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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>
Subject: Re: [Xen-devel] [RFC] Physical hot-add cpus and TSC
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 26 May 2010 18:29:40 +0100
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Thread-topic: [Xen-devel] [RFC] Physical hot-add cpus and TSC
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On 26/05/2010 17:44, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> True at the moment, but can we not just whack the TSC of the newly
>> added CPU  on the head when it is brought online, to match the
>> boot CPU?
> Possibly... but the code for whacking the TSC of a CPU after
> C3-state results in a TSC value that is poorly-aligned with other
> running TSCs.  If there is a better way for "whacking" that
> results in a nearly-perfectly-aligned TSC (that would pass
> a "tsc warp test"), that is an option.

But what we do in 4.0 is whack all the TSCs at boot time... How is this any

 -- Keir

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