Re: Scheduling behaviour issue

[Anh Vo <anhvofrcaus@gmail.com>]

On Wednesday, April 22, 2020 at 10:20:27 AM UTC-7, Simon Wright wrote:
> fabien.chouteau@gmail.com writes:
> 
> > On Wednesday, April 22, 2020 at 1:34:53 PM UTC+2, Simon Wright wrote:
> >> but FreeRTOS adds the preempted task at the *tail* of its ready queue
> >> ([4], section Prioritized Pre-emptive Scheduling (without Time Slicing),
> >> on page 95 or thereabouts).
> >
> > I couldn't find the paragraph that says that.
> 
> It's the dicussion after Figure 29.
> 
> There are 2 "continuous" tasks (no interaction with the scheduler) of
> the same priority, say A & B (this is so unlike any real-time system
> I've encountered! You might have just one, doing some sort of
> housekeeping or monitoring).
> 
> Both A and B are ready. One of the tasks, A, runs until a
> higher-priority task C preempts it; when the higher-priority task
> finishes, *the other task* B runs!
> 
> > That seems very strange to not resume the task that was just
> > preempted.
> 
> I so agree. I think it's because the mechanism used is derived from
> FreeRTOS's round-robin scheduler.

If the preempted task was resumed again, then task B will have no chance to run. Is it a undesired situation.