defaults: librem5-pm: Enable simple_ondemand governor for DRAM

Fixes linux#188 (closed)

Undrafting as the dependency has already been bumped enough in !350 (merged).

marked this merge request as ready

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• 6b183402...18925ab9 - 2 commits from branch Librem5:pureos/byzantium
• 1bd7d463 - defaults: librem5-pm: Enable simple_ondemand governor for DRAM

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• 1bd7d463...a16a0bf3 - 11 commits from branch Librem5:pureos/byzantium
• 576c4fae - defaults: librem5-pm: Enable simple_ondemand governor for DRAM

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I just did a simple test with a USB power meter to see the power draw over 5 minutes since running gnome-software in service mode using both powersave and simple_ondemand governor with screen off.

With powersave, packagekitd was keeping one CPU busy at 100% for slightly above 4 minutes. At the end of the 5 minutes period the power meter reading was 125mWh.

With simple_ondemand, packagekitd was done after slightly above one minute already, so the phone was idling rest of the time. Power meter reading was 109mWh (it was at about 45mWh at the moment when packagekitd finished its work).

I've also recorded two minutes of idling (nothing but kgx running): the result was the same for both governors - 28mWh; and two minutes of keeping all CPU cores busy with compressing random data: 61mWh for powersave and 99mWh for simple_ondemand.

This is consistent with my anecdata - simple_ondemand appears to save battery and makes the phone cooler. It also makes the UX much better when using the phone over ssh. The one case where it makes things worse - a rogue process constantly consuming 100% CPU in the background - is already a pathological case with poor results on both governors. When the process actually does some sensible and finite work, it's going to finish it much faster with simple_ondemand, saving plenty of power. Therefore, I'm going to merge this.

To go back to previous behavior, users can always use this udev rule:

SUBSYSTEM=="devfreq", TEST=="governor", ATTR{governor}="powersave"

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• e6259ad8 - defaults: librem5-pm: Enable simple_ondemand governor for DRAM

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merged