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

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Mark Langsdorf" <mark.langsdorf@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Sat, 1 Sep 2007 08:23:39 +0800
Delivery-date: Fri, 31 Aug 2007 17:24:13 -0700
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Thread-topic: [Xen-devel] [PATCH] 1/2: cpufreq/PowerNow! in Xen: Time and platform changes
>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2007年8月31日 23:26
>On 31/8/07 16:09, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>> Agree, and some of my colleagues currently works on that part (More
>> specifically, Winston Wang and Ke Yu). But one caveat is that C-state
>> is still likely to be changed dynamically due to hardware event, like AC
>> power change on mobile or some monitor logic on server.
>Does this affect the available C states, or the current C state of a CPU? I
>suppose it's the former that matters, since an attempt to deep-sleep may
>start to fail, which would lead to increased power consumption?

Just affect the available C-states and Xen re-evaluates to get new list 
and thus new decision. Actually that event brings Xen back to C0 out 
of any C1...Cn. When Xen starts to handle that event, the CPU is always 
in C0 as a running state. :-)

>Xen should be very easy indeed to make tickless when idle. In fact the
>handler can be disabled on most systems - we just haven't bothered to
>implement that simple bit of logic yet.

Yes, it's much simpler compared to Linux side and will bring obvious 
power saving due to longer C-state residency period.


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