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Re: [Xen-devel] [RFC] Correct/fast timestamping in apps under Xen [1 of

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] Correct/fast timestamping in apps under Xen [1 of 4]: Reliable TSC
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Thu, 8 Oct 2009 10:13:45 +0100
Cc: Fitzhardinge <jeremy@xxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jeremy, "kurt.hackel@xxxxxxxxxx" <kurt.hackel@xxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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At 22:07 +0100 on 07 Oct (1254953275), Dan Magenheimer wrote:
> Admittedly, this doesn't guarantee that a multi-socket
> platform obeys invariance, but apparently this
> feature utilizes a crystal available externally
> to the socket so it is easy to leverage in a
> system design to ensure invariance across
> multiple sockets, or even across multiple enclosures
> that are all on a QPI link.  So system designers
> (other than perhaps for the very largest superNUMA
> machines) would be silly to not use it.

Oh, that's reassuring.  System designers would never do something that
silly.  :)

If linux relies on it, that's a good sign, but surely we shouldn't get
rid of any existing correction mechanisms. 

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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