Re: [PATCH] Performance Improvement in CRC16 Calculations.

[Douglas Gilbert]

This is a multi-part message in MIME format.
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@xxxxxxxxxxx> 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@xxxxxxxxxx]
> Sent: Friday, August 10, 2018 3:16 PM
> To: Jeffrey Lien <Jeff.Lien@xxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-crypto@xxxxxxxxxxxxxxx; linux-block@xxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx; herbert@xxxxxxxxxxxxxxxxxxx; tim.c.chen@xxxxxxxxxxxxxxx; martin.petersen@xxxxxxxxxx; David Darrington <david.darrington@xxxxxxx>; Jeff Furlong <jeff.furlong@xxxxxxx>
> 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