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SubjectRe: low priority soft RT?
Hi!

> > > Anyone thought about allowing soft RT (SCHED_FIFO or SCHED_RR) tasks with
> > > negative priorities? These would only be executed if no other tasks of
> > > any type are there. Giving a normal Linux task a niceness value won't do
> > > this, as the task will still get some CPU time.
> >
> > So SCHED_IDLE then (only execute this if we would otherwise be
> > executing the idle task)? It's been talked about before, IIRC
> > even implemented, it just never got into the mainstream kernel.
>
> I have made a fairly substantial SCHED_IDLE patch, but due to
> the (never resolved) deadlock issues I haven't submitted it.
>
> OTOH, if we make SCHED_IDLE a sysctl tunable thing, we should
> be able to just ship it with the standard kernel and provide
> a Big Fat Warning(tm) along with it...

That's the bad solution. Right solution is to promote threads that are
in kernel mode to non-SCHED_IDLE priority. It should be well doable,
and IMO is required for patch to be usable.

What would you write to big fat warning?

"Random processes may freeze for random ammount of time if things go
wrong"?

Pavel
--
I'm really pavel@ucw.cz. Look at http://195.113.31.123/~pavel. Pavel
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