lkml.org 
[lkml]   [2012]   [Jan]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Request for assistance - excessive kworker CPU wakeups
    David H. Durgee (dhdurgee@verizon.net) wrote:
    > Mandeep Singh Baines wrote:
    > >On Fri, Dec 9, 2011 at 1:27 PM, David H. Durgee<dhdurgee@verizon.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
    > dhdurgee@DHD-Z560 ~/Downloads $ grep ""
    > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate*
    > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate:10000
    > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate_max:4294967295
    > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate_min:10000
    > dhdurgee@DHD-Z560 ~/Downloads $ dmesg | grep -i nohz
    > dhdurgee@DHD-Z560 ~/Downloads $
    >
    > Does this explain what I am seeing? Does this square with the
    > observations in my spreadsheet? Does this suggest a means of
    > reducing these excessive wakeups? Is there more information I can
    > provide to suggest a course of action?
    >

    IIUC, you should be seeing 100 such events per second * number of CPUs.
    Is that what you are seeing? You could reduce this by changing HZ. Maybe
    change to CONFIG_HZ_100 in your .config from CONFIG_HZ_1000. That
    should reduce the number of events by a factor of 10.

    Regards,
    Mandeep

    > Dave


    \
     
     \ /
      Last update: 2012-01-26 00:47    [W:0.025 / U:93.056 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site