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

2015-07-21 Thread Yuchung Cheng 
On Fri, Jul 17, 2015 at 10:27 PM, Eric Dumazet eric.duma...@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.




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

2015-07-17 Thread Eric Dumazet 
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.



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

2015-07-17 Thread Yuchung Cheng 
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 ych...@google.com
Signed-off-by: Neal Cardwell ncardw...@google.com
---
 net/ipv4/tcp_output.c | 13 ++---
 1 file changed, 6 insertions(+), 7 deletions(-)

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
-- 
2.4.3.573.g4eafbef

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