[Intel-gfx] [RFC 0/8] Force preemption

[Chris Wilson]

Quoting Joonas Lahtinen (2018-03-23 13:20:40)
> So far nobody has been succesful in selling this to the userspace
> compositors (the most likely user) or has somebody?

I hadn't even contemplated selling it. However, it does seem applicable
to the RealTime priorities for Vk and 
https://www.khronos.org/registry/EGL/extensions/NV/EGL_NV_context_priority_realtime.txt

Gah. More fiddling with EGL...

Personally I don't think I'd want X/gnome-shell/weston to adopt a
RealTime or bust philosophy (i.e. I'm not planning to send a patch to
raise weston from PRIORITY_HIGH to PRIORITY_RT), but that doesn't mean
there aren't scenarios where it will be important.

So a context param, say PREEMPT_TIMEOUT in ns with 0 meaning disable and
bounded by CAP_SYS_NICE. Too soft? CAP_SYS_ADMIN, since it's about
giving permission to nuke others? Implementation side, having it on the
context is a fiddle, but we should be able to set a queue_timeout
at the same time as setting queue_priority to save having to find the
preempting context at irq time.
-Chris