When does heir become executing on calling _Thread_Dispatch_request from another cpu?

[Richi Dubey]

I understand, Thank you for the clarification.

Last question:

_SMP_Preempt calls _Thread_Dispatch_update_heir which
calls _Thread_Dispatch_request which sends an interrupt
with _CPU_SMP_Send_interrupt.
This interrupt would have set the executing equal to heir but would've
taken unpredictable time, but explicitly
calling _Thread_Dispatch_enable(other_cpu) right after
_SMP_Preempt(...node_on_other_cpu...) sets the executing corresponding to
the other_cpu's cpu control right away, is that correct?

On Fri, Aug 21, 2020 at 2:52 PM Sebastian Huber <
sebastian.huber at embedded-brains.de> wrote:

> On 21/08/2020 11:12, Richi Dubey wrote:
>
> > Is it okay I directly call _Thread_Dispatch_enable while calling
> > SMP_Preempt (since the latter does not call it) on another processor?
> > This question is wrt the code at this line
> > <
> https://github.com/richidubey/rtems/blob/03d08d02b3e61570f2022845caa44ec6a261f677/cpukit/score/src/schedulerstrongapa.c#L245>.
>
> >
> The thread dispatching works with locks unrelated to the scheduler. It
> is all right do do thread dispatching in parallel to the execution of
> scheduler code. The scheduler data structures are protected by the
> scheduler lock.
> >
> > This question has comes up because set_affinity does the following in
> > the order:
> > _Scheduler_SMP_Preempt_and_schedule_highest_ready
> > set_affinity
> > enqueue.
> >
> > The strong APA's highest_ready preempt a different cpu and allocates a
> > thread. This CPU can again be preempted while calling the enqueue
> > corresponding to Strong APA, at which point it would require the
> > latest scheduled thread on it (the one just assigned it to by
> > highest_ready if it's the case).
> The scheduler code should only use the scheduler internal data
> structures. It should define which thread should execute on which
> processor. That a thread actually executes on the processor happens
> asynchronously to the scheduler operations and is not the business of
> the scheduler. This is the job of the thread dispatch code.
>
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