fc2, xorg, 2.6.x, scheduling latency peaks

[Fernando Pablo Lopez-Lezcano]

On Wed, 2004-06-02 at 12:11, Fernando Pablo Lopez-Lezcano wrote:
> On Wed, 2004-06-02 at 11:34, Arjan van de Ven wrote:
> > On Wed, Jun 02, 2004 at 11:28:20AM -0700, Fernando Pablo Lopez-Lezcano wrote:
> > > > > > A real test with the Jack low latency server reveals that something else
> > > > > > is creating latency hits.
> > > > > 
> > > > > do you run Jack as realtime process ??
> > > > 
> > > > Correct, it is running SCHED_FIFO. I'm using Jack O'Quin LSM realcap
> > > > module to grant non-root users those privileges (compiled as a module in
> > > > the kernel). 
> > > > 
> > > > Just occured to me, is there anything else in FC2 that may be running
> > > > SCHED_FIFO?? I'll try to find out. 
> > > 
> > > Using schedutils (chrt) I find no tasks or threads running SCHED_FIFO.
> > > And the realtime threads of jack are apparently running SCHED_FIFO.
> > > Argh, that would have been too easy :-)
> > 
> > can you try to NOT run it realtime? 
> 
> Sure, just tried that. Lots _more_ xruns, move around the mouse, xruns,
> switch windows, xruns :-)
> 
> > Sounds odd but when you use realtime
> > behavior you have to be really careful for priority inversion situations (eg
> > if X doesn't run at such a high prio, but your RT task needs to wait on X to
> > draw something..)
> 
> Aha! I think you are on to something! I double checked the priority of
> the jack clients and _they_ are not getting SCHED_FIFO!! They should be
> getting that priority from the jack server but they are not (and the
> jack server is not complaining at all so no error is being raised).
> Probably some change in glibc, I would think... 

Before (or rather while) I start banging my head again against
sched_setscheduler and friends, could this be related to selinux even
though it is turned off? None of the calls that are supposed to give the
client thread SCHED_FIFO are (apparently) returning errors...

-- Fernando