linux-kernel - Re: [PATCH] Performance Improvement in CRC16 Calculations.

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Date:   Fri, 10 Aug 2018 12:23:06 -0700
From:   Joe Perches <joe@...ches.com>
To:     Jeff Lien <jeff.lien@....com>, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-block@...r.kernel.org,
        linux-scsi@...r.kernel.org
Cc:     herbert@...dor.apana.org.au, tim.c.chen@...ux.intel.com,
        martin.petersen@...cle.com, david.darrington@....com,
        jeff.furlong@....com
Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations.

On Fri, 2018-08-10 at 14:12 -0500, Jeff Lien wrote:
> This patch provides a performance improvement for the CRC16 calculations done in read/write
> workloads using the T10 Type 1/2/3 guard field.  For example, today with sequential write
> workloads (one thread/CPU of IO) we consume 100% of the CPU because of the CRC16 computation
> bottleneck.  Today's block devices are considerably faster, but the CRC16 calculation prevents
> folks from utilizing the throughput of such devices.  To speed up this calculation and expose
> the block device throughput, we slice the old single byte for loop into a 16 byte for loop,
> with a larger CRC table to match.  The result has shown 5x performance improvements on various
> big endian and little endian systems running the 4.18.0 kernel version.

Thanks.

This seems a sensible tradeoff for the 4k text size increase.

> diff --git a/crypto/crct10dif_common.c b/crypto/crct10dif_common.c

[]

trivia:

> +static const __u16 t10_dif_crc_table[16][256] = {
> +	{
> +	0x0000u, 0x8BB7u, 0x9CD9u, 0x176Eu, 0xB205u, 0x39B2u, 0x2EDCu, 0xA56Bu,

All the 'u's are unnecessary visual noise.