Re: Xterm Hangs - Possible scheduler defect?

[Lee Revell <rlrevell@joe-job.com>]

On Fri, 2005-02-25 at 15:53 +0000, Paulo Marques wrote:
> Ingo Oeser wrote:
> > Chris Friesen wrote:
> > 
> >>Ingo Oeser wrote:
> >>[...]
> > You would need to change the priority of task 1 until it releases the
> > mutex. Ideally the owner gets the maximum priority of
> > his and all the waiters on it, until it releases his mutex, where he regains
> > its old priority after release of mutex. But this priority elevation happens
> > only, if he is runnable. If not, he gets his old priority back, until he is 
> > runnable.
> 
> This is called a "priority inversion" problem, and there was some work 
> done by Ingo Molnar to make the scheduler aware of such cases and handle 
> them appropriatelly.
> 
> You can follow this thread for more info:
> 
> http://marc.theaimsgroup.com/?l=linux-kernel&m=110106915415886&w=2
> 

The solution to your problem (which is as old as the hills) involves
priority inheriting mutexes which are available in the RT preempt patch
(if you build with CONFIG_PREEMPT_RT).  This should be usable for hard
realtime applications.

http://people.redhat.com/mingo/realtime-preempt

If you just need very good soft realtime performance I recommend
PREEMPT_DESKTOP.

Lee