#20618: sysrq-trigger: missing 'l' (small letter L) command key
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Reporter: braveheart_leo@… | Owner: developers
Type: defect | Status: new
Priority: normal | Milestone: Chaos Calmer (trunk)
Component: kernel | Version: Trunk
Keywords: |
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Hi,
I'm running a custom-compiled `DESIGNATED DRIVER (Bleeding Edge, r47055)`
on WZR-HP-AG300H.
I'm trying to investigate a possible issue I'm experiencing in which I
notice a constant 20% CPU usage from the `kworker/u2:2` kernel thread at
certain times whenever wireless clients are connected.
`dmesg` and `logread` output no messages that could give a hint as to why
this is happening. Dumping a "stack backtrace for all active CPUs" [1] via
`echo l >/proc/sysrq-trigger` results in
{{{
sysrq: SysRq : HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-
tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j)
show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p)
show-all-timers(q) sync(s) show-task-states(t) unmount(u) show-blocked-
tasks(w)
}}}
I'm trying to determine whether there exists a bug in the kernel, or in
this case in its wireless subsystem (mac80211?, ath9k?), as outlined in
[2]. Unfortunately, I'm not able to proceed because the 'l' command does
not exist for `/proc/sysrq-trigger`.
I haven't changed anything in the default kernel config for ar71xx target,
so I was wondering how I can get a stack backtrace via sysrq-trigger. Is
there any kernel config I can turn ON for this? Perhaps this (strack
tracing?) was turned off because it impacts performance, even kernel size
maybe?
Regarding the 20% CPU usage from one of the kernel threads when wireless
clients are connected, are there other ways I could try to debug this
issue to find out more info?
I haven't isolated the conditions that trigger this CPU hog. There are
times that wireless clients are connected but I don't see `kworker/u2:2`
using up 20% of the CPU all the time. Perhaps you could give me a hint as
to why this might be happening?
[1] https://www.kernel.org/doc/Documentation/sysrq.txt
[2] http://askubuntu.com/questions/33640/kworker-what-is-it-and-why-is-it-
hogging-so-much-cpu
--
Ticket URL: <https://dev.openwrt.org/ticket/20618>
OpenWrt <http://openwrt.org>
Opensource Wireless Router Technology
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