linux-kernel - Re: [PATCH 2/3] [CRYPTO] Add optimized SHA-1 implementation for i486+

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Message-ID: <466B0C3F.3040300@garzik.org>
Date:	Sat, 09 Jun 2007 16:23:27 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Matt Mackall <mpm@...enic.com>
CC:	Benjamin Gilbert <bgilbert@...cmu.edu>, akpm@...ux-foundation.org,
	herbert@...dor.apana.org.au, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] [CRYPTO] Add optimized SHA-1 implementation for i486+

Matt Mackall wrote:
> On Fri, Jun 08, 2007 at 05:42:53PM -0400, Benjamin Gilbert wrote:
>> Add x86-optimized implementation of the SHA-1 hash function, taken from
>> Nettle under the LGPL.  This code will be enabled on kernels compiled for
>> 486es or better; kernels which support 386es will use the generic
>> implementation (since we need BSWAP).
>>
>> We disable building lib/sha1.o when an optimized implementation is
>> available, as the library link order for x86 (and x86_64) would otherwise
>> ignore the optimized version.  The existing optimized implementation for ARM
>> does not do this; the library link order for that architecture appears to
>> favor the arch/arm/ version automatically.  I've left this situation alone
>> since I'm not familiar with the ARM code, but a !ARM condition could be
>> added to CONFIG_SHA1_GENERIC if it makes sense.
>>
>> The code has been tested with tcrypt and the NIST test vectors.
> 
> Have you benchmarked this against lib/sha1.c? Please post the results.
> Until then, I'm frankly skeptical that your unrolled version is faster
> because when I introduced lib/sha1.c the rolled version therein won by
> a significant margin and had 1/10th the cache footprint.

Yes. And it also depends on the CPU as well.  Testing on a server-class 
x86 CPU (often with bigger L2, and perhaps even L1, cache) will produce 
different result than from popular but less-capable "value" CPUs.

	Jeff


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