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SubjectRe: rcu_preempt running flat out on idle desktop.

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> 2013/5/8 Dave Jones <davej@redhat.com>:
> > On Wed, May 08, 2013 at 01:52:58PM -0700, Paul E. McKenney wrote:
> > > On Wed, May 08, 2013 at 04:30:42PM -0400, Dave Jones wrote:
> >
> > > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> > > > 10 root 20 0 0 0 0 S 200.0 0.0 185301:36 rcu_preempt
> > > > 553 root 20 0 268m 76m 6764 S 200.0 2.6 144579:53 Xorg
> > > > 1199 root 20 0 0 0 0 S 200.0 0.0 306:17.85 kworker/1:0
> > > > 501 root 20 0 0 0 0 S 200.0 0.0 4471:03 kworker/0:2
> > > > 12 root 20 0 0 0 0 S 200.0 0.0 67277:16 rcuop/1
> > > > 1237 davej 20 0 535m 15m 8484 S 200.0 0.5 3645:16 Terminal
> > > > 859 davej 20 0 117m 3036 1336 S 200.0 0.1 1986:55 htop
> > > >
> > > > There are a lot of processes allegedly using "200%" of CPU time, a handful
> > > > in the "196%" range, and then a bunch at 0.
> > >
> > > Yow!!! 185301 minutes is 128 days, which is a truly impressive amount of
> > > CPU time to accumulate in a few short hours.
>
> Right, Ingo has reported something about strange high numbers in top
> too. I need to investigate that.

For CPU-intense loops I have seen a small anomaly with "slightly higher
CPU usage numbers" - sometimes going to 101% or so but still converging to
around 99.9% in the long run.

The 200% bug pasted by Dave here seems to be very big and seems to affect
all tasks not just true CPU-loopers. So I'd suggest reproducing and fixing
Dave's bug first - that might fix the small anomaly I've seen.

Thanks,

Ingo


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