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

Jeff Garzik
2007-06-09T20:23:49Z

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