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

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, 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: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Date: Tue, 1 Jun 2010 09:40:44 +0800
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Thread-topic: [Xen-devel] [RFC] Physical hot-add cpus and TSC
Yes, I'm confused by this also.
It will takes to this weekend so that I can try it again.

--jyh

>-----Original Message-----
>From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
>Sent: Tuesday, June 01, 2010 8:31 AM
>To: Jiang, Yunhong; Keir Fraser; Xen-Devel (xen-devel@xxxxxxxxxxxxxxxxxxx); Ian
>Pratt
>Subject: RE: [Xen-devel] [RFC] Physical hot-add cpus and TSC
>
>> 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". ;-)
>
>Dan

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