linux-kernel - excessive kworker CPU wakeups

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Date:	Fri, 02 Dec 2011 15:38:40 -0500
From:	"David H. Durgee" <dhdurgee@...izon.net>
To:	linux-kernel@...r.kernel.org
Cc:	Tejun Heo <tj@...nel.org>
Subject: excessive kworker CPU wakeups

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, who is cc'd, 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?

Dave
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