RE: [PATCH] Performance Improvement in CRC16 Calculations.

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 <redacted>
Reviewed-by: Jeff Furlong <redacted>
Signed-off-by: Jeff Lien <redacted>
---
 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]];