Re: [Xenomai-help] Scheduling questions...

[Philippe Gerum <rpm@xenomai.org>]

On Fri, 2011-03-25 at 16:43 -0400, Eric Eric wrote:
> What I'm really asking about is specifically the "unless" clause at
> the end of your response.  Assume a high priority RT thread is doing
> something like while(1) { } and just spinning and eating CPU.  I would
> like to force the Linux kernel to be scheduled for, say, up to 20mS
> every 200mS to give it the opportunity to service Linux interrupts
> even if the high-priority RT task is runnable (ie I want to
> periodically preempt the RT thread and allow the Linux kernel to run
> for a limited amount of time).  It looks like SCHED_SPORADIC is a way
> to do this, I'm just not sure how to apply that to the kernel itself.

Scheduling all threads your create within the SCHED_SPORADIC class, with
specifying a background priority set to -1 for all of them would do the
job.

> 
> Thanks,
> 
> - Eric
> 
> On Fri, Mar 25, 2011 at 3:59 PM, Philippe Gerum <rpm@xenomai.org> wrote:
> > On Fri, 2011-03-25 at 15:48 -0400, Eric Eric wrote:
> >> Roger on the RR/FIFO scheduling question.  Regarding Linux starvation,
> >> it looks like pthread_setschedparam_ex can be used on a particular
> >> Linux thread to avoid starvation, however I'm more concerned about the
> >> Linux kernel itself.  In the example below, I may want the kernel to
> >> have some time to service interrupts even if an RT task is behaving
> >> badly.  How could I achieve this?
> >
> > As an extension, Xenomai interprets param.low_prio == -1 as "suspend the
> > thread". So each time the thread exceed its runtime credit, the nucleus
> > suspends it until it is replenished, instead of merely downgrading its
> > priority. As a side-effect, Linux becomes runnable again (unless another
> > -rt thread is requesting the CPU immediately, but you get the point).
> >
> >>
> >> Thanks again for the fast and helpful responses!
> >>
> >> - Eric
> >>
> >> On Fri, Mar 25, 2011 at 4:21 AM, Philippe Gerum <rpm@xenomai.org> wrote:
> >> > On Thu, 2011-03-24 at 19:47 -0400, Eric Eric wrote:
> >> >> Hello, I've been reading through some of the documentation and have a
> >> >> few questions regarding scheduling:
> >> >>
> >> >> - API docs say that rt_task_set_mode can allow a task to undergo
> >> >> round-robin scheduling.  This seems to imply that we can have an
> >> >> environment of mixed round-robin and FIFO task scheduling.  Is this
> >> >> correct?  If so, what is the scheduling relationship between tasks
> >> >> running in FIFO and RR modes?
> >> >
> >> > RR are FIFO threads within the same priority group.
> >> >
> >> >>
> >> >> - I am concerned about Linux starvation.  For example, suppose a
> >> >> misbehaving RT task spins and burns CPU indefinitely (watchdog
> >> >> notwithstanding).  I would still like to preempt this task and allow
> >> >> Linux to run for up to some maximum time (say up to 30mS every 200mS).
> >> >>  So, if using RR scheduling, is there a way to use rt_task_slice to
> >> >> allocate time to Linux?  Is there a Linux shadow thread that I can
> >> >> allocate time to?
> >> >
> >> > Xenomai implements sporadic server scheduling. See SCHED_SPORADIC,
> >> > usable with int pthread_setschedparam_ex().
> >> >
> >> >>
> >> >> Thank you.
> >> >>
> >> >> - Eric
> >> >>
> >> >> _______________________________________________
> >> >> Xenomai-help mailing list
> >> >> Xenomai-help@domain.hid
> >> >> https://mail.gna.org/listinfo/xenomai-help
> >> >
> >> > --
> >> > Philippe.
> >> >
> >> >
> >> >
> >
> > --
> > Philippe.
> >
> >
> >

-- 
Philippe.