Round-robing/timesliced tasks disturbed by rate-monotonic task

[Wendell Silva]

Hello RTEMS Gurus!

Environment:
  - RTEMS 4.10.2
  - BSP i386/pc386

Summary:
  - ticks per timeslice = 5
  - milliseconds per tick = 5
  - Task A, PREEMPT | TIMESLICE, priority = 10, "number crusher" never
yield CPU voluntarily.
  - Task B, PREEMPT | TIMESLICE, priority = 10, "number crusher" never
yield CPU voluntarily.
  - Task C, PREEMPT | NO_TIMESLECE, priority = 5, periodic
(rate-monotonic), period = 5 ticks (25ms), CPU usage = ~50%

What was expected:
  - Task C running periodically, as programmed.
  - Tasks A and A, using the remaining CPU budget, (~25% each one, in this
configuration).

What was observed:
  - Task C running periodically, as programmed (passed).
  - Only task A is running.
  - Task B never runs.

"Workarounds" applied to achieve the expected behavior:
   - 1: decrease ticks per timeslice; or,
   - 2: decrease task C CPU budget (larger period or less computations).

I believe the general form of the problem is equivalent to answer:
  - Why timesliced tasks gets starved, when:
       * ticks per timeslice is equals to a period of a RM task, or
       * when the CPU use of RM task is greater than or equals to 50%.

Is the RM scheduling police interfering in timeslice accounting?

Test program attached.

Run with:
  - qemu-system-i386 -kernel Debug/exer_rm

(it what tested in a real hardware and the same behavior was observed).

Change system.h and/or task_four to "fix".

Best regards,

--Wendell.
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