strange processor (slow on AC, normal on battery)

[strawks <strawks@yahoo.fr>]

Hello all,

I have an Asus A6VA laptop (Intel Centrino, 1.8GHz Pentium-M).

On Linux 2.6.18-3, when running on battery, the system works fine. But
when I plug the AC adapter, the system is very slow, CPU frequency stays
often below 40MHz. Running the following commands, CPU frequency goes up
to 1.8GHz after ~0.5 seconde and the system runs fine :
nice -20 bash -c "for((;;)); do echo -n; done"

Removing the processor module (rmmod processor) solve this issue but of
course I have no more control over CPU frequency.
Inserting the module with max_cstate=1 also solves this issue, and I can
change CPU frequency with cpufreq-set.

I have installed the same kernel on 3 (one of which is a Medion with
Centrino) other laptops and 2 desktop computers without encounting this
behaviour.

This problem is present since the first 2.6.17 stock kernel.

I'm currently staying with the stock 2.6.16-2 kernel since this is the
last working kernel on my laptop.

Does anyone have seen the same behaviour on another laptop or desktop?


Googling around didn't get me anything.

Any hint would be appreciated.

regards,
strawks