linux-kernel - Re: rcu_preempt running flat out on idle desktop.

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Message-ID: <20130509092013.GA21620@gmail.com>
Date:	Thu, 9 May 2013 11:20:13 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Dave Jones <davej@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: rcu_preempt running flat out on idle desktop.


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

> 2013/5/8 Dave Jones <davej@...hat.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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