Sleep mode drains battery very fast
After resuming from suspend, use this command in the terminal:
journalctl -b | grep -i "should not be sleeping"
If you see this:
Oct 21 07:20:18 alien kernel: cache: parent cpu1 should not be sleeping
Oct 21 07:20:18 alien kernel: cache: parent cpu2 should not be sleeping
Oct 21 07:20:18 alien kernel: cache: parent cpu3 should not be sleeping
Oct 21 07:20:18 alien kernel: cache: parent cpu4 should not be sleeping
Oct 21 07:20:18 alien kernel: cache: parent cpu5 should not be sleeping
Oct 21 07:20:18 alien kernel: cache: parent cpu6 should not be sleeping
Oct 21 07:20:18 alien kernel: cache: parent cpu7 should not be sleeping
It could mean when you suspended the CPU's were not put to sleep as per his bounty Q&A a couple of years ago: systemd suspends system but upon resume kernel then enters sleep and wake-up
If so, I'm sad to report the problem persists to this day on my newest laptop just as it did on that older laptop.
Problem since 2012?
This old email chain: Re: Kernel stops at "PM: Preparing system for mem sleep", never makes it to "Freezing user space processes ... " has a similar problem.
From my log file today:
Oct 21 13:48:15 alien kernel: PM: Preparing system for sleep (mem)
Oct 21 13:48:16 alien acpid[964]: client 1171[0:0] has disconnected
Oct 21 13:48:32 alien kernel: Freezing user space processes ... (elapsed 0.003 seconds) done.
- Line 1 is normal
- Line 2 is abnormal and linked to old X11 crash bugs
- Line 3 is occurs after resuming but should have happened as part of suspend.
Some other interesting points is it often takes 5 to 8 seconds to suspend when it should be about 1 second. This bug is reported in many places too.
If you don't have the same problem in the previous sections and, your laptop stays warm when suspended, then your fix maybe here: Ubuntu 18.04 - Dell XPS13 9370 no longer suspends on lid close