So, which method of powersaving do You prefer?

Question

I just got a new laptop and I'm currently looking into my powersaving script again to see how much battery life I can squeeze out. I'm reading up on alot of things and just came across three different methods to achieve the same, e.g. enable powersaving:
1. You can pass the options through modprobe at boot;
2. You can pass the options directly to the kernel at boot;
3. You can set them at runtime
For example, USB autosave can be enabled in either of the following methods:
1. /etc/modprobe.d/usbcore.conf
options usbcore autosuspend=1
2. Kernel boot options (ie. in grub's menu.lst):
usbcore.autosuspend=1
3. At runtime, per device, with:
for i in /sys/bus/usb/devices/*/power/autosuspend; do echo 1 > $i; done
for i in /sys/bus/usb/devices/*/power/level; do echo auto > $i; done
Now I'm curious, which way do you prefer and why? I think I would prefer setting them all at runtime, just so I have all the different options (including those that can not be set by modprobe or directly at the kernel) grouped together in a script - but perhaps you can convince me of the better way!
EDIT: Oh, and of course there also are udev rules! Of course, kernel parameters and modprobe values do not enable toggling, so these might be less favored.
Last edited by Unia (2013-09-23 19:21:35)

Answer 1

Honestly, I just did what powertop told me to do.  So, at the time, I just googled things one by one, but I have since found out that you can output an html file from powertop that will tell you what to write to which files in order to set them to to "good".
It highly depends on your system and what modules and hardware you have.  So it is rather pointless to simply copy and paste the numerous configurations here.  But in general, if the option/file shown by powertop is a in /sys/module typically there is a parameter that can be set when the module loads.  So in those cases, you can use /etc/modprobe.d.  For the others, you can typically just use udevadm to do an attribute walk and get a few parameters to individualize a given setting, and then of course set the actual file in question.
Here is an example of what I use to set the satalink power management:
ACTION=="add", KERNEL=="host*", SUBSYSTEM=="scsi_host", SUBSYSTEMS=="scsi", ATTR{link_power_management_policy}="min_power"
Module parameters should be fairly obvious how to set as well if you are willing to read the man page.  But here is an example of the snd_hda_intel module's powersave function:
% cat /etc/modprobe.d/snd_hda_intel.conf
options snd_hda_intel powersave=1
I guess the only other thing that I forgot to mention was a few sysctl.d (formerly sysctl.conf) settings that are recommended by powertop as well.  I know off the top of my head that it recommends you set /proc/sys/vm/laptop_mode to '5'.