I recently found this on Google:

echo 0 >> /sys/devices/system/cpu/cpu1/online

in order to offline a cpu.

I tried, it seemed to work but powertop doesn't show me a difference of Watt consumption, is it normal ??
Because it could save lot of energy if laptop is used to simple things like using openoffice with battery for example.

What do you think about this ?

As far as i know, this won't work.
You can't shut down a single core manually, because the older cpus don't have technology implemented to allow them that. Newer ones do, but it's automatic.

Kernel may cut-off a single cpu, but in my opinion it'll continue working in the background.

Did you ever notice how many of intel cpus have the same physical characteristics (die size, number of transistors, package size), and that they consume similar amount of energy no matter how much slower or faster they are ?

on whih cpu's is it implemented ?

I thought it was the 'idle states" specification which is implemented on new penryn generation.

you can shutdown one core of a dual core cpu but the only result will be that you can't use it. the power consumption will be the same because you can not switch off just one core of a cpu.

this feature is for multi cpu systems where a cpu can be REALLY shutdown (switched off)

K_O-Gnom

like i5 where there is 2 cpu and 4threads ?

thankl for your answer

i think the i5 as dual core also don't support real shutdown of one core. you need 2 hardware cpus that you can shutdown one and save power.

K_O-Gnom