linux-kernel - Re: [PATCH] x86: Add optimized popcnt variants

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Message-ID: <4B875BBD.4060104@zytor.com>
Date:	Thu, 25 Feb 2010 21:27:25 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Michal Marek <mmarek@...e.cz>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	Roland Dreier <rdreier@...co.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH] x86: Add optimized popcnt variants

On 02/23/2010 11:06 AM, Borislav Petkov wrote:
> 
> Ok, here you go.
> 
> --
> From: Borislav Petkov <borislav.petkov@....com>
> Date: Thu, 11 Feb 2010 00:48:31 +0100
> Subject: [PATCH] x86: Add optimized popcnt variants
> 
> Add support for the hardware version of the Hamming weight function,
> popcnt, present in CPUs which advertize it under CPUID, Function
> 0x0000_0001_ECX[23]. On CPUs which don't support it, we fallback to the
> default lib/hweight.c sw versions.
> 
> A synthetic benchmark comparing popcnt with __sw_hweight64 showed almost
> a 3x speedup on a F10h machine.
> 
> Signed-off-by: Borislav Petkov <borislav.petkov@....com>

OK, this patch looks pretty good now, but I'm completely lost as to what
the baseline of this patch is supposed to be.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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