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

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Date:   Thu, 16 Aug 2018 10:22:04 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Jeffrey Lien <Jeff.Lien@....com>,
        Eric Biggers <ebiggers@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        David Darrington <david.darrington@....com>,
        Jeff Furlong <jeff.furlong@....com>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations.

Hi,
Rather than present this formerly as an alternate patch, attached is a
clean-up of my patch which uses the variable size table proposed by
Joe Perches <joe@...ches.com> and is based on the original patch that
started this thread.

Doug Gilbert

On 2018-08-16 10:02 AM, Jeffrey Lien wrote:
> Eric,
> We did not test the slice by 4 or 8 tables.  I'm not sure of  the value of doing that since the slice by 16 will provide the best performance gain.   If I'm missing anything here, please let me know.
> 
> I'm working on a new version of the patch based on the feedback from others and will also change the pointer variables to start with p and fix the indenting you mentioned below in the new version of the patch.
> 
> Thanks
> 
> Jeff Lien
> 
> -----Original Message-----
> From: Eric Biggers [mailto:ebiggers@...nel.org]
> Sent: Friday, August 10, 2018 3:16 PM
> To: Jeffrey Lien <Jeff.Lien@....com>
> Cc: linux-kernel@...r.kernel.org; linux-crypto@...r.kernel.org; linux-block@...r.kernel.org; linux-scsi@...r.kernel.org; herbert@...dor.apana.org.au; tim.c.chen@...ux.intel.com; martin.petersen@...cle.com; David Darrington <david.darrington@....com>; Jeff Furlong <jeff.furlong@....com>
> Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations.
> 
> On Fri, Aug 10, 2018 at 02:12:11PM -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.
>>
>> FIO Sequential Write, 64K Block Size, Queue Depth 64
>> BE Base Kernel:        bw=201.5 MiB/s
>> BE Modified CRC Calc:  bw=968.1 MiB/s
>> 4.80x performance improvement
>>
>> LE Base Kernel:        bw=357 MiB/s
>> LE Modified CRC Calc:  bw=1964 MiB/s
>> 5.51x performance improvement
>>
>> FIO Sequential Read, 64K Block Size, Queue Depth 64
>> BE Base Kernel:        bw=611.2 MiB/s
>> BE Modified CRC calc:  bw=684.9 MiB/s
>> 1.12x performance improvement
>>
>> LE Base Kernel:        bw=797 MiB/s
>> LE Modified CRC Calc:  bw=2730 MiB/s
>> 3.42x performance improvement
> 
> Did you also test the slice-by-4 (requires 2048-byte table) and slice-by-8 (requires 4096-byte table) methods?  Your proposal is slice-by-16 (requires 8192-byte table); the original was slice-by-1 (requires 512-byte table).
> 
>>   __u16 crc_t10dif_generic(__u16 crc, const unsigned char *buffer,
>> size_t len)  {
>> -	unsigned int i;
>> +	const __u8 *i = (const __u8 *)buffer;
>> +	const __u8 *i_end = i + len;
>> +	const __u8 *i_last16 = i + (len / 16 * 16);
> 
> 'i' is normally a loop counter, not a pointer.
> Use 'p', 'p_end', and 'p_last16'.
> 
>>   
>> -	for (i = 0 ; i < len ; i++)
>> -		crc = (crc << 8) ^ t10_dif_crc_table[((crc >> 8) ^ buffer[i]) & 0xff];
>> +	for (; i < i_last16; i += 16) {
>> +		crc = t10_dif_crc_table[15][i[0] ^ (__u8)(crc >>  8)] ^
>> +		t10_dif_crc_table[14][i[1] ^ (__u8)(crc >>  0)] ^
>> +		t10_dif_crc_table[13][i[2]] ^
>> +		t10_dif_crc_table[12][i[3]] ^
>> +		t10_dif_crc_table[11][i[4]] ^
>> +		t10_dif_crc_table[10][i[5]] ^
>> +		t10_dif_crc_table[9][i[6]] ^
>> +		t10_dif_crc_table[8][i[7]] ^
>> +		t10_dif_crc_table[7][i[8]] ^
>> +		t10_dif_crc_table[6][i[9]] ^
>> +		t10_dif_crc_table[5][i[10]] ^
>> +		t10_dif_crc_table[4][i[11]] ^
>> +		t10_dif_crc_table[3][i[12]] ^
>> +		t10_dif_crc_table[2][i[13]] ^
>> +		t10_dif_crc_table[1][i[14]] ^
>> +		t10_dif_crc_table[0][i[15]];
>> +	}
> 
> Please indent this properly.
> 
> 		crc = t10_dif_crc_table[15][i[0] ^ (__u8)(crc >>  8)] ^
> 		      t10_dif_crc_table[14][i[1] ^ (__u8)(crc >>  0)] ^
> 		      t10_dif_crc_table[13][i[2]] ^
> 		      t10_dif_crc_table[12][i[3]] ^
> 		      t10_dif_crc_table[11][i[4]] ^
> 		      ...
> 
> - Eric
> 


View attachment "0001-T10-CRC16-function-build-time-sized-table.patch" of type "text/x-patch" (36139 bytes)