Today Salman Zafar and I observed something that we hadn't noticed before (not sure if it didn't happen, or we didn't notice it) -- the PandaBoards in the build farm have high latency, with occasional packet drops, when pinged at 1-second intervals (the default for the 'ping' command). Oddly, when flood-pinged, they don't drop any packets, and the latency improves. This sounds a lot like the storage performance bug, without the storage :-) Perhaps an IRQ is being missed, and a subsequent IRQ (or polling event or something else) is causing the driver to pick up the data late? (Just speculating) Regular ping ... ------------------------------------------- $ ping -c20 5-1 PING cdot-panda-5-1 (192.168.1.151) 56(84) bytes of data. 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=1 ttl=64 time=0.753 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=2 ttl=64 time=49.8 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=3 ttl=64 time=128 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=4 ttl=64 time=8.21 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=5 ttl=64 time=233 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=6 ttl=64 time=646 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=7 ttl=64 time=0.609 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=8 ttl=64 time=248 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=9 ttl=64 time=318 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=10 ttl=64 time=267 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=11 ttl=64 time=267 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=12 ttl=64 time=268 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=13 ttl=64 time=266 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=14 ttl=64 time=265 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=15 ttl=64 time=153 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=16 ttl=64 time=0.632 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=17 ttl=64 time=61.6 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=18 ttl=64 time=0.628 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=19 ttl=64 time=75.9 ms 64 bytes from cdot-panda-5-1 (192.168.1.151): icmp_req=20 ttl=64 time=23.6 ms --- cdot-panda-5-1 ping statistics --- 20 packets transmitted, 20 received, 0% packet loss, time 19021ms rtt min/avg/max/mdev = 0.609/164.416/646.835/159.032 ms ------------------------------------------- Notice the 164 mS average latency. No packet loss in this particular sample, though. Now a flood ping: ------------------------------------------- # ping -f -c20 5-1 PING cdot-panda-5-1 (192.168.1.151) 56(84) bytes of data. --- cdot-panda-5-1 ping statistics --- 20 packets transmitted, 20 received, 0% packet loss, time 92ms rtt min/avg/max/mdev = 0.373/4.666/19.813/6.597 ms, pipe 2, ipg/ewma 4.883/3.134 ms ------------------------------------------- Results vary but are generally repeatable. This kernel (which is a 2.6.35.3) doesn't appear to be built with the appropriate /sys/kernel/debug/usbmon bits for tracing with tcpdump. (Anyone know offhand the kernel flags for that?) -Chris _______________________________________________ arm mailing list arm@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/arm
