* [Qemu-devel] [PATCH] net: optimize checksum computation
@ 2017-01-06 8:08 Ladi Prosek
2017-01-08 9:03 ` Dmitry Fleytman
0 siblings, 1 reply; 3+ messages in thread
From: Ladi Prosek @ 2017-01-06 8:08 UTC (permalink / raw)
To: qemu-devel; +Cc: jasowang, dmitry
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>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [Qemu-devel] [PATCH] net: optimize checksum computation
2017-01-06 8:08 [Qemu-devel] [PATCH] net: optimize checksum computation Ladi Prosek
@ 2017-01-08 9:03 ` Dmitry Fleytman
2017-01-09 3:32 ` Jason Wang
0 siblings, 1 reply; 3+ messages in thread
From: Dmitry Fleytman @ 2017-01-08 9:03 UTC (permalink / raw)
To: Ladi Prosek; +Cc: qemu-devel, jasowang
> On 6 Jan 2017, at 10:08 AM, Ladi Prosek <lprosek@redhat.com> wrote:
>
> 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.
Reviewed-by: Dmitry Fleytman <dmitry@daynix.com>
>
> Signed-off-by: Ladi Prosek <lprosek@redhat.com>
> ---
> 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
>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [Qemu-devel] [PATCH] net: optimize checksum computation
2017-01-08 9:03 ` Dmitry Fleytman
@ 2017-01-09 3:32 ` Jason Wang
0 siblings, 0 replies; 3+ messages in thread
From: Jason Wang @ 2017-01-09 3:32 UTC (permalink / raw)
To: Dmitry Fleytman, Ladi Prosek; +Cc: qemu-devel
On 2017年01月08日 17:03, Dmitry Fleytman wrote:
>> On 6 Jan 2017, at 10:08 AM, Ladi Prosek <lprosek@redhat.com> wrote:
>>
>> 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.
> Reviewed-by: Dmitry Fleytman <dmitry@daynix.com>
>
Applied to -net.
Thanks
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-01-08 9:03 ` Dmitry Fleytman
2017-01-09 3:32 ` Jason Wang
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