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Librem13: Enable SATA link power management by default
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Description

PureOS team to investigate SATA Linux Power Management for laptops;

  • Does PureOS have SATA Link Power Management enabled by default?
  • How do we add 'med_power_with_dipm' as default for at least Mini and laptops? Via Udev?
  • We could opt in via udev if we don't trust having it enabled for all devices but according to @nicole it boosts battery life considerably (it sure does on other harware i own)
  • Enabling SATA Link Power Management can and most likely will save 1W+ (if they have a SATA SSD installed) which can result in 1h or more battery runtime.

SATA Link Power Management can be enabled via sysfs

/sys/class/scsi_host/host<n>/link_power_management_policy

and Guido suggested to use the safe mode

med_power_with_dipm

Event Timeline

guido created this task.Tue, Oct 13, 01:31
jeremiah.foster triaged this task as High priority.

Following Guido's link, I ran

$  cat /sys/class/scsi_host/host*/link_power_management_policy
med_power_with_dipm
med_power_with_dipm

Which is, AIUI, the desired default setting for ALPM. It is possible that our kernel in Byzantium already has this as the as the default setting but more investigation is needed.

nicole added a comment.Wed, Oct 14, 02:06

Oh good!
Or also not so good, because then I wonder what people do with their laptops not getting more battery life... hmm...

guido added a comment.Wed, Oct 14, 05:32

@jeremiah.foster could you check if min_power makes a difference? It seems to save 0.5W here things are fluctuating quite a bit so a longer test would be good.

So how do we do this test in a way that produces useful data? Do we run it at two different settings on two laptops concurrently? Or should I measure battery level over time at specific intervals with each setting on the same device?

nicole added a comment.Wed, Oct 14, 08:12

Do you have an AC power meter? That's what I used... let the system sit there idle, battery fully charged, look at power consumption. Then just change _one_ thing at a time, let it settle and become idle again, measure again.

I have such a tool you can plg between the wall socket and the laptop power cord which displays Watt directly.

guido added a comment.Wed, Oct 14, 09:44

@jeremiah.foster powetop shows the amount of power drawn from the battery as a rough indicator

I don't have a power meter but I will use powertop. :-)

nicole added a comment.EditedWed, Oct 14, 10:16

This IIRC does not work with the Librem laptops since these do not measure the energy properly, instead just estimate based on discharge rate. And even if, it is really rough (even Thinkpads do a pretty bad job at it).