cpu frequency scaling makes movie playback choppy

[Dennis Noordsij]

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 <email address hidden>, 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

[Dennis Noordsij (dennis-noordsij)]

The culprit turns out to be:

analyzing CPU 1:
  no or unknown cpufreq driver is active on this CPU

Apparantly on this laptop (Dell D630) something goes wrong with acpi-cpufreq after suspend-resume. I tried it now on a fresh boot, and now I get:

cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006
Report errors and bugs to <email address hidden>, please.
analyzing CPU 0:
  driver: acpi-cpufreq
  CPUs which need to switch frequency at the same time: 0 1
  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.
analyzing CPU 1:
  driver: acpi-cpufreq
  CPUs which need to switch frequency at the same time: 0 1
  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.

and playback is just fine, the CPU being at full speed the whole time.

Since the problem is actually caused by something else, I am marking this as invalid.

[Dennis Noordsij (dennis-noordsij)]

Caused by #183033 (after doing a suspend-resume)