ksoftirqd 100% cpu usage, even with low network load
|Reported by:||kubuntu@…||Owned by:||developers|
I have openwrt on a fonera, with the network set up as follows:
internet <<wireless eap-ttls/pap>> (ath1)[fonera](eth0) <<wired switched lan>> [pc's]
When uploading from a pc on the lan to the internet, for example when using bittorrent, ksoftirqd on the fonera often (but not always) starts using all available cpu (as if in an infinite loop), and as a result the whole thing becomes very slow. This happens at rather low network throughput of around 80-100kB/s, and with only a dozen or so bt-clients connected. Stopping or artificially speed-limiting the upload network traffic (on the pc) to speeds lower than about 60kB/s causes the cpu usage of ksoftirqd to go down abruptly from ~100% to absolutely nothing.
This situation of high cpu usage may last anywhere from a few minutes to many hours, and sometimes does not happen at all or only intermittently. In such cases, upload speeds via the wireless connection can reach beyond 1MB/s without any problem; ksoftirqd cpu usage stays at or very near zero all the way in these cases.
I have yet to see this problem when downloading, it seems to happen only when uploading.
In top, ksoftirqd is of course high up in the list of processes...
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3 root 15 -5 0 0 0 R 95.4 0.0 469:01.54 [ksoftirqd/0]
contents of /proc/interrupts:
CPU0 2: 0 MIPS cascade 3: 786695001 MIPS wifi0 4: 21627235 MIPS eth0 7: 86358251 MIPS timer 34: 0 AR5315 misc ar5315_ahb_proc_interrupt 36: 0 AR5315 misc cascade 37: 8 AR5315 misc serial 54: 0 AR5315 GPIO ar531x_reset ERR: 0
dmesg and the log show nothing out of the ordinary, apart from an occasional cryptic "wifi0: stuck beacon; resetting (bmiss count 11)" which, based on the times this occures, isn't related.
Apparently I am not the only one seeing something like this, see the comment by "chimera" at http://forum.openwrt.org/viewtopic.php?id=8904 reporting similar symptoms.
openwrt (svn 9442) on a fonera, kernel 126.96.36.199-atheros-1
Linux fonera 188.8.131.52 #1 Thu Oct 25 13:22:23 CEST 2007 mips unknown