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Linux Suspend Power Consumption

This article is about power use when suspended, there is another one about when running.

On a Lenovo ThinkPad X1 Yoga Gen6 (Type Number 20XY-004AMZ), I noticed the battery drained from 78% to 68% while the laptop was un-opened for 13h in Standby (sleep) mode.

According to this SO, if sudo cat /sys/power/mem_sleep shows [s2idle], then sudo -i and then echo 'deep' > /sys/power/mem_sleep should help.

When tried that, it failed with echo: write error: Invalid argument. This is because that "deep" suspend mode is not enabled in the BIOS. Rebooting into the BIOS and change the Suspend setting from the default something something Windows and Linux to the other choice about Linux S3 makes sudo cat /sys/power/mem_sleep show s2idle [deep].

With that Suspend still works. Waking up now needs to press the power button, not just any key. It's possible to re-authenticate with the Fingerprint reader, which is nice.

You will see Kernel logs (e.g. in dmesg) change from PM: suspend entry (s2idle) to PM: suspend entry (deep).

With that change, it went down only -3% from 26% to 23% in 6.5h on Standby. That seems ~30% better.

To get more (full, 0% use) power saving when un-used, you have to use Hibernate to Swap instead of Suspend.

PS: When we try to write s2idle into /sys/power/mem_sleep in that BIOS mode, Suspend is weird: The screen goes off, it seems like it's suspended (/sys/power/suspend_stats/fail* are all 0) - but the keyboard and the red ThinkPad light stay on! That's quite confusing... ;-) This is the "Suspend-to-Idle" mode that's described on Kernel doc power/interface.txt which you can also get with echo 'freeze' >/sys/power/state; where the echo 'mem' >/sys/power/state is the Suspend-to-RAM which one would normally want.

PPS: TODO Hibernates instead of Suspend, to save moar power?

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