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Re: [Qemu-devel] [PATCH] net: optimize checksum computation
From: |
Dmitry Fleytman |
Subject: |
Re: [Qemu-devel] [PATCH] net: optimize checksum computation |
Date: |
Sun, 8 Jan 2017 11:03:12 +0200 |
> On 6 Jan 2017, at 10:08 AM, Ladi Prosek <address@hidden> 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 <address@hidden>
>
> Signed-off-by: Ladi Prosek <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
>