Re: SCHED_FIFO and SCHED_RR in 2.4.7-10custom kernel

[Nicolas Bonnefon <nicolas.bonnefon@fr.thalesgroup.com>]

> My application uses the possibility to change scheduling mechanism. When
> changing from SCHED_OTHER to SCHED_FIFO or SCHED_RR, my application causes
> the whole Linux PC to "hang". Prior to launching my own application, I
> launch a "superbash" application with higher priority than my own
> application. But I am not able to switch to the window where this
> "superbash" application is running to kill my own application. The PC
> simply does not respond to any input from the keyboard.

Have you tried without running X ?
A SCHED_FIFO or SCHED_RR task has ALWAYS priority over any SCHED_OTHER
task, so if your application sits in an infinite loop without blocking, the 
window manager cannot preempt it and you simply cannot switch x-term.
I think you should carefully debug your app in SCHED_OTHER mode first, and 
then switch to some real-time policy.

>
> I have used this mechanism before, and I am quite confident that this
> worked under kernel 2.4.2. Are you aware of anything that could explain
> this behaviour?

It would be surprising, but if you were sure of that, it would deserve some 
deeper investigations !

Regards
-- 
Nicolas Bonnefon
Radar Development/Digital Processing Engineer
Thales Air Defence - 7-9 rue des Mathurins
92223 Bagneux - France