[PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks
From: Michael S. Tsirkin
Date: Tue Jan 12 2016 - 17:10:23 EST
mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's
2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs.
So let's use the locked variant everywhere - helps keep the code simple as
well.
While I was at it, I found some inconsistencies in comments in
arch/x86/include/asm/barrier.h
I hope I'm not splitting this up too much - the reason is I wanted to isolate
the code changes (that people might want to test for performance) from comment
changes approved by Linus, from (so far unreviewed) comment change I came up
with myself.
Lightly tested on my system.
Michael S. Tsirkin (3):
x86: drop mfence in favor of lock+addl
x86: drop a comment left over from X86_OOSTORE
x86: tweak the comment about use of wmb for IO
arch/x86/include/asm/barrier.h | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
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MST