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SubjectRe: [PATCH] tcp: don't use timestamp from repaired skb-s to calculate RTT
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On Tue, 2014-08-12 at 13:45 +0400, Andrey Vagin wrote:
> We don't know right timestamp for repaired skb-s. Wrong RTT estimations
> isn't good, because some congestion modules heavily depends on it.
>
> This patch adds the TCPCB_REPAIRED flag, which is included in
> TCPCB_RETRANS.

...

> +
> + /* All packets are restored as if they have
> + * already been sent. skb_mstamp isn't set to
> + * avoid wrong rtt estimation.
> + */
> + if (tp->repair) {
> + TCP_SKB_CB(skb)->sacked |= TCPCB_REPAIRED;
> + TCP_SKB_CB(skb)->when = tcp_time_stamp;
> + }
> }
>
> /* Try to append data to the end of skb. */


Are you sure TCP_SKB_CB(skb)->when needs to be set ?

It should not anymore.

If yes, I believe a comment would help a lot here.

Also, please include this tag to ease stable backports (3.15+) :

Fixes: 431a91242d8d ("tcp: timestamp SYN+DATA messages")
Fixes: 740b0f1841f6 ("tcp: switch rtt estimations to usec resolution")

Thanks !




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