I have a Dell XPS 15, and I’ve noticed that power management is definitely worse on kernel 5.10 than it is on kernel 5.9 (in 5.9 I get 5-6 hours of battery life with average usage, in 5.10 no more than 3 hours). Also, screen brightness adjustment works only in kernel 5.9 (and in no other one). Now, since 5.9 has already reached its end of life, I’m wondering for how long it will remain available for me in Manjaro Settings Manager.
Do I have to abandon it at some point?
Can you show result of
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
on 5.9 and then 5.10?
It’s “powersave” on both. It might have to do with the fact (that I mentioned) that I can’t reduce screen brightness on kernel 5.10…
Right.
Kernel 5.9 is EOL and no longer maintained, you not getting security patches. I suggest to concentrate your efforts on getting brightness working again in 5.10. Once you done, you will be good for at least 2 years, possibly 4-5, as this is how long 5.10 will be maintained.
Thanks. I’ve solved installing icc-brightness. Now brightness works on 5.10 as well. Thanks a lot for your help!
Enjoy your Manjaro and 5.10 LTS kernel for next few years then 
I will. These laptops with OLED display and double video card are a bit a pain in the ass to configure (it’s the 5th laptop on which I install linux, and it’s been definitely the most demanding), but after a week it looks like I’ve reached some stability…
PCI-Express runtime power management for NVIDIA GPUs does not work on Linux 5.10 with NVIDIA driver 460.32.03 or older. The 460.39 driver version restores this functionality, but it’s only available in the unstable branch at the moment. This could explain the poorer battery life.
Thanks but this shouldn’t have been my case, as I’m not using the NVidia video card (and therefore I’m not using the NVidia driver). It was probably due to screen backlight that was not adjustable.