From: Andy Lutomirski <luto@MIT.EDU>
Date: Mon, 23 May 2011 13:31:26 +0000 (-0400)
Subject: x86-64: Don't generate cmov in vread_tsc
X-Git-Tag: v3.0-rc1~128^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3729db5ca2b2000c660e5a5d0eb68b1053212cab;p=pandora-kernel.git

x86-64: Don't generate cmov in vread_tsc

vread_tsc checks whether rdtsc returns something less than
cycle_last, which is an extremely predictable branch.  GCC likes
to generate a cmov anyway, which is several cycles slower than
a predicted branch.  This saves a couple of nanoseconds.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Borislav Petkov <bp@amd64.org>
Link: http://lkml.kernel.org/r/%3C561280649519de41352fcb620684dfb22bad6bac.1306156808.git.luto%40mit.edu%3E
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---

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