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| author | Andy Lutomirski <luto@MIT.EDU> | 2011-05-23 09:31:25 -0400 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2011-05-24 14:51:28 +0200 |
| commit | 057e6a8c660e95c3f4e7162e00e2fee1fc90c50d (patch) | |
| tree | 5c0a81327964affd44137754b64fbaf93ceba6fa /arch/Kconfig | |
| parent | 8c49d9a74bac5ea3f18480307057241b808fcc0c (diff) | |
| download | kernel_samsung_espresso10-057e6a8c660e95c3f4e7162e00e2fee1fc90c50d.zip kernel_samsung_espresso10-057e6a8c660e95c3f4e7162e00e2fee1fc90c50d.tar.gz kernel_samsung_espresso10-057e6a8c660e95c3f4e7162e00e2fee1fc90c50d.tar.bz2 | |
x86-64: Remove unnecessary barrier in vread_tsc
RDTSC is completely unordered on modern Intel and AMD CPUs. The
Intel manual says that lfence;rdtsc causes all previous instructions
to complete before the tsc is read, and the AMD manual says to use
mfence;rdtsc to do the same thing.
From a decent amount of testing [1] this is enough to make rdtsc
be ordered with respect to subsequent loads across a wide variety
of CPUs.
On Sandy Bridge (i7-2600), this improves a loop of
clock_gettime(CLOCK_MONOTONIC) by more than 5 ns/iter.
[1] https://lkml.org/lkml/2011/4/18/350
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/%3C1c158b9d74338aa5361f96dd473d0e6a58235302.1306156808.git.luto%40mit.edu%3E
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/Kconfig')
0 files changed, 0 insertions, 0 deletions