About EDF SMP Behaviour

[Sebastian Huber]

On 17/05/2021 08:17, Richi Dubey wrote:
> 
> Can someone please explain this behavior of EDF SMP Scheduler on a 4 CPU 
> system, with INIT task pinned to cpu 0:
> 
> 
> Before Task 3 (Priority 6, Affined to CPU 3) arrival:
> 
> CPU 1 is executing: Task 1 (Priority 5, Affined to CPU 1)
> CPU 2 is executing: Task 2 (Priority 7, Affined to CPU 2)
> CPU 3 is executing: Task 0 (Priority 3, Affined to ALL)
> 
> After Task 3 arrival:
> CPU 1 is executing: Task 1 (Priority 5, Affined to CPU 1)
> CPU 2 is executing: Task 0 (Priority 3, Affined to ALL)
> CPU 3 is executing: Task 3 (Priority 6, Affined to CPU 3)
> 
> How did Task 3 force Task 0 out of its CPU when Task 0 has a higher 
> priority? 

Task 0 still has a processor, it just moved from CPU 3 to 2. Task 3 can 
only use CPU 3.

> Is thread helping involved?

No, thread helping is only involved if you use mutexes.

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