On 09/06/2020 12:26, Ralph Corderoy wrote: > I'd start with these two. The bug is probably LightDM's, e.g. it's > repeatedly asking Xorg to do some work on its behalf, though it might be > it's making a reasonable request which Xorg is doing inefficiently and > SDDM doesn't make the same request. I doubt it's the latter though > because Xorg is prodded by a lot of different client and a problem would > have already come to light. > > So, concentrating on LightDM, see if it has debug which you can enable > and find the output in the logs or journal. This might be the easiest > way to spot the problem, e.g. it's unhappy a file is missing. Ensure > the problem is occurring at the time, e.g. high CPU use. > > Next step would be to attach to it's running processes with strace(1) to > see what it's doing. ‘systemctl status lightdm.service’ will probably > show multiple process IDs to choose from, but not display the PIDs for > its threads. One way to obtain all of them is ‘sudo lsof > /usr/bin/lightdm’. > > Given those PIDs, ‘sudo strace -fp '42 314 1718'’ will attach to all of > them and any new children. You'll hopefully see they're all blocked, > i.e. consuming no resources. Many will be blocked on a file descriptor. > ‘sudo lsof -p 42’ will lists the FDs of PID 42, out of interest. > > Type a character into LightDM and see if it creates a flurry of > syscalls. They should die down to idle again. If not, there's your > clue. It might be sending a request to the Xorg X server over and over. > > strace's output can be stuffed to a file with -o instead of scrolling up > the screen. -e will let you filter out boring system calls, or > concentrate on particular ones, e.g. the ‘%desc’ set. > > Happy hunting!
Cheers for the advice. I just went about reinstalling lightdm on the thing, but it turns out that it doesn't work at all now, and also my trackpad doesn't work either, so, erm... I think I'll leave this one seeing as I no longer have any confidence that the hardware even still works properly, though it's probably more driver issues. I guess I could reinstall Mint, but for its current purpose (computing for Rosetta) the laptop is working okay so it's probably not a productive use of time. Hamish
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