linux-kernel - Re: [PATCH v3] crypto: crc32c-pclmul

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Date:	Sat, 21 Jun 2014 02:42:28 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	George Spelvin <linux@...izon.com>
Cc:	tim.c.chen@...ux.intel.com, james.guilford@...el.com,
	JBeulich@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] crypto: crc32c-pclmul - Shrink K_table to 32-bit words

On Fri, Jun 06, 2014 at 11:08:58PM -0400, George Spelvin wrote:
> There's no need for the K_table to be made of 64-bit words.  For some
> reason, the original authors didn't fully reduce the values modulo the
> CRC32C polynomial, and so had some 33-bit values in there.  They can
> all be reduced to 32 bits.
> 
> Doing that cuts the table size in half.  Since the code depends on both
> pclmulq and crc32, SSE 4.1 is obviously present, so we can use pmovzxdq
> to fetch it in the correct format.
> 
> This adds (measured on Ivy Bridge) 1 cycle per main loop iteration
> (CRC of up to 3K bytes), less than 0.2%.  The hope is that the reduced
> D-cache footprint will make up the loss in other code.
> 
> Two other related fixes:
> * K_table is read-only, so belongs in .rodata, and
> * There's no need for more than 8-byte alignment
> 
> Acked-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: George Spelvin <linux@...izon.com>

Patch applied.  Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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