linux-kernel - [next-20120823] NOHZ: local_softirq

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Date:	Thu, 23 Aug 2012 12:04:44 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Paul McKenney <paul.mckenney@...aro.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-next <linux-next@...r.kernel.org>
Subject: [next-20120823] NOHZ: local_softirq_pending 200 on s/r

Hi,

this week I was seeing the below NOHZ messages in my logs especially
when suspending and resuming.

Currently, I am using linux-next (next-20120823) on Ubuntu/precise
AMD64 with a Intel S(a)N(dy)B(ridge)-CPU.

$ dmesg | grep -A1 -B1 -i nohz
[  720.331819] Disabling non-boot CPUs ...
[  720.332035] NOHZ: local_softirq_pending 200
[  720.434312] smpboot: CPU 1 is now offline
[  720.434825] NOHZ: local_softirq_pending 200
[  720.538237] smpboot: CPU 2 is now offline
[  720.538676] NOHZ: local_softirq_pending 200
[  720.642162] smpboot: CPU 3 is now offline

If I manually disable the cpuX... First I did not see NOHZ messages
but then there were some lines seen especially when cpuX went offline
(here: cpu1)

# echo 0 >/sys/devices/system/cpu/cpu1/online

[ dmeg ]
[ 2605.515771] smpboot: CPU 1 is now offline

The same with cpu2 and cpu3.

Jack Winter confirmed to see similiar NOHZ messages also on
v3.4.9-rt17 kernel (CPU: Core2Duo when no suspend performed):

[15223.171585] NOHZ: local_softirq_pending 08

So, the issue is seen on linux-next and -rt kernels.

According to Thomas "softirq 0x200 is the RCU one" and he requested me
to address the issue to Paul on #linux-rt.

Regards,
- Sedat -

View attachment "dmesg_3.6.0-rc3-next20120823-1-iniza-generic_RCU-issue.txt" of type "text/plain" (90427 bytes)

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