linux-kernel - Re: Request for assistance - excessive kworker CPU wakeups

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Date:	Wed, 25 Jan 2012 09:44:14 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	"David H. Durgee" <dhdurgee@...izon.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Request for assistance - excessive kworker CPU wakeups

On Fri, Dec 9, 2011 at 1:27 PM, David H. Durgee <dhdurgee@...izon.net> wrote:
> I recently purchased a Lenovo IdeaPad Z560, model 09143YU, and as I am not a
> Windows fan I installed Linux Mint 11 Katya x64 to use instead of the
> supplied W7.  I was encountering a known hang and had to upgrade to a later
> kernel, so I am now using the 2.6.38-11-generic #50-Ubuntu SMP Mon Sep 12
> 21:17:25 UTC 2011 x86_64 kernel.
>
> I had my first occasion to use the laptop for an extended period for the
> first time over the Thanksgiving holiday and I found it needed to be tuned.
>  I downloaded powertop and used it to discover where my problems were.
>  After addressing excessive i915 interrupts due to DRI the next most
> frequent cause of CPU wakeups is a kworker on the system.  A search lead to
> a post by Tejun, indicating the need to trace such issues. Running the trace
> showed that 1933 of 2748 events were of the form:
>
> <idle>-0     [000] 22005.355346: workqueue_queue_work: work
> struct=ffff8800bb411188 function=do_dbs_timer workqueue=ffff88012b5d2c00
> req_cpu=0 cpu=0
>
> Tejun indicated that this is a workitem used by cpufreq and likely caused by
> something else hitting the CPU frequently.  So how do I diagnose this
> further and isolate the cause for correction?
>
> If you would like a summary of this, download this spreadsheet:
>
> http://home.comcast.net/%7Eddurgee/Tracelog.ods
>
> If you would like to inspect the trace log itself:
>
> http://home.comcast.net/%7Eddurgee/tracelog.zip
>

Hi Dave,

I don't know the cpufreq code that well, but it seem that this
workqueue is schedule periodically. You
can examine the sampling rate via /sys:

$ grep "" /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate*

Just curious, are you running nohz:

$ dmesg | grep -i nohz

Regards,
Mandeep

> Dave
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