I'm having an issue with speed on a Dell C840 laptop running Ubuntu 9.04. I have found that it seems to want to throttle the CPU down as soon as the fan kicks in. When the temperature goes past 50C, the fan will start at full speed and the system will throttle down to state P6 (25%) as seen in the /proc/acpi/.../throttling file. Once the temperatur goes down (even below 43C), the fan never turns off and the throttling state never comes back to P0 (100%), so the system run poorly from that point out.

I was running 8.04 and the system worked fine for the longest time - fans came on and off as needed and never saw the throttling issue. I noticed this happening at some point (I assume I received an update, but don't know which one) and it's been happening ever since. I upgraded to 8.10 and it continued to happen and then upgraded to 9.04 this last week and it's still happening. I can watch the throttling file and as soon as the fan kicks in I see the state change.

I want to turn off this throttling control, as the laptop seems to run pretty cool. It's not under heavy use and if I can get the fans to come on and off as they did that would be great. It normally runs below 50C so I'm not concerned about overheating.

Any help will be very appreciated.

Try using this in a xterm as root.
You can add it to the bootup scripts to always keep the system in this state. Or you can modify the kernel to not use throttling, but that requires recompiling it. I tried searching for a boot method to disable it but I could not find anything and I don't have the kernel sources here to check the documentation.

Thanks for the reply. That refers to the CPU Frequency Scaling that essentially scales the frequency the CPU is running at. What I am experiencing is the CPU T-States, where the CPU is "put to sleep" for short amounts of time (like every Xth cycle is forced to be a sleep cycle). It appears that this is to prevent overheating of the system, but for some reason my laptop does not come out of these states.

When my fans kick in, I see in the /proc/acpi/.../throttling file that it is in state T6 which is essentaily 25% of the CPU cycles are non-sleep cycles.

state count: 8
active state: T0
state available: T0 to T7
states:
T0: 100%
T1: 87%
T2: 75%
T3: 62%
T4: 50%
T5: 37%
*T6: 25%
T7: 12%

The fans never go off and the system stays in this state - which is very poor performance.

Ahh ok. T-States are considered a relic of the past since they do almost nothing these days to save power. Thats strange that you go into that state. There must be a way to change it manually using /sys, but I have so far come up blank.