On Fri, 2011-03-25 at 21:52 +0100, Philippe Gerum wrote:
> 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.
SPORADIC threads are FIFO threads with a time budget.
>
> >
> > Thanks,
> >
> > - Eric
> >
> > On Fri, Mar 25, 2011 at 3:59 PM, Philippe Gerum <[email protected]> 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 <[email protected]> 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
> > >> >> [email protected]
> > >> >> https://mail.gna.org/listinfo/xenomai-help
> > >> >
> > >> > --
> > >> > Philippe.
> > >> >
> > >> >
> > >> >
> > >
> > > --
> > > Philippe.
> > >
> > >
> > >
>
--
Philippe.
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