makes a lot of sense.  C-state makes a big impact on
power usage and can be implemented inside the idle loop
relatively easily.

Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.

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