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Re: [Xen-devel] cpufreq status information

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] cpufreq status information
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 08 Sep 2008 15:00:47 +0100
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On 8/9/08 14:50, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> The intent is to expose the frequency of the pCPU the particular vCPU
>> is currently running on, perhaps only in Dom0.
> Then you have to pin dom0 vCPU to corresponding pCPU, and have
> dom0 with same number as pCPU. I don't think such limitation
> necessary for just retrieving some pCPU information.
> Or if you still enable vcpu migration, you have to fake virtual freq
> change notification within dom0 at vcpu migration as pCPU may
> scale its own freq individually.

Greater virtualisation of cpufreq info (making it available to arbitrary
guests, with pcpu->vcpu remapping) is just not very useful in my opinion.
It's one of those features that more hacker-ish users might think they want
to decorate their desktop.

After all, guest performance is at least as affected by CPU (and other
resources) contention from other guests as it is by power-management
governors in the hyeprvisor. Indeed, if the governors are doing their job
right then guest performance should not be considerably impacted by them
even in absolute terms.

 -- Keir

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