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 Post subject: Load balancing tick
PostPosted: 11/11/2010, 17:11 
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Joined: 23/09/2010, 15:36
Posts: 7
Greeting,

using a NP220 running with lucid 10.04.
Code:
peter@rattir7:~$ uname -a
Linux rattir7 2.6.32-25-generic #46~ppa1~loms~lucid-Ubuntu SMP Fri Oct 22 23:33:19 UTC 2010 i686 GNU/Linux

I'm not using HAL and therefore have no laptop-mode.

As shown by powertop, the process [kernel scheduler] Load balancing tick is the main reason for waking up on my little box. On a standard user setting (firefox /w several tabs, nautilus, terminal, wlan) it typically rivals with firefox for the first place, sometimes about the double of amount (of ticks?), sometimes even more.

Example output of powertop:
Code:
peter@rattir7:~$ env LANG=en_EN.UTF8 sudo powertop -d
PowerTOP 1.12   (C) 2007, 2008 Intel Corporation

Collecting data for 15 seconds


Your CPU supports the following C-states : C1 C2 C4
Your BIOS reports the following C-states : C1 C2 C4
Cn             Avg residency
C0 (cpu running)        ( 6.8%)
polling        0.0ms ( 0.0%)
C1 mwait     0.2ms ( 0.1%)
C2 mwait     0.8ms ( 1.2%)
C4 mwait     5.6ms (91.9%)
P-states (frequencies)
  1.67 Ghz     3.5%
  1333 Mhz     0.3%
  1000 Mhz    96.2%
Disk accesses:
Wakeups-from-idle per second : 182.2   interval: 15.0s
Power usage (ACPI estimate): 6.1W (5.0 hours)
Top causes for wakeups:
  30.6% ( 70.8)   firefox-bin
  26.9% ( 62.1)   [kernel scheduler] Load balancing tick
  11.9% ( 27.6)   [uhci_hcd:usb5, eth1] <interrupt>
  11.4% ( 26.4)   [extra timer interrupt]
   4.3% ( 10.0)   xbindkeys
   3.6% (  8.4)   [kernel core] hrtimer_start (tick_sched_timer)
   2.6% (  6.1)   [kernel core] add_timer (wl_timer)

As far as I understand, the load balancing tick is a kernel issue cause of traditional linux kernels and can be made tickless to save some energy (-> http://www.lesswatts.org/projects/tickless/).

Also there is/was a bug in newer kernels (2.6.34) concerning this (-> https://groups.google.com/group/zen_kernel/browse_thread/thread/71a306f1a3a7b318).

No I ask myself if in your kernel we all use there may be the same or a similar bug, and if it would make sense to make the kernel tickless by default (if it isn't already).

If you think that is of importance, I would gladly help e.g. by compiling and testing such a kernel. But you needed to point me to the config and any obscure resources/patches of the recent ppa kernel.


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