Toggle SATA ALPM (Agressive Link Power Management) on/off when on battery/mains

[Tore Anderson]

ALPM is a feature that enables SATA AHCI controllers to save some power at the expense of performance. This feature can be controlled from Linux since version 2.6.24 (I believe).

I've attached a script (based on /usr/lib/pm-utils/power.d/sched-powersave) that can be installed to /usr/lib/pm-utils/sata-alpm, and it will toggle the feature on/off when switching to battery/mains. I've verified that the scripts works as expected on my Lenovo ThinkPad X61s on a freshly updated Kubuntu Intrepid alpha-3.

Power management in Ubuntu is extremely confusing, with acpi-support, laptop-mode, pm-utils, HAL, and guidance-power-manager (and probably its GNOME counterpart) all doing many of the same things with considerable overlap. Hopefully someone will clean up this mess before Intrepid is released... Anyway, although handling power management features of the hard drive itself (hdparm -B) is done by laptop-mode and acpi-support (yes, both at the same time!), I submit this patch to pm-utils because scheduler power savings is enabled in a very similar way as SATA ALPM from pm-utils, so it kinda fit well here. If it's incorrect please reassign it and I will try to provide an updated patch.

Tore

[Henrique Ferreiro (henrique-ferreiro)]

This has been fixed in upstream pm-utils as of commit http://cgit.freedesktop.org/pm-utils/commit/?id=381ff7b01f459e5767d927386dad48e52d2c5f02