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[Qemu-devel] [PULL 2/6] net: optimize checksum computation
From: |
Jason Wang |
Subject: |
[Qemu-devel] [PULL 2/6] net: optimize checksum computation |
Date: |
Fri, 20 Jan 2017 11:07:46 +0800 |
From: Ladi Prosek <address@hidden>
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 <address@hidden>
Reviewed-by: Dmitry Fleytman <address@hidden>
Signed-off-by: Jason Wang <address@hidden>
---
net/checksum.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/net/checksum.c b/net/checksum.c
index 23323b0..4da72a6 100644
--- a/net/checksum.c
+++ b/net/checksum.c
@@ -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)
--
2.7.4
- [Qemu-devel] [PULL 0/6] Net patches, Jason Wang, 2017/01/19
- [Qemu-devel] [PULL 1/6] docs: Fix description of the sentence, Jason Wang, 2017/01/19
- [Qemu-devel] [PULL 2/6] net: optimize checksum computation,
Jason Wang <=
- [Qemu-devel] [PULL 3/6] m68k: QOMify the MCF Fast Ethernet Controller device, Jason Wang, 2017/01/19
- [Qemu-devel] [PULL 5/6] hw/pci: use-after-free in pci_nic_init_nofail when nic device fails to initialize, Jason Wang, 2017/01/19
- [Qemu-devel] [PULL 4/6] hw/net/dp8393x: Avoid unintentional sign extensions on addresses, Jason Wang, 2017/01/19
- [Qemu-devel] [PULL 6/6] tap: fix memory leak on failure in net_init_tap(), Jason Wang, 2017/01/19
- Re: [Qemu-devel] [PULL 0/6] Net patches, Peter Maydell, 2017/01/20