[Bug 223556] [NEW] cpu frequency scaling makes movie playback choppy

[Dennis Noordsij]

Public bug reported:

Binary package hint: linux-image

Ubuntu by default enables frequency scaling, which is very nice. Most of
the time, the CPU is running at 36% (using the ondemand governor).

When watching a movie in which some scenes are just a bit too much for
800 MHz (the 36% setting), the ondemand governor is not able to switch
up-and-down well enough to prevent choppy playback; the movie becomes
unwatchable. When the performance governor is selected (which is not
easily done through the UI afaik?) the movie of course plays flawlessly.

Since it heavily depends on the movie and system used, I don't think it's possible to set it as a reference. It's high-res (bluray) movie, CPU is a:
    Intel(R) Core(TM)2 Duo CPU     T7500  @ 2.20GHz

I've tried lowering the
/sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate down to
10,000 (default in Ubuntu kernel is 80,000) but it does not really make
a difference.

If there is some way to debug this in order to improve the behaviour of
the ondemand/conservative governor (it happens with both) I would like
to try.

I am not sure what would otherwise be the correct fix or workaround, but
as it is now, with a default desktop, movie playback can be choppy
because of the cpu frequency scaling, which I guess leaves most users
wondering why it isn't playing properly. Also, enabling the performance
governor is not that obvious (the first place to look for this option
would be in the cpu-frequency applet), but afaik it's not really
anywhere in the UI.


cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006
Report errors and bugs to linux at brodo.de, please.
analyzing CPU 0:
  driver: acpi-cpufreq
  CPUs which need to switch frequency at the same time: 0
  hardware limits: 800 MHz - 2.20 GHz
  available frequency steps: 2.20 GHz, 2.20 GHz, 1.60 GHz, 1.20 GHz, 800 MHz
  available cpufreq governors: powersave, ondemand, conservative, userspace, performance
  current policy: frequency should be within 800 MHz and 2.20 GHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 800 MHz (asserted by call to hardware).
analyzing CPU 1:
  no or unknown cpufreq driver is active on this CPU

** Affects: linux-meta (Ubuntu)
     Importance: Undecided
         Status: New

-- 
cpu frequency scaling makes movie playback choppy
https://bugs.launchpad.net/bugs/223556
You received this bug notification because you are a member of Kernel
Bugs, which is subscribed to linux-meta in ubuntu.