Re: [RFC PATCH v2 6/6] sched/fair: Implement starvation monitor

From: peterz
Date: Fri Aug 07 2020 - 10:11:57 EST

On Fri, Aug 07, 2020 at 03:49:41PM +0200, luca abeni wrote:
> Hi Peter,
> peterz@xxxxxxxxxxxxx wrote:

> > One thing I considerd was scheduling this as a least-laxity entity --
> > such that it runs late, not early
> Are you thinking about scheduling both RT and non-RT tasks through
> deadline servers? If yes,

Maybe, I initially considered this for mixed criticality, where the
'soft' class would run EDF and the 'hard' class would run LLF (or the
other way around, I can't quite remember how I figured it).

If you restrict the hard class to single CPU assignment (IOW the UP
case) and ensure that u_llf + U_gedf/N < 1, it should just work out.

But I shelved all that after I heard about that other balancer idea
Danial was suppose to be working on ;-)))

> then I think that using something like
> laxity-based scheduling for the SCHED_OTHER server can be a good idea
> (but then we need to understand how to combine deadline-based
> scheduling with laxity-based scheduling, etc...)

/me consults notes, EDZL is I think the closest thing there.

> Or are you thinking about keeping the SCHED_OTHER server throttled
> until its laxity is 0 (or until its laxity is lower than some small
> value)? In this second case, the approach would work even if RT tasks
> are not scheduled through a server (but I do not know which kind of
> performance guarantee we could provide).

That would certainly be sufficient for OTHER servers I think.