On Wed, Mar 7, 2018 at 7:59 AM, Ilpo Järvinen <ilpo.jarvi...@helsinki.fi> wrote: > > In a non-SACK case, any non-retransmitted segment acknowledged will > set FLAG_ORIG_SACK_ACKED in tcp_clean_rtx_queue even if there is > no indication that it would have been delivered for real (the > scoreboard is not kept with TCPCB_SACKED_ACKED bits in the non-SACK > case). This causes bogus undos in ordinary RTO recoveries where > segments are lost here and there, with a few delivered segments in > between losses. A cumulative ACKs will cover retransmitted ones at > the bottom and the non-retransmitted ones following that causing > FLAG_ORIG_SACK_ACKED to be set in tcp_clean_rtx_queue and results > in a spurious FRTO undo. > > We need to make the check more strict for non-SACK case and check > that none of the cumulatively ACKed segments were retransmitted, > which would be the case for the last step of FRTO algorithm as we > sent out only new segments previously. Only then, allow FRTO undo > to proceed in non-SACK case.
Hi Ilpo - Do you have a packet trace or (even better) packetdrill script illustrating this issue? It would be nice to have a test case or at least concrete example of this. Thanks! neal
