On Tue, Jul 25, 2017 at 7:12 PM, maowenan <maowe...@huawei.com> wrote: > > > > > -----Original Message----- > > From: Neal Cardwell [mailto:ncardw...@google.com] > > Sent: Tuesday, July 25, 2017 9:30 PM > > To: maowenan > > Cc: Netdev; David Miller; weiyongjun (A); Chenweilong; Yuchung Cheng; > > Nandita Dukkipati > > Subject: Re: [PATCH net-next] TLP: Don't reschedule PTO when there's one > > outstanding TLP retransmission. > > > > On Tue, Jul 25, 2017 at 4:35 AM, Mao Wenan <maowe...@huawei.com> > > wrote: > > > 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 <maowe...@huawei.com> > > > > Thanks for posting this. This is a pretty involved scenario. To help > > document/test precisely what the behavior is before and after your patch, > > would you be able to post a packetdrill ( > > https://github.com/google/packetdrill ) > > test case for this scenario? > > > > Can I ask if you saw this scenario in an actual trace, or noticed this by > > inspection? > [Mao Wenan] It is my actual product scenario, from some debug trace info > I found that PTO is always rescheduled before RTO, this is PTO is trigged > by receiving one tcp_ack packets. After this patch, the product works well and > there is no previous issue happen. The packet can retransmit with RTO if TLP > probe > is lost. > I will say sorry that my local test can't reproduce because i can't build > successfully the same > complex scenario, I don't have mature test case to reproduce now but I will > do my best to try > in local test environment. tcpdump output of an example trace also helps. Feel free to remove IP address, ports, or payload information. We only need the timing and TCP header info.
> Thank you. > > > > thanks, > > neal
