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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: Fri, 28 May 2010 23:05:33 +0800
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Thread-topic: [Xen-devel] [RFC] Physical hot-add cpus and TSC

>-----Original Message-----
>From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
>Sent: Friday, May 28, 2010 10:52 PM
>To: Jiang, Yunhong; Keir Fraser; Xen-Devel (xen-devel@xxxxxxxxxxxxxxxxxxx); Ian
>Subject: RE: [Xen-devel] [RFC] Physical hot-add cpus and TSC
>> b) With the patch:
>> After add:
>> (XEN) TSC marked as reliable, warp = 407 (count=12)
>> (XEN) TSC marked as reliable, warp = 444 (count=17)
>> (XEN) TSC marked as reliable, warp = 525 (count=19)
>Hi Yunhong --
>Does this continue to grow?  I'm concerned that
>the hot-added CPU might be skewing as well?
>I didn't think this was possible with an Invariant
>TSC machine but maybe something in the hot-add
>isolation electronics changes the characteristics
>of the clock signal?

I just looped 10 times, I will try with 1000 loops next Monday.
I suspect there are any isolation electronics for hot-add. Basically each CPU 
can be hot-added except socket 0. But yes, I can have a look on it.


>Please try:
>for i in {0..1000}; do xm debug-key t; sleep 3; done; \
>xm dmesg | tail
>then wait an hour, and see how large the warp is.
>Hopefully the trend (407,444,525) is a coincidence.

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