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Re: [Xen-devel] [RFC] Physical hot-add cpus and TSC

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel (xen-devel@xxxxxxxxxxxxxxxxxxx)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] Physical hot-add cpus and TSC
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 26 May 2010 18:51:45 +0100
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On 26/05/2010 18:39, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> But what we do in 4.0 is whack all the TSCs at boot time... How is this
>> any different?
> I don't think we do that anymore, at least not when the
> underlying machine is deemed to have a stable TSC
> (Invariant TSC or constant/nonstop TSC with max_cstate<3).

Hm, yep, looks like we skip it when we detect 'reliable tscs'. So on modern
x86 that means we do not modify TSCs in Xen ever.

 -- Keir

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