Re: Real-Time Preemption, -RT-2.6.12-final-V0.7.51-06

William Weston
2005-07-07T18:53:44Z

On Thu, 7 Jul 2005, Ingo Molnar wrote:

> > Still looking into this issue on -51-06. Found something really odd:
> > SCHED_NORMAL tasks will start to inherit the priority value of some
> > other SCHED_FIFO task. If JACK is started at a given SCHED_FIFO
> > priority, X and all of its children will inherit the same priority
> > value after login. Other random processes will inherit this, too --
> > sometimes init...
> >
> > SCHED_NORMAL tasks suddenly inheriting priority values in the range
> > normally reserved for SCHED_FIFO could explain at least part of the
> > meltdown I've been seeing. Any thoughts?
>
> is this inheritance perpetual? It is normal for some tasks to be boosted
> momentarily, but if the condition remains even after jackd has exited,
> it's clearly an anomaly. (lets call it "RT priority leakage".) Priority
> leakage on SMP was fixed recently, but there could be other bugs
> remaining.

Yes, this leakage perpetual. That's what struck me as odd.

> There's priority-leakage debugging code in the -RT kernel, which is
> activated if you enable CONFIG_DEBUG_PREEMPT. This debugging code, if
> triggered, should produce 'BUG: comm/123 leaked RT prio 123 (123)?" type
> of messages. But ... due to a bug it would not print out anything but
> would lock up hard if it detects the condition (and if
> RT_DEADLOCK_DETECT is enabled). I have fixed this reporting bug in the
> -51-08 kernel.

-51-08 is building now. I'll check out the latest, too.

--ww