> > On a Dell Precision 3540/0M14W7 with Debian sid/unstable restoring the > keyboard backlight takes over 100 ms according to `systemd-analyze > critical-chain` [1]. > > ``` > $ systemd-analyze critical-chain > […] > └─sysinit.target @887ms > └─systemd-backlight@leds:dell::kbd_backlight.service > @1.295s +114ms > └─system-systemd\x2dbacklight.slice @1.294s > └─system.slice @291ms > └─-.slice @291ms > ``` > > I have to run the program [2] under strace to know for sure, that the > delay is caused by accessing the backlight device. Unfortunately, the > device is already in use by somebody else, so debugging is not easy. > Maybe you have some hint, how to approach analysis from the Linux kernel > side. > > The way the keyboard backlight control works it does go into dell-laptop which invokes a SMI to interact with a BIOS defined SMM interface. This unfortunately is going to be slow and cumbersome. I don't know any way to improve it, and I would suggest that systemd should not be changing the backlight during the bootup, the firmware will be keeping the last value configured for you.
