From: David Laight Subject: RE: [PATCH] Performance Improvement in CRC16 Calculations. Date: Mon, 13 Aug 2018 11:45:21 +0000 Message-ID: <8508c92d70dc41ffb66557e13c988dca@AcuMS.aculab.com> References: <1533928331-21303-1-git-send-email-jeff.lien@wdc.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Cc: "herbert@gondor.apana.org.au" , "tim.c.chen@linux.intel.com" , "martin.petersen@oracle.com" , "david.darrington@wdc.com" , "jeff.furlong@wdc.com" To: 'Jeff Lien' , "linux-kernel@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" Return-path: In-Reply-To: <1533928331-21303-1-git-send-email-jeff.lien@wdc.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org From: Jeff Lien > Sent: 10 August 2018 20:12 > > 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 > > Reviewed-by: Dave Darrington > Reviewed-by: Jeff Furlong > Signed-off-by: Jeff Lien > --- > crypto/crct10dif_common.c | 605 +++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 569 insertions(+), 36 deletions(-) > > diff --git a/crypto/crct10dif_common.c b/crypto/crct10dif_common.c > index b2fab36..40e1d6c 100644 > --- a/crypto/crct10dif_common.c > +++ b/crypto/crct10dif_common.c > @@ -32,47 +32,580 @@ > * x^16 + x^15 + x^11 + x^9 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 > * gt: 0x8bb7 > */ > -static const __u16 t10_dif_crc_table[256] = { ... > + } > }; > > __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); > > - 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]]; ... I suspect that all the gain comes from a slight relaxation of the register dependency chain and the loop unrolling. A more interesting version would be to generate the lookup table for a byte followed by 3 zero bytes. You could then run four separate register dependency chains using the same 256 entry lookup table. A little bit of work at the end of the buffer should sort it all out. There is also the lookup table free version: uint32_t crc_step(uint32_t crc, uint32_t byte_val) { uint32_t t = crc ^ (byte_val & 0xff); t = (t ^ t << 4) & 0xff; return crc >> 8 ^ t << 8 ^ t << 3 ^ t >> 4; } David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)