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RE: [Xen-devel] Time skew on HP DL785 (and possibly other boxes)

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: RE: [Xen-devel] Time skew on HP DL785 (and possibly other boxes)
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 6 Apr 2009 14:41:22 +0000 (GMT)
Cc: john.v.morris@xxxxxx, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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> Well, my point is a bit out of topic here. Of course your
> concern about cross-node TSC variance still makes sense
> whether or not node affinity is enforced, as long as VM is
> possibly migrated cross-nodes. My point is just that turn
> on 'numa' itself is really not a 'extremely restrictive'
> thing. :-)

Hi Kevin --

I think numa-mode is extremely restrictive because
it makes a 32-way box work like eight 4-way blades.

I think the whole point of HT/QPI is to reduce the
memory latency enough so that a NUMA box does not
look like a NUMA box.  If time synchronization fails
so that this type of box is forced to be partitioned,
the value of HT/QPI is greatly diminished (at least
in a virtualization environment).


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