Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks
Date	2016-01-12 23:30 +0100
Message-ID	<qQfBT-7kg-5@gated-at.bofh.it> (permalink)
References	<qQfsd-7eN-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 01/12/16 14:10, Michael S. Tsirkin wrote:
> 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
> 

I would like to get feedback from the hardware team about the
implications of this change, first.

	-hpa

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[PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-12 23:20 +0100
  Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks "H. Peter Anvin" <hpa@zytor.com> - 2016-01-12 23:30 +0100

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