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>
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)