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

-----Original Message-----
From: Sergei Shtylyov [mailto:sergei.shtylyov@cogentembedded.com]
Sent: Tuesday, July 25, 2017 5:55 PM
To: maowenan; netdev@vger.kernel.org; davem@davemloft.net; weiyongjun
(A); Chenweilong
Subject: Re: [PATCH net-next] TLP: Don't reschedule PTO when there's one
outstanding TLP retransmission.

Hello!

On 7/25/2017 11:35 AM, Mao Wenan wrote:

quoted

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.

quoted

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*/

    Please add space after /* and before */

Ok, thank you.

quoted

+		if (tp->tlp_high_seq) {
+			return false;
+		}

    {} not needed.

Ok, I will send the V2.

[...]

MBR, Sergei