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SubjectRe: voluntary-preempt-2.6.9-rc3-mm3-T3
FromLee Revell <>
DateSat, 09 Oct 2004 01:31:26 -0400
On Sat, 2004-10-09 at 01:23, Con Kolivas wrote:
> Lee Revell wrote:
> > On Sat, 2004-10-09 at 01:09, Con Kolivas wrote:
> > 
> >>Lee Revell writes:
> >>
> >>
> >>>On Thu, 2004-10-07 at 06:52, Ingo Molnar wrote:
> >>>
> >>>>i've released the -T3 VP patch:
> >>>>
> >>>>  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc3-mm3-T3
> >>>>
> >>>
> >>>With VP and PREEMPT in general, does the scheduler always run the
> >>>highest priority process, or do we only preempt if a SCHED_FIFO process
> >>>is runnable?
> >>
> >>Always the highest priority runnable.
> >>
> > 
> > 
> > Hmm, interesting.  Would there be any advantage to a mode where only
> > SCHED_FIFO tasks can preempt?  This seems like a much lighter way to
> > solve the realtime problem.
> 
> No, the linux scheduler has always been preemptible. PREEMPT and VP just 
> allows it to preempt kernel code paths as well. It could be modified to 
> do such a thing but apart from real time applications it would perform 
> very badly overall.

I am talking about a mode where we only allow a SCHED_FIFO process to
preempt a kernel code path.  In every other case it works like !PREEMPT.

This is apparently how kernel preemption worked on SVR4.

Lee 

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