linux-kernel - Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64

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Message-ID: <20130630220004.GA23124@pd.tnic>
Date:	Mon, 1 Jul 2013 00:00:04 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Wedson Almeida Filho <wedsonaf@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64

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@...en8.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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