Benoit PAPILLAULT wrote: > I did a similar test here and results is very strange. AP was my good > old linksys WRT54G running an iperf server. Client was a laptop running > either ath5k or madwifi/trunk and an iperf client. Channel is 5. Both > drivers show the same behaviour. > > At the beginning, throughput was very low : 500 - 600 kbit/s. Suddenly > (after few minutes), it jumps to 15 - 17 Mbit/s and then few minutes > later (let's say 10 - 20 minutes maybe), it jumps back to 500 - 600 > kbit/s. Using a fixed rate has no effect. > > I used my latest wireless monitoring tools and I did not saw lost of > duplicates or lost packets. The only difference was the number of > packets sent by seconds.... > > Looking a my syslog, I just saw few messages, unrelated in time with the > throughput going up or down. They were: > - ath5k : unsupported jumbo > - switching to short barker preamble > - switching to long barker preamble > > I can repeat the same test with iwl3945 as well, if needed. While reading the code for calculating the frame duration, i noticed something odd: It doesn't seem to be taking into account the short vs long preamble distinction for ERP rates. IMHO this might be causing issues like this. I've seen similar behaviour a long time ago when testing iwl3945 against a Broadcom AP with exactly the same throughput drop (500- 600 kbits/s). When I analyzed the problem with an extra monitor mode card, I found out that the throughput drop is caused by a huge number of retransmissions, and if I remember correctly (I didn't look for this specifically back then), the retransmissions went down the rate scaling table until they hit the first non-ERP rate and that one worked on the first try. Johannes, does that sound like a probable cause? If so, it should be easy to fix. - Felix -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
