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

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, "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: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 31 May 2010 17:30:30 -0700 (PDT)
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> BTW, I notice one more thing, when system booting w/o hotplug, the warp
> is 0. However, after I return back after weekend, I noticed the warp is
> 182. Because I did the hotplug action before getting the warp, I'm not
> sure if it's caused by the hotplug action, or the system TSC will drift
> very slowly.
>  (XEN) TSC marked as reliable, warp = 182 (count=2)

Hmmm... I'm much more worried about this case and would
like to understand this better.  If this is reproducible
on real-world QPI systems, and there is no way to a priori
determine that "this is a system where even though the
Invariant TSC bit is set, this system may drift", then
there is no way Invariant TSC can be exposed to a guest.

/me can hear Jeremy biting his tongue hard to avoid
saying "I told you so". ;-)


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