diff mbox

[net-next,1/2] tcp: don't extend RTO on failed loss probe attempts

Message ID 1437168172-24201-2-git-send-email-ycheng@google.com
State Changes Requested, archived
Delegated to: David Miller
Headers show

Commit Message

Yuchung Cheng July 17, 2015, 9:22 p.m. UTC 
If TLP was unable to send a probe, it extended the RTO to
now + icsk_rto. But extending the RTO makes little sense
if no TLP probe went out. With this commit, instead of
extending the RTO we re-arm it relative to the transmit time
of the write queue head.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
---
 net/ipv4/tcp_output.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

Comments

Eric Dumazet July 18, 2015, 5:27 a.m. UTC | #1 
On Fri, 2015-07-17 at 14:22 -0700, Yuchung Cheng wrote:
> If TLP was unable to send a probe, it extended the RTO to
> now + icsk_rto. But extending the RTO makes little sense
> if no TLP probe went out. With this commit, instead of
> extending the RTO we re-arm it relative to the transmit time
> of the write queue head.

But what was the reason the probe could not be sent ?

If it is local congestion or memory allocation error, it does make sense
to not add fuel to the fire.



--
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
Yuchung Cheng July 21, 2015, 5:55 p.m. UTC | #2 
On Fri, Jul 17, 2015 at 10:27 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
> On Fri, 2015-07-17 at 14:22 -0700, Yuchung Cheng wrote:
> > If TLP was unable to send a probe, it extended the RTO to
> > now + icsk_rto. But extending the RTO makes little sense
> > if no TLP probe went out. With this commit, instead of
> > extending the RTO we re-arm it relative to the transmit time
> > of the write queue head.
>
> But what was the reason the probe could not be sent ?
>
> If it is local congestion or memory allocation error, it does make sense
> to not add fuel to the fire.
Good point. We can identify those so we don't attempt to
retransmit on these errors, but will retransmit on receive-window
limit. I'll re-spin the patch.

>
>
>
--
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 mbox

Patch

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7105784..deb944b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2275,13 +2275,12 @@  void tcp_send_loss_probe(struct sock *sk)
 		tp->tlp_high_seq = tp->snd_nxt;
 
 rearm_timer:
-	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-				  inet_csk(sk)->icsk_rto,
-				  TCP_RTO_MAX);
-
-	if (likely(!err))
-		NET_INC_STATS_BH(sock_net(sk),
-				 LINUX_MIB_TCPLOSSPROBES);
+	if (likely(!err)) {
+		/* Reset s.t. tcp_rearm_rto will restart timer from now */
+		inet_csk(sk)->icsk_pending = 0;
+		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
+	}
+	tcp_rearm_rto(sk);
 }
 
 /* Push out any pending frames which were held back due to