Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.43-00

Esben Nielsen
2005-04-04T23:14:14Z

On Mon, 4 Apr 2005, Zwane Mwaikambo wrote:

> On Mon, 4 Apr 2005, Steven Rostedt wrote:
>
> > On Mon, 2005-04-04 at 22:47 +0200, Ingo Molnar wrote:
> >
> > > > Currently my fix is in yield to lower the priority of the task calling
> > > > yield and raise it after the schedule. This is NOT a proper fix. It's
> > > > just a hack so I can get by it and test other parts.
> > >
> > > yeah, yield() is a quite RT-incompatible concept, which could livelock
> > > an upstream kernel just as much - if the task in question is SCHED_FIFO.
> > > Almost all yield() uses should be eliminated from the upstream kernel,
> > > step by step.
> >
> > Now the question is, who will fix it? Preferably the maintainers, but I
> > don't know how much of a priority this is to them. I don't have the time
> > now to look at this and understand enough about the code to be able to
> > make a proper fix, and I'm sure you have other things to do too.
>
> I'm sure a lot of the yield() users could be converted to
> schedule_timeout(), some of the users i saw were for low memory conditions
> where we want other tasks to make progress and complete so that we a bit
> more free memory.
>

Easy, but damn ugly. Completions are the right answer. The memory system
needs a queue system where tasks can sleep (with a timeout) until the
right amount of memory is available instead of half busy-looping.

Esben