realtime render thread

[nekopsykose]

e.g. like sway https://github.com/swaywm/sway/blob/5be5a5005164d3ccff844f4c72836cb49cbf784a/sway/realtime.c#L19 and kwin https://invent.kde.org/plasma/kwin/-/blob/b0970bd6c7c481f210c9bfcd205292cfcbbcba34/src/utils/realtime.cpp#L22 and mutter https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2060 and pipewire module-rt https://gitlab.freedesktop.org/pipewire/pipewire/-/blob/589a06e105838c482dd25518766d8b96a79710c4/src/modules/module-rt.c#L567

the three ways are using RTKit via dbus, or using pthread_setschedparam/syscall via libc::, or using RealtimeThreadSchedulePolicy in https://docs.rs/thread-priority/latest/thread_priority (but i have no idea how to integrate that to the render thread only)

it (hopefully) would lead to slightly improved presentation under load

[YaLTeR]

This is actually also quite hard to get right, both the thread part and the realtime part. I closely followed the development in mutter, and they kept running into endless issues where the driver just took slightly too long to process a drm commit synchronously, running mutter over the realtime deadline, and killing it. Or taking a little too long to process a commit asynchronously, leading to random frame drops. I'd rather avoid dealing with that until later, when easier optimizations are done.

[nekopsykose]

I'd rather avoid dealing with that until later, when easier optimizations are done.

sure, of course :)

running mutter over the realtime deadline, and killing it.

this sounds interesting, i didn't know there was some deadline you can't run over (for sched_rr anyway). do you have a link to some discussion?

[YaLTeR]

See for example this MR and linked issue: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3324

[nekopsykose]

i see, that's very interesting. thanks!