linux-kernel - Re: [PATCH v5 0/3] lib: find_*

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Date:	Mon, 23 Feb 2015 16:40:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yury Norov <yury.norov@...il.com>
Cc:	linux@...izon.com, klimov.linux@...il.com,
	linux@...musvillemoes.dk, davem@...emloft.net, dborkman@...hat.com,
	hannes@...essinduktion.org, laijs@...fujitsu.com,
	msalter@...hat.com, takahiro.akashi@...aro.org, tgraf@...g.ch,
	valentinrothberg@...il.com, linux-kernel@...r.kernel.org,
	chris@...is-wilson.co.uk
Subject: Re: [PATCH v5 0/3] lib: find_*_bit reimplementation

On Sun, 22 Feb 2015 20:24:14 +0300 Yury Norov <yury.norov@...il.com> wrote:

> This patchset does rework find_bit functions family to achieve better
> performance, and decrease size of text. All rework is done in patch 1.
> Patches 2 and 3 are about code moving and renaming.
> 
> It was boot-tested on x86_64 and MIPS (big-endian) machines.
> Performance tests were ran on userspace with code like this:
> 
> 	/* addr[] is filled from /dev/urandom */
> 	start = clock();
> 	while (ret < nbits)
> 		ret = find_next_bit(addr, nbits, ret + 1);
> 
> 	end = clock();
> 	printf("%ld\t", (unsigned long) end - start);
> 
> On Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz measuremets are next:
> (for find_next_bit, nbits is 8M, for find_first_bit - 80K)
> 
> 	find_next_bit:		find_first_bit:
> 	new	current		new	current
> 	26932	43151		14777	14925
> 	26947	43182		14521	15423
> 	26507	43824		15053	14705
> 	27329	43759		14473	14777
> 	26895	43367		14847	15023
> 	26990	43693		15103	15163
> 	26775	43299		15067	15232
> 	27282	42752		14544	15121
> 	27504	43088		14644	14858
> 	26761	43856		14699	15193
> 	26692	43075		14781	14681
> 	27137	42969		14451	15061
> 	...			...
> 
> find_next_bit performance gain is 35-40%;
> find_first_bit - no measurable difference.
> 
> On ARM machine, there is arch-specific implementation for find_bit.
> To disable it, and use generic one, please apply next patch:

I avoid putting patches into changelogs because in some situations
patch(1) tries to apply it when you apply the real patch.  Maybe you
can share the userspace test harness with someone who has access to an
arm machine?

Patches 2 and 3 are missing your signed-off-by:.  I added it to my
copies of those patches.

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