On Thu, Jun 28, 2012 at 02:22:07PM -0400, Vlad Yasevich wrote: > On 06/28/2012 02:07 PM, Neil Horman wrote: > >On Thu, Jun 28, 2012 at 11:58:56AM -0400, Vlad Yasevich wrote: > >>On 06/28/2012 11:33 AM, Neil Horman wrote: > >>>On Wed, Jun 27, 2012 at 03:44:22PM -0400, Vlad Yasevich wrote: > >>>>On 06/27/2012 01:28 PM, Neil Horman wrote: > >>>>>On Wed, Jun 27, 2012 at 11:10:26AM -0400, Vlad Yasevich wrote: > >>>>>> > >>>>>>I didn't think of this yesterday, but I think it would be much > >>>>>>better to use pkt->transport here since you are adding the chunk to > >>>>>>the packet and it will go out on the transport of the packet. You > >>>>>>are also guaranteed that pkt->transport is set. > >>>>>> > >>>>>I don't think it really matters, as the chunk transport is used to lookup the > >>>>>packet that we append to, and if the chunk transport is unset, its somewhat > >>>>>questionable as to weather we should bundle, but if packet->transport is set, > >>>>>its probably worth it to avoid the extra conditional. > >>>>> > >>>> > >>>>Just looked at the code flow. chunk->transport may not be set until > >>>>the end of sctp_packet_append_chunk. For new data, transport may > >>>>not be set. For retransmitted data, transport is set to last > >>>>transport data was sent on. So, we could be looking at the wrong > >>>>transport. What you are trying to decided is if the current > >>>>transport we will be used can take the SACK, but you may not be > >>>>looking at the current transport. Looking at packet->transport is > >>>>the correct thing to do. > >>>> > >>>>-vlad > >>>> > >>>So, I agree after what you said above, that this is the right thing to do. That > >>>said, I just tested the change with the SCTP_RR test in netperf, and it wound up > >>>giving me horrid performance (Its reporting about 5 transactions per second). > >>>It appears that whats happening is that, because the test alternates which > >>>transports it sends out, and because it waits for a sack of teh prior packet > >>>before it sends out the next transaction, we're always missing the bundle > >>>opportunity, and always waiting for the 200ms timeout for the sack to occur. > >>>While I know this is a pessimal case, it really seems bad to me. It seems that > >>>because I was using chunk->transport previously, I luckily got the transport > >>>wrong sometimes, and it managed to bundle more often. > >>> > >>>So I'm not sure what to do here. I had really wanted to avoid adding a sysctl > >>>here, but given that this is likely a corner cases, it seems that might be the > >>>best approach. Do you have any thoughts? > >>> > >>>Neil > >>> > >> > >>that's strange. did you modify the SCTP_RR to alternate transports? > >>Seems like responses in the RR test need to go the address of the > >>sender so that we don't see things like: > >>Request (t) ---> > >> <--- Response (t2) > >> > >>Should be: > >>Request (t1) ---> > >> <--- Response (t1) > >> > >> > >>-vlad > >That would seem to me to be the case too.... > > > >However, having looked at this some more, it seems I just jumped the gun on > >this. Its happening because sctp_eat_data variants are issuing a SCTP_GEN_SACK > >command at the end of every received packet, which causes the moved_ctsn value > >to get cleared. > > Ok, that should only happen the very first time as we are supposed > to ack the first data immediately. On subsequent packets it should > just start a timer because we are following the 2pkt/200ms rule. > Then, when the response happens, we should bundle the SACK as long > as the data is leaving on the transport that moved the CTSN. > > So we might be using the wrong transport and as result you send data > and then end up waiting for a SACK. > Thats what I'm looking into now. I'll let you know when I've figured it out Neil -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
