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

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Message-ID: <CAFTL4hwB3XZG+C9pQ0JD4h=n_ObNH6mCBRfLW3JaxohwwRDWRA@mail.gmail.com>
Date:	Thu, 9 May 2013 23:02:08 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Dave Jones <davej@...hat.com>, paulmck@...ux.vnet.ibm.com,
	Linux Kernel <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>
Subject: Re: rcu_preempt running flat out on idle desktop.

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

I can't reproduce that issue even with the above setting. Could you
please send me your whole config?

Thanks.
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