From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Fri, 24 Apr 2009 07:26:50 +0000 (-0700)
Subject: xen: cache cr0 value to avoid trap'n'emulate for read_cr0
X-Git-Tag: v2.6.31-rc1~410^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a789ed5fb6d0256c4177c2cc27e06520ddbe4d4c;p=pandora-kernel.git

xen: cache cr0 value to avoid trap'n'emulate for read_cr0

stts() is implemented in terms of read_cr0/write_cr0 to update the
state of the TS bit.  This happens during context switch, and so
is fairly performance critical.  Rather than falling back to
a trap-and-emulate native read_cr0, implement our own by caching
the last-written value from write_cr0 (the TS bit is the only one
we really care about).

Impact: optimise Xen context switches
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
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