RE: [PATCH net-next] TLP: Don't reschedule PTO when there's one outstanding TLP retransmission.

-----Original Message-----
From: netdev-owner@vger.kernel.org [mailto:netdev-owner@vger.kernel.org]
On Behalf Of Mao Wenan
Sent: Tuesday, July 25, 2017 4:36 PM
To: netdev@vger.kernel.org; davem@davemloft.net; weiyongjun (A);
Chenweilong
Subject: [PATCH net-next] TLP: Don't reschedule PTO when there's one
outstanding TLP retransmission.

If there is one TLP probe went out(TLP use the write_queue_tail packet as TLP
probe, we assume this first TLP probe named A), and this TLP probe was not
acked by receive side.

Then the transmit side sent the next two packetes out(named B,C), but
unfortunately these two packets are also not acked by receive side.

And then there is one data packet with ack_seq A arrive, in tcp_ack() will call
tcp_schedule_loss_probe() to rearm PTO, the handler
tcp_send_loss_probe() pass if(tp->tlp_high_seq)(because there is one
outstanding TLP named A,tp->tlp_high_seq is not zero), so the new TLP probe
can't be went out and need to rearm the RTO timer(timeout is relative to the
transmit time of the write queue head).

After this, another data packet with ack_seq A is received, if the
tlp_time_stamp is after rto_time_stamp, it will reset the TLP timeout with
delta value, which is before previous RTO timeout, so PTO is rearm and
previous RTO is cleared. This TLP probe also can't be sent out because of
tp->tlp_high_seq != 0, so there is no way(or need very long time)to retransmit
the packet because of TLP A is lost.

This fix is not to pass the if(tp->tlp_high_seq) in tcp_schedule_loss_probe()
when TLP PTO is after RTO, It is no need to reschedule PTO when there is one
outstanding TLP retransmission, so if the TLP A is lost then RTO can retransmit
that packet, and tp->tlp_high_seq will be set to 0. After this TLP will go to the
normal work process.

Signed-off-by: Mao Wenan <redacted>
---
 net/ipv4/tcp_output.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index

886d874..0c8da1c 100644

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c

@@ -2423,6 +2423,10 @@ bool tcp_schedule_loss_probe(struct sock *sk)
 	tlp_time_stamp = tcp_jiffies32 + timeout;
 	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
 	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
+		/*It is no need to reschedule PTO when there is one outstanding TLP

retransmission*/
+		if (tp->tlp_high_seq) {
+			return false;
+		}
 		s32 delta = rto_time_stamp - tcp_jiffies32;
 		if (delta > 0)
 			timeout = delta;
--
2.5.0