On Wed, May 4, 2011 at 4:42 PM, Daniel Halperin <dhalperi@xxxxxxxxxxxxxxxxx> wrote: > Hi, > > I have two identical Dell Inspiron 530n desktops running latest w-t > (07e789c5094735747b3df8a7840f61467575ba9e, master 2011-05-04) on > Ubuntu 10.04.2 LTS. I have uninstalled network-manager from both > devices and, as far as I can tell, no software processes or daemons > interfere with my wireless configurations. > > The AP machine has an AR9280-based device and an IWL5300 based device. > I blacklist ath9k and iwlagn modules from loading on boot. It is > running latest hostap.git, though I've seen the same issue with older > versions. > > The client machine has one AR9380-based NIC, one IWL5300-based NIC, > and one RT2800pci NIC. I blacklist ath9k, iwlagn, and rt2800pci from > loading on boot. > > When I set up the client to connect (using iwconfig essid) to the AP > (no encryption, channel 48 with HT40-) and run iperf, I sometimes see > 2-second drops of the connection. I run iperf to generate elastic TCP > flows that see ~150 Mbps, and in parallel I run ping <AP> -i 0.2. > Here's the ping log: > > 64 bytes from 192.168.1.2: icmp_seq=622 ttl=64 time=107 ms > 64 bytes from 192.168.1.2: icmp_seq=623 ttl=64 time=117 ms > 64 bytes from 192.168.1.2: icmp_seq=624 ttl=64 time=125 ms > 64 bytes from 192.168.1.2: icmp_seq=625 ttl=64 time=2152 ms > 64 bytes from 192.168.1.2: icmp_seq=626 ttl=64 time=1989 ms > 64 bytes from 192.168.1.2: icmp_seq=627 ttl=64 time=1779 ms > 64 bytes from 192.168.1.2: icmp_seq=628 ttl=64 time=1570 ms > 64 bytes from 192.168.1.2: icmp_seq=629 ttl=64 time=1360 ms > 64 bytes from 192.168.1.2: icmp_seq=630 ttl=64 time=1150 ms > 64 bytes from 192.168.1.2: icmp_seq=631 ttl=64 time=950 ms > 64 bytes from 192.168.1.2: icmp_seq=632 ttl=64 time=750 ms > 64 bytes from 192.168.1.2: icmp_seq=633 ttl=64 time=550 ms > 64 bytes from 192.168.1.2: icmp_seq=634 ttl=64 time=340 ms > 64 bytes from 192.168.1.2: icmp_seq=635 ttl=64 time=130 ms > 64 bytes from 192.168.1.2: icmp_seq=636 ttl=64 time=2.73 ms > 64 bytes from 192.168.1.2: icmp_seq=637 ttl=64 time=1.18 ms > 64 bytes from 192.168.1.2: icmp_seq=638 ttl=64 time=1.18 ms > 64 bytes from 192.168.1.2: icmp_seq=639 ttl=64 time=1.18 ms > 64 bytes from 192.168.1.2: icmp_seq=640 ttl=64 time=1.18 ms > > you can see that ping times are large while the TCP flow is active, > but drop to about 1.18ms after it stops. You can also clearly see the > pings get backed-up for 2 seconds and then release. This tends to > happen in the last 5 seconds of a 30s TCP flow, which starts almost > immediately after association. I wonder if it might be related to some > event that may get triggered 30s after association in either hostap or > mac80211 or ath9k. > > This is reproducible (albeit infrequently) with the stock w-t kernel; > I've also generated a version of the code in which I print out > messages (KERN_INFO priority) inside of minstrel_ht whenever get_rate > is called and whenever tx_status is called. I verified that there is > **NO LOSS** measured by either side. Also, the gap in the messages is > nearly exactly 2 seconds long, e.g., 2.03 seconds. > > Any thoughts as to what could be causing this? > > A final, but probably wrong, note. This seems to be (qualitatively) > harder to reproduce if I don't compile in rt2800pci support. But, I > blacklist the modules and I've verified that none of them are loaded > on boot, so I don't know why this would be a problem. I seem to have found a better way to make it reproducible: Once it triggers once, if I run: ifconfig wlan1 down ifconfig wlan1 up 192.168.1.11 iwconfig wlan1 essid csitool iperf -c 192.168.1.2 -i1 it will trigger again. Here's a representative iperf log: iperf -c 192.168.1.2 -i1 -t 33 ------------------------------------------------------------ Client connecting to 192.168.1.2, TCP port 5001 TCP window size: 16.0 KByte (default) ------------------------------------------------------------ [ 3] local 192.168.1.11 port 54479 connected with 192.168.1.2 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0- 1.0 sec 13.3 MBytes 111 Mbits/sec [ 3] 1.0- 2.0 sec 18.0 MBytes 151 Mbits/sec [ 3] 2.0- 3.0 sec 16.3 MBytes 137 Mbits/sec [ 3] 3.0- 4.0 sec 15.0 MBytes 126 Mbits/sec [ 3] 4.0- 5.0 sec 15.6 MBytes 131 Mbits/sec [ 3] 5.0- 6.0 sec 14.9 MBytes 125 Mbits/sec [ 3] 6.0- 7.0 sec 13.4 MBytes 112 Mbits/sec [ 3] 7.0- 8.0 sec 15.7 MBytes 132 Mbits/sec [ 3] 8.0- 9.0 sec 15.7 MBytes 131 Mbits/sec [ 3] 9.0-10.0 sec 16.2 MBytes 136 Mbits/sec [ 3] 10.0-11.0 sec 17.6 MBytes 148 Mbits/sec [ 3] 11.0-12.0 sec 16.8 MBytes 141 Mbits/sec [ 3] 12.0-13.0 sec 16.8 MBytes 141 Mbits/sec [ 3] 13.0-14.0 sec 17.6 MBytes 148 Mbits/sec [ 3] 14.0-15.0 sec 10.8 MBytes 90.7 Mbits/sec [ 3] 15.0-16.0 sec 15.8 MBytes 133 Mbits/sec [ 3] 16.0-17.0 sec 16.0 MBytes 134 Mbits/sec [ 3] 17.0-18.0 sec 16.7 MBytes 140 Mbits/sec [ 3] 18.0-19.0 sec 14.7 MBytes 123 Mbits/sec [ 3] 19.0-20.0 sec 15.8 MBytes 133 Mbits/sec [ 3] 20.0-21.0 sec 16.0 MBytes 134 Mbits/sec [ 3] 21.0-22.0 sec 14.9 MBytes 125 Mbits/sec [ 3] 22.0-23.0 sec 15.7 MBytes 132 Mbits/sec [ 3] 23.0-24.0 sec 15.2 MBytes 127 Mbits/sec [ 3] 24.0-25.0 sec 13.9 MBytes 117 Mbits/sec [ 3] 25.0-26.0 sec 14.1 MBytes 118 Mbits/sec [ 3] 26.0-27.0 sec 16.4 MBytes 137 Mbits/sec [ 3] 27.0-28.0 sec 15.0 MBytes 126 Mbits/sec [ 3] 28.0-29.0 sec 9.70 MBytes 81.4 Mbits/sec [ 3] 29.0-30.0 sec 0.00 Bytes 0.00 bits/sec [ 3] 30.0-31.0 sec 1.68 MBytes 14.1 Mbits/sec [ 3] 31.0-32.0 sec 10.2 MBytes 85.7 Mbits/sec [ 3] 32.0-33.0 sec 11.1 MBytes 93.5 Mbits/sec [ 3] 0.0-33.0 sec 467 MBytes 118 Mbits/sec -- 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
