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List:       linux-kernel
Subject:    Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64
From:       Borislav Petkov <bp () alien8 ! de>
Date:       2013-06-30 22:00:04
Message-ID: 20130630220004.GA23124 () pd ! tnic
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On Sat, Jun 29, 2013 at 04:56:30PM -0700, Wedson Almeida Filho wrote:
> On Fri, Jun 28, 2013 at 7:09 AM, Borislav Petkov <bp@alien8.de> wrote:
> 
> > Btw, do we have any perf data showing any improvements from this patch?
> 
> I wrote a simple test the measures the time it takes to acquire and
> release  an uncontended mutex (i.e., we always take the fast path)
> 100k times. I ran it a few times, the original code averages
> 2.743436ms, and the new code averages 2.101098ms, so it's about 23% improvement.

Microbenchmark results tend to be misleading in such situations. Rather,
it would be much closer to reality if you traced a real workload like a
simple kernel build, for example, with and without your patch.

I.e., something like

perf stat --repeat 5 ./build-kernel.sh

and take a look at what the perfcouters are saying in both cases.

> I also think the code looks cleaner this way.

No doubt.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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