(I originally asked this in another thread, but it got lost in the debate on another matter.)

Looking at this page it seems that setting NO_HZ in the kernel config leads to significant power saving.

Before I find out the hard way, can anyone confirm this in slackware 13 and advise of any potential drawbacks in setting NO_HZ? (Must be a reason why PV didn't set it.)

What hard way? If you don't like it, just reboot with your original kernel.

Never had problems with tickless kernel, but just make sure you keep your old kernel in lilo in case something does go wrong.

Just keeping another kernel (image) in lilo isn't quite enough. I had to take care of the modules too, including some (e.g. vboxdrv) that I'd compiled outside the kernel source. I'm a bit out of practice at compiling kernels so I did find this quite hard to get right. Also I'm working on a laptop I used for work so messing things up is a big deal.

From what I could glean from a search of the internet, it seems that the timer tick is more of a legacy thing and there is no real downside to a tickless kernel.

I didn't see a huge saving in power from going tickless, probably because the intel Atom processor (it's in an asus eee pc 1000h) consumes so little power. The C2 state uses only slightly more power than C4 and even at full tilt in C0 state the power increase is only a couple of watts.

However, I did get powertop to show we how to save a few watts of power. So running slack13 with kde 4.2.4 and wireless I dropped from 13W down to 10.5W pushing battery life from about 4 up to almost 5 hours under light use. The main power saving seemed to be switching off power to usb devices that weren't active, in particular the built-in webcam. To achieve this I followed powertop's advice and added this to lilo.conf
but this didn't quite work. I also added this to rc.local to stop the webcam getting power when inactive:
Hope this is useful to someone.

I heard VirtualBox doesn't get along well with a tickless system. Otherwise I always just keep my system at 1000Hz to play it safe. Would be interested to know of tickless drawbacks as well.

ah, I started up virtual box but only to check it works. Will give it a more thorough test drive and let you know the results.

that's a pretty impressive power savings for just turning off the USB not in use, wowzers!

How is this still working out for you? If you decide to use a device that was asleep, will it really wake-up? Have you seen any issues as a result of suspend to ram/disk at all?

Lucky you. I get whining capacitors at 1000hz.

I'm running a tickless kernel right now. I haven't noticed a difference though.

Virtual box seems equally happy with the tickless kernel as it was under the stock generic kernel.

The usb devices I use are all fine in waking up after being powered down as described above. I did read reports of usb printers having problems with this, but I never use a printer so I can't comment.

If anything, I have the opposite problem: it seems that the usb devices are woken up for reasons I don't understand, so my power saving mentioned above is hard to sustain in practice. Oh well, 4 hours isn't bad

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