| Message ID | CAH4NVoT4ofCNKAmcnO1AgEbs+ywbXom=E28k2VU4dB+yK79S_A@mail.gmail.com |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 2014-03-12 at 21:46 +0800, Yong Zhang wrote: > hi， > > I am trying to to apply patch 9ad7c049f0f79c418e293b1b68cf10d68f54fcdb > to my old version kernel, but I am not understanding the following > changes. > > The comments int the patch say ssthresh may reduce unnecessarily > druing 3WHS, but i can not find the reduce operation of ssthresh > during 3WHS. > > Can you please explain when dose this may hanppen? > You might CC patch author when asking such questions... > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index bef9f04..ea0d218 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -880,6 +880,11 @@ static void tcp_init_metrics(struct sock *sk) > > tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); > if (tp->snd_ssthresh > tp->snd_cwnd_clamp) > tp->snd_ssthresh = tp->snd_cwnd_clamp; > + } else { > + /* ssthresh may have been reduced unnecessarily during. > + * 3WHS. Restore it back to its initial default. > + */ > + tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; > } > > > Thanks, > Fel > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Mar 12, 2014 at 7:26 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > > On Wed, 2014-03-12 at 21:46 +0800, Yong Zhang wrote: > > hi， > > > > I am trying to to apply patch 9ad7c049f0f79c418e293b1b68cf10d68f54fcdb > > to my old version kernel, but I am not understanding the following > > changes. > > > > The comments int the patch say ssthresh may reduce unnecessarily > > druing 3WHS, but i can not find the reduce operation of ssthresh > > during 3WHS. > > > > Can you please explain when dose this may hanppen? I can think of two cases: 1. active open: syn -> (timeout) -> tcp_retransmit_timer -> tcp_enter_loss -> reduce ssthresh 2. passive fast open: data sent during 3whs after syn-ack -> timeout -> tcp_enter_loss -> reduce ssthresh It's arguable the resetting is necessary or not. but resetting ssthresh seems better b/c it is unlikely to be the BDP, especially in case 1. btw, it'll be easy to test this using https://code.google.com/p/packetdrill/ > > > > You might CC patch author when asking such questions... > > > > > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > > index bef9f04..ea0d218 100644 > > --- a/net/ipv4/tcp_input.c > > +++ b/net/ipv4/tcp_input.c > > @@ -880,6 +880,11 @@ static void tcp_init_metrics(struct sock *sk) > > > > tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); > > if (tp->snd_ssthresh > tp->snd_cwnd_clamp) > > tp->snd_ssthresh = tp->snd_cwnd_clamp; > > + } else { > > + /* ssthresh may have been reduced unnecessarily during. > > + * 3WHS. Restore it back to its initial default. > > + */ > > + tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; > > } > > > > > > Thanks, > > Fel > > -- > > To unsubscribe from this list: send the line "unsubscribe netdev" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index bef9f04..ea0d218 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -880,6 +880,11 @@ static void tcp_init_metrics(struct sock *sk) tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); if (tp->snd_ssthresh > tp->snd_cwnd_clamp) tp->snd_ssthresh = tp->snd_cwnd_clamp; + } else { + /* ssthresh may have been reduced unnecessarily during. + * 3WHS. Restore it back to its initial default. + */ + tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; }