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

From	"Michael S. Tsirkin" <mst@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks
Date	2016-01-26 09:30 +0100
Message-ID	<qV7aG-1qe-7@gated-at.bofh.it> (permalink)
References	<qQfsd-7eN-3@gated-at.bofh.it> <qQfBT-7kg-5@gated-at.bofh.it>
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On Tue, Jan 12, 2016 at 02:25:24PM -0800, H. Peter Anvin wrote:
> 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
> 

Hi hpa,
Any luck getting some feedback on this one?

Thanks,

-- 
MST

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Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-26 09:30 +0100
  Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks "H. Peter Anvin" <hpa@zytor.com> - 2016-01-26 22:40 +0100
    Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-27 15:10 +0100
      Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-27 15:20 +0100
      Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks Peter Zijlstra <peterz@infradead.org> - 2016-01-27 15:20 +0100

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