Re: [patch] voluntary-preempt-2.6.8.1-P3

Elladan
2004-08-18T21:30:01Z

On Wed, Aug 18, 2004 at 03:01:48PM +0200, Florian Schmidt wrote:
> On Wed, 18 Aug 2004 14:27:03 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
> >
> > > Btw: one question: at one point in time the IRQ handlers were in the
> > > SCHED_FIFO scheduling class. Why has this changed?
> >
> > so that they dont starve the audio threads by default - the audio IRQ
> > has to get another priority anyway. Maybe we could try a default
> > SCHED_FIFO prio lower than the typical rt_priority of jackd - e.g. 30?
>
> Oh, upon rereading the chrt manpage i found out why i failed to set them
> to SCHED_FIFO manually. So it was my error. I thought the
> scheduling of the IRQ handlers was not changable at runtime. Thus my
> question to make them SCHED_FIFO by default.
>
> Well, i still think they should be SCHED_FIFO by default, so no user
> process that is not itself SCHED_FIFO can starve them [X11 was able to
> starve mouse irq's on my system with the defualt IRQ handlers
> running SCHED_OTHER FWIW]. To make starving of user-SCHED_FIFO processes
> unprobably maybe use a default static prio of 0.
>
> Afaik jackd uses priorities > 0 for its audio threads when runing
> SCHED_FIFO anyways..
>
> But since the user will have to tweak his IRQ handlers manually anyways
> [set soundcard irq higher prio than the rest, etc..], it doesn't really
> make a difference.

This doesn't take into account SCHED_RR processes, which expect to
behave just like SCHED_FIFO unless there's another SCHED_RR process of
the same priority...

-J