0,250,500,1000 is better than 0,125,500,1000

and yes, n900 sleeps at 0

Ok , now I'm using this .

FREQS="0:20,90 250:30 500:38,360 1000:60,500"
UP_THRESHOLD=75
SAMPLING_RATE=150000

Voltages are good ?

overclocking _will_ shorten the lifetime of your device - probably dramatically

yup, voltages are normal now.

each device has a processor with different yields, you might be able to go lower, but you have to experiment.

if the voltage too low, it will just restart and you have to change the voltage again and try.

mine is 0:25, 250:25, 500:35, 1000:60

some people go much much lower.

you can create copies of the included profiles and modify them further. those are lv, ulv, xlv and ideal

but do remember what you modify so that you know what caused the device to freeze and adjust that value. so always keep a reference copy once you reach a stable voltage.

most importantly, change one value at a time and test it, or else you wont know which value caused the freezing/rebooting.

ideal methods to test would be to play a media file while online using wifi and loading some video from youtube for e.g. - use your imagination.

install conky as well to see what is the processor doing when running tasks in the background

htop also is a good application to monitor running daemons and apps but conky is more graphical and shows more information at a glance

try this first,

0:20, 250:30, 500:38, 1000:56

if it is stable at that for a day, running multiple tasks, try this

0:20, 250:30, 500:38, 1000:52

if it crashes at 52 try 54

you get the idea

and then once you find a stable voltage for 1000 for e.g. 56, then adjust the voltage for 500, for e.g. 34

0:20, 250:30, 500:34, 1000:56

its a very logical method to find all the lowest voltages for each frequency.

and remember, stability is more important than lowest possible voltage, because if its unstable and reboots - you know how much battery rebooting process eats ???

Won't decreasing sampling time increase overhead just like increasing the amount of different frequencies available increases overhead?

@jananan - thanks for advices mate , I am familiar with overclocking because I used to overclock my pc a lot , I spent a lot of time finding good voltages and other parameters . I will try some tweaks tomorrow .

I am permanently running at 1000 min max lv with 0 issues.

going beyond that = 1150 min max lv will cause random reboots in watching videos, playing webos games, watching streaming videos... but very erratic. sometimes it's ok for a day or two but sometimes, it just doesn't accept it... but it's ULTRA smooth at 1150.

1000 min max is already very smooth honestly. try it

Nobody should be using a minimum frequency of 125MHz.
Stock N900 uses 250 min 600 max.
If you use 125MHz minimum frequency, it may lag.
This was also noted out by Titan. (maker of power kernel)

I'm running 0-500-600-750 XLV up_th=75, rate 300000.
Everything is so much smoother now.

Oddly, all apps run fine on XLV, while videos just don't play, and I need to load default to play videos. Is this the result of extreme undervolting?

Yes , I tried overclocking on XLV too and it crashes on some apps . By the way , what battery life you have with these settings ?