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. We follow the sack every other packet rule instead of taking the opportunity to bundle on send, so we're sending a packet with a sack, and a second packet with a 1 byte data chunk (thats part of the SCTP_RR test). I'm not sure why I didn't see this when I was using the chunk->transport pointer. Maybe I was just getting lucky with timing... I'll see how I can go about fixing this. Neil > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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
