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[Xen-devel] [RFC] Correct/fast timestamping in apps under Xen [2 of 4]:

To: "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] [RFC] Correct/fast timestamping in apps under Xen [2 of 4]: rdtscp
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Fri, 2 Oct 2009 10:51:11 -0700 (PDT)
Cc: kurt.hackel@xxxxxxxxxx, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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=============
Premise 2: A small but growing percentage of servers running
Xen implement the rdtscp instruction but Xen does not and
will not expose this instruction to guest OSes.
=============

Issues:
a) What processors support rdtscp?  Intel's Nehalem is the
   first Intel processor that does.  Many (all?) recent AMD
   processors do.
b) Will rdtscp be pulled from future processors?  (appears
   unlikely)
c) Will Xen ever need to expose rdtscp to guest OS's?
d) Will the TSC_AUX part of rdtscp ever be needed to do
   something other than communicate some form of
   "incarnation" number?

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