In an email thread with some colleagues, one of them mentioned that they had to force their laptop to use “deep” sleep instead of “s2idle”. This got me thinking - I’ve had the impression that my XPS13 sometimes doesn’t really suspend, and/or wakes up in the middle of the night, because the battery capacity sometimes is lower than it should be after being suspended overnight (going to sleep with 100% battery and having about 70% the morning afeter).

So I quickly looked up “s2idle” and landed here.

From here it looks like indeed s2idle is not really suspend-suspend and the system can wake up of its own accord according to unclear rules (or maybe they are clear, but I don’t care, I want the system to go to full sleep and only wake up when I open the lid or something similar). And it seems the way to get it to real deep-sleep is to write “deep” into /sys/power/mem_sleep. It further mentions that indeed s2idle is the default (which I confirmed by checking the above file), but it can be overridden by setting mem_sleep_default in the kernel command line.

It’s been a while since I last had to muck with GRUB configuration…

Just for kicks I also looked up mem_sleep_default and lo and behold, came upon a thread for the XPS 13 9310 (exactly the one I have).