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? thanks, neal
