linux-kernel - Re: [RFC] change non-atomic bitops method

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Message-ID: <20150203103932.GA14259@node.dhcp.inet.fi>
Date:	Tue, 3 Feb 2015 12:39:32 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>,
	"'arnd@...db.de'" <arnd@...db.de>,
	"'linux-arch@...r.kernel.org'" <linux-arch@...r.kernel.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'linux@....linux.org.uk'" <linux@....linux.org.uk>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC] change non-atomic bitops method

On Tue, Feb 03, 2015 at 03:17:30AM +0200, Kirill A. Shutemov wrote:
> Results for 10 runs on my laptop -- i5-3427U (IvyBridge 1.8 Ghz, 2.8Ghz Turbo
> with 3MB LLC):

I've screwed up the inner loop condition and step. As result the benchmark
touches the same cache line 8 times and scan SIZE/8 of memory. Fixed test
is in attach.
				Avg		Stddev
baseline			14.0663		0.0182
-DCHECK_BEFORE_SET		13.8594		0.0458
-DCACHE_HOT			12.3896		0.0867
-DCACHE_HOT -DCHECK_BEFORE_SET	11.7480		0.2497

And now it's faster *with* the check. Sometimes CPU is just too clever. ;)

-- 
 Kirill A. Shutemov

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