Commit d5aa3e6e authored Jan 06, 2017 by Ladi Prosek Committed by Jason Wang Jan 20, 2017

net: optimize checksum computation



Very simple loop optimization with a significant performance impact.

Microbenchmark results, modern x86-64:

buffer size | speed up
------------+---------
1500        | 1.7x
64          | 1.5x
8           | 1.15x

Microbenchmark results, POWER7:

buffer size | speed up
------------+---------
1500        | 5x
64          | 3.3x
8           | 1.13x

There is a lot of room for further improvement at the expense of
code complexity - aligned multibyte reads, LE/BE considerations,
architecture-specific optimizations, etc. This patch still keeps
things simple and readable.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

parent d4aa431f

net/checksum.c

+13 −8

Original line number	Diff line number	Diff line
		@@ -22,17 +22,22 @@

		uint32_t net_checksum_add_cont(int len, uint8_t *buf, int seq)
		{
		uint32_t sum = 0;
		uint32_t sum1 = 0, sum2 = 0;
		int i;

		for (i = seq; i < seq + len; i++) {
		if (i & 1) {
		sum += (uint32_t)buf[i - seq];
		} else {
		sum += (uint32_t)buf[i - seq] << 8;
		for (i = 0; i < len - 1; i += 2) {
		sum1 += (uint32_t)buf[i];
		sum2 += (uint32_t)buf[i + 1];
		}
		if (i < len) {
		sum1 += (uint32_t)buf[i];
		}

		if (seq & 1) {
		return sum1 + (sum2 << 8);
		} else {
		return sum2 + (sum1 << 8);
		}
		return sum;
		}

		uint16_t net_checksum_finish(uint32_t sum)