Re: [PATCH] Performance Improvement in CRC16 Calculations.

[Christophe LEROY]

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 Ã 16:22, Douglas Gilbert a ÃcritÂ:
> 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.ÂÂ 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:ÂÂÂÂÂÂÂ bw=201.5 MiB/s
> > > BE Modified CRC Calc:Â bw=968.1 MiB/s
> > > 4.80x performance improvement
> > >
> > > LE Base Kernel:ÂÂÂÂÂÂÂ bw=357 MiB/s
> > > LE Modified CRC Calc:Â bw=1964 MiB/s
> > > 5.51x performance improvement
> > >
> > > FIO Sequential Read, 64K Block Size, Queue Depth 64
> > > BE Base Kernel:ÂÂÂÂÂÂÂ bw=611.2 MiB/s
> > > BE Modified CRC calc:Â bw=684.9 MiB/s
> > > 1.12x performance improvement
> > >
> > > LE Base Kernel:ÂÂÂÂÂÂÂ bw=797 MiB/s
> > > LE Modified CRC Calc:Â 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).
> >
> > > Â __u16 crc_t10dif_generic(__u16 crc, const unsigned char *buffer,
> > > size_t len)Â {
> > > -ÂÂÂ unsigned int i;
> > > +ÂÂÂ const __u8 *i = (const __u8 *)buffer;
> > > +ÂÂÂ const __u8 *i_end = i + len;
> > > +ÂÂÂ const __u8 *i_last16 = i + (len / 16 * 16);
> >
> > 'i' is normally a loop counter, not a pointer.
> > Use 'p', 'p_end', and 'p_last16'.
> >
> > > -ÂÂÂ for (i = 0 ; i < len ; i++)
> > > -ÂÂÂÂÂÂÂ crc = (crc << 8) ^ t10_dif_crc_table[((crc >> 8) ^ 
> > > buffer[i]) & 0xff];
> > > +ÂÂÂ for (; i < i_last16; i += 16) {
> > > +ÂÂÂÂÂÂÂ crc = t10_dif_crc_table[15][i[0] ^ (__u8)(crc >>Â 8)] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[14][i[1] ^ (__u8)(crc >>Â 0)] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[13][i[2]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[12][i[3]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[11][i[4]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[10][i[5]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[9][i[6]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[8][i[7]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[7][i[8]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[6][i[9]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[5][i[10]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[4][i[11]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[3][i[12]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[2][i[13]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[1][i[14]] ^
> > > +ÂÂÂÂÂÂÂ t10_dif_crc_table[0][i[15]];
> > > +ÂÂÂ }
> >
> > Please indent this properly.
> >
> > ÂÂÂÂÂÂÂ crc = t10_dif_crc_table[15][i[0] ^ (__u8)(crc >>Â 8)] ^
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ t10_dif_crc_table[14][i[1] ^ (__u8)(crc >>Â 0)] ^
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ t10_dif_crc_table[13][i[2]] ^
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ t10_dif_crc_table[12][i[3]] ^
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ t10_dif_crc_table[11][i[4]] ^
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ ...
> >
> > - Eric