Re: Real-Time Preemption, -RT-2.6.12-final-V0.7.51-12

Peter Zijlstra
2005-07-09T21:24:07Z

On Fri, 2005-07-08 at 13:12 -0700, William Weston wrote:
> On Fri, 8 Jul 2005, Ingo Molnar wrote:
>
> > could you check whether the priority leakage happens if you disable SMP?
> > (if you can reproduce it easily)
>
> No priority leakages have been seen with UP configs on any of the
> machines I've been testing.
>
> The leakage is not hard to reproduce under SMT: start up jackd from a
> text vc with an rt prio of 60 (or some unique prio above the IRQ threads),
> then restart X and login. After several minutes, X and all of its
> children will be running at whatever prio jackd was started at (but still
> SCHED_NORMAL). Eventually, init, a handful of SCHED_NORMAL kernel
> threads, and other random processes are all running at the same priority.
> When reset to default priority with chrt or schedtool, these processes
> eventually revert back to the leaked priority level. When jackd is
> stopped, the priorities stay in their elevated state. If jackd is not
> started before logging in to X, then the priority of one of the SCHED_FF
> kernel threads is leaked to other processes in the same manner.
>

I can reproduce priority leakage on my SMP system; any userspace process
chrt'ed up and a lot will follow. This makes the system very
unresponsive when doing a make -j5. Verified on 51-{6,18,23}.

--
Peter Zijlstra <a.p.zijlstra@chello.nl>