On Tue, Aug 12, 2014 at 05:15:01AM -0700, Eric Dumazet wrote:
> 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's used in tcp_rearm_rto() for calculating a retransmit timeout.
...
const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
...
"when" is used as a start point, so I think it's acceptable here.
I will add a comment. Thanks.
>
> 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,
Andrew
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