Messages in this thread |  | | Subject | Re: [PATCH v2] sched: rt: Make RT capacity aware | From | Valentin Schneider <> | Date | Mon, 3 Feb 2020 17:15:01 +0000 |
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On 03/02/2020 16:14, Steven Rostedt wrote: > On Mon, 3 Feb 2020 14:27:14 +0000 > Qais Yousef <qais.yousef@arm.com> wrote: > >> I don't see one right answer here. The current mechanism could certainly do >> better; but it's not clear what better means without delving into system >> specific details. I am open to any suggestions to improve it. > > The way I see this is that if there's no big cores available but little > cores are, and the RT task has those cores in its affinity mask then > the task most definitely should consider moving to the little core. The > cpu_find() should return them! > > But, what we can do is to mark the little core that's running an RT > task on a it that prefers bigger cores, as "rt-overloaded". This will > add this core into the being looked at when another core schedules out > an RT task. When that happens, the RT task on the little core will get > pulled back to the big core. >
That sounds sensible enough - it's also very similar to what we have for CFS, labeled under "misfit tasks" (i.e. tasks that are "too big" for LITTLEs).
> > Note, this will require a bit more logic as the overloaded code wasn't > designed for migration of running tasks, but that could be added. >
I haven't adventured too much within RT land, but FWIW that's what we use the CPU stopper for in CFS (see active_load_balance_cpu_stop()).
> -- Steve >
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