On Sat, Jun 20, 2020 at 6:12 AM Richi Dubey <richidu...@gmail.com> wrote:
>
> Hi,
>
> I've been learning how SMP scheduler word in RTEMS and I came across the
> following function definition:
> --------------------------------------------------------------------------------------------
>
> /**
> * @brief Allocates the cpu for the scheduled thread.
> *
> * Attempts to prevent migrations but does not take into account affinity.
> *
> * @param context The scheduler context instance.
> * @param scheduled The scheduled node that should be executed next.
> * @param victim If the heir is this node's thread, no processor is allocated.
> * @param[in, out] victim_cpu The cpu to allocate.
> */
>
> static inline void _Scheduler_SMP_Allocate_processor_lazy(
> Scheduler_Context *context,
> Scheduler_Node *scheduled,
> Scheduler_Node *victim,
> Per_CPU_Control *victim_cpu
> )
> {
> Thread_Control *scheduled_thread = _Scheduler_Node_get_user( scheduled );
> Thread_Control *victim_thread = _Scheduler_Node_get_user( victim );
> Per_CPU_Control *scheduled_cpu = _Thread_Get_CPU( scheduled_thread );
> Per_CPU_Control *cpu_self = _Per_CPU_Get();
> Thread_Control *heir;
>
> _Assert( _ISR_Get_level() != 0 );
>
> if ( _Thread_Is_executing_on_a_processor( scheduled_thread ) ) {
> if ( _Scheduler_SMP_Is_processor_owned_by_us( context, scheduled_cpu ) ) {
> heir = scheduled_cpu->heir;
> _Thread_Dispatch_update_heir(
> cpu_self,
> scheduled_cpu,
> scheduled_thread
> );
> } else {
> /* We have to force a migration to our processor set */
> heir = scheduled_thread;
> }
> } else {
> heir = scheduled_thread;
> }
>
> if ( heir != victim_thread ) {
> _Thread_Set_CPU( heir, victim_cpu );
> _Thread_Dispatch_update_heir( cpu_self, victim_cpu, heir );
> }
> }
>
>
> --------------------------------------------------------------------------------
> Can someone please help me understand what this function is trying to do and
> how exactly it is achieving that? I am finding it hard to understand the
> meaning and use of the terms like cpu_self (why do we need cpu_self ? Is it
> the CPU for scheduled or for victim?), _Thread_Is_executing_on_a_processor(
> scheduled_thread ): Why would we have the thread already executing when we
> need to allocate a processor to it? Why are we allocating a processor then?
>
Have you looked at how the function gets called/used? Or more
importantly, when it gets called?
you see cpu_self = Per_CPU_Get();
Have you looked at that function to see what it does yet? Does it need
better documentation/doxygen?
> Thanks,
> Richi.
>
> _______________________________________________
> devel mailing list
> devel@rtems.org
> http://lists.rtems.org/mailman/listinfo/devel
_______________________________________________
devel mailing list
devel@rtems.org
http://lists.rtems.org/mailman/listinfo/devel
