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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>
This commit is contained in:
Ladi Prosek 2017-01-06 09:08:53 +01:00 committed by Jason Wang
parent d4aa431f94
commit d5aa3e6e0c
1 changed files with 13 additions and 8 deletions
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21
net/checksum.c
View File

@ -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)