x86-64: Don't generate cmov in vread_tsc
authorAndy Lutomirski <luto@MIT.EDU>
Mon, 23 May 2011 13:31:26 +0000 (09:31 -0400)
committerThomas Gleixner <tglx@linutronix.de>
Tue, 24 May 2011 12:51:28 +0000 (14:51 +0200)
commit3729db5ca2b2000c660e5a5d0eb68b1053212cab
treea8b038145eadd067f92798adb4292532eccedfba
parent057e6a8c660e95c3f4e7162e00e2fee1fc90c50d
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>
arch/x86/kernel/tsc.c