Re: rcu_preempt running flat out on idle desktop.

From: Paul E. McKenney
Date: Wed May 08 2013 - 16:53:23 EST


On Wed, May 08, 2013 at 04:30:42PM -0400, Dave Jones wrote:
> On what should be an idle desktop, I'm seeing really strange things.
>
> The XFCE CPU meter shows both cores are running with no idle time.
>
> here's the top of the top(1) output..
>
> 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.

> rcu_preempt is staying at the top of the list while everything else bubbles
> up the list.
>
> And what's up with those TIME entries? Box has only been up a few hours,
> so those numbers look really crazy.
>
> RCU options for this build are..
>
> CONFIG_TREE_PREEMPT_RCU=y
> CONFIG_PREEMPT_RCU=y
> CONFIG_RCU_STALL_COMMON=y
> CONFIG_RCU_USER_QS=y
> CONFIG_RCU_FANOUT=64
> CONFIG_RCU_FANOUT_LEAF=16
> # CONFIG_RCU_FANOUT_EXACT is not set
> # CONFIG_RCU_FAST_NO_HZ is not set
> CONFIG_TREE_RCU_TRACE=y
> CONFIG_RCU_BOOST=y
> CONFIG_RCU_BOOST_PRIO=1
> CONFIG_RCU_BOOST_DELAY=500
> CONFIG_RCU_NOCB_CPU=y
> CONFIG_RCU_NOCB_CPU_ALL=y
> CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
> CONFIG_PROVE_RCU=y
> # CONFIG_PROVE_RCU_REPEATEDLY is not set
> CONFIG_PROVE_RCU_DELAY=y
> CONFIG_SPARSE_RCU_POINTER=y
> # CONFIG_RCU_TORTURE_TEST is not set
> CONFIG_RCU_CPU_STALL_TIMEOUT=60
> CONFIG_RCU_CPU_STALL_VERBOSE=y
> # CONFIG_RCU_CPU_STALL_INFO is not set
> CONFIG_RCU_TRACE=y

This is 3.9, or Linus's current tree? I am guessing the latter, but
figured I should ask.

Thanx, Paul

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