Re: [PATCH] Performance Improvement in CRC16 Calculations.

[Christophe LEROY <christophe.leroy@c-s.fr>]

Hi,

Please include your new patch as plain text inside the mail, not as a 
MIME attachment. Otherwise it is not downloadable from 
https://patchwork.kernel.org/patch/10563093/

Christophe

Le 16/08/2018 à 16:22, Douglas Gilbert a écrit :
> 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@perches.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@kernel.org]
>> Sent: Friday, August 10, 2018 3:16 PM
>> To: Jeffrey Lien <Jeff.Lien@wdc.com>
>> Cc: linux-kernel@vger.kernel.org; linux-crypto@vger.kernel.org; 
>> linux-block@vger.kernel.org; linux-scsi@vger.kernel.org; 
>> herbert@gondor.apana.org.au; tim.c.chen@linux.intel.com; 
>> martin.petersen@oracle.com; David Darrington 
>> <david.darrington@wdc.com>; Jeff Furlong <jeff.furlong@wdc.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
>>
>