Re: [RT] oops in 4.1.3-rt3
From: Thomas Gleixner
Date: Wed Aug 19 2015 - 16:58:55 EST
On Sun, 16 Aug 2015, Sebastian Andrzej Siewior wrote:
> * Thomas Gleixner | 2015-08-04 14:05:10 [+0200]:
>
> >On Tue, 4 Aug 2015, Nicholas Mc Guire wrote:
> >> <snip>
> >> 3 root -2 0 0 0 0 R 60.3 0.0 5756:16 ksoftirqd/0
> >> 23 root -2 0 0 0 0 R 50.8 0.0 4948:08 ksoftirqd/2
> >> 17 root -2 0 0 0 0 S 50.6 0.0 4897:13 ksoftirqd/1
> >> 29 root -2 0 0 0 0 S 50.4 0.0 4953:24 ksoftirqd/3
> >
> >So ksoftirqd eats 50+% CPU on each core. On an idle system!?! Any
> >chance that you can get a function trace snapshot out of it?
>
> This might be a .config thing, device driver or user land behaviour.
> Usually ksoftirqd should remain (almost) idle because most of BH work
> remains in task-context and not in ksoftirqd. tasklets for instance
> should run in ksoftirqd. So a function trace or event tracing to figure
> out what is scheduling the softirq might give a pointer.
> I have here a AMD box with
>
> 3 root -2 0 0 0 0 S 1.3 0.0 126:16.31 ksoftirqd/0
> 18 root -2 0 0 0 0 S 1.3 0.0 136:55.85 ksoftirqd/1
> 30 root -2 0 0 0 0 S 1.3 0.0 138:50.52 ksoftirqd/3
> 24 root -2 0 0 0 0 S 1.0 0.0 143:54.28 ksoftirqd/2
>
> with a 15 days uptime. That one percent CPU usage on a idle system looks
> odd here, too.
Not really. If ksoftirqd takes 13us per invocation and you run with
HZ=1000 then this is reasonable.
Thanks,
tglx
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