Re: [Qemu-devel] [PATCH V2 1/2] COLO-compare: Optimize tcp compare for option field

[Jason Wang]

On 2017年04月18日 10:20, Zhang Chen wrote:
> In this patch we support packet that have tcp options field.
> Add tcp options field check, If the packet have options
> field we just skip it and compare tcp payload,
> Avoid unnecessary checkpoint, optimize performance.
>
> Signed-off-by: Zhang Chen <address@hidden>
> ---
>   net/colo-compare.c | 27 ++++++++++++++++++++++++++-
>   1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/net/colo-compare.c b/net/colo-compare.c
> index aada04e..049f6f8 100644
> --- a/net/colo-compare.c
> +++ b/net/colo-compare.c
> @@ -248,7 +248,32 @@ static int colo_packet_compare_tcp(Packet *spkt, Packet 
> *ppkt)
>           spkt->ip->ip_sum = ppkt->ip->ip_sum;
>       }
>   
> -    if (ptcp->th_sum == stcp->th_sum) {
> +    /*
> +     * Check tcp header length for tcp option field.
> +     * th_off > 5 means this tcp packet have options field.
> +     * The tcp options maybe always different.
> +     * for example:
> +     * From RFC 7323.
> +     * TCP Timestamps option (TSopt):
> +     * Kind: 8
> +     *
> +     * Length: 10 bytes
> +     *
> +     *    +-------+-------+---------------------+---------------------+
> +     *    |Kind=8 |  10   |   TS Value (TSval)  |TS Echo Reply (TSecr)|
> +     *    +-------+-------+---------------------+---------------------+
> +     *       1       1              4                     4
> +     *
> +     * In this case the primary guest's timestamp always different with
> +     * the secondary guest's timestamp. COLO just focus on payload,
> +     * so we just need skip this field.h

Probably a good explanation why we can skip this kind of header. But it 
does not explain why we can skip all the rest?

Thanks

> +     */
> +    if (ptcp->th_off > 5) {
> +        ptrdiff_t tcp_offset;
> +        tcp_offset = ppkt->transport_header - (uint8_t *)ppkt->data
> +                     + (ptcp->th_off * 4);
> +        res = colo_packet_compare_common(ppkt, spkt, tcp_offset);
> +    } else if (ptcp->th_sum == stcp->th_sum) {
>           res = colo_packet_compare_common(ppkt, spkt, ETH_HLEN);
>       } else {
>           res = -1;