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Date: Thu, 16 Aug 2018 17:41:13 +0200
From: Christophe LEROY <christophe.leroy@....fr>
To: dgilbert@...erlog.com, 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,
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@...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
>>
>
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