rcu_preempt running flat out on idle desktop.

From: Dave Jones
Date: Wed May 08 2013 - 16:30:58 EST


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.

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

Dave

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