Need help in figuring out how to allocate sizes to the array

[Gedare Bloom]

Resending without some stray words

On Thu, Aug 13, 2020 at 10:10 AM Gedare Bloom <gedare at rtems.org> wrote:
>
> On Thu, Aug 13, 2020 at 9:28 AM Richi Dubey <richidubey at gmail.com> wrote:
> >
> > Thanks,
> >
> > But I still can't find the code that links the 'Ready' in this
> >
> > >>  #define RTEMS_SCHEDULER_EDF_SMP( name ) \
> > >>      static struct { \
> > >>        Scheduler_EDF_SMP_Context Base; \
> > >>        Scheduler_EDF_SMP_Ready_queue Ready[ CONFIGURE_MAXIMUM_PROCESSORS
> > >> + 1 ]; \
> >
> In memory this structure will look like this:
> { Scheduler_SMP_Context, int64_t, Chain_Control,
> Scheduler_EDF_SMP_Ready_queue[CONFIGURE_MAXIMUM_PROCESSORS + 1] }
> Because the Scheduler_EDF_SMP_Context type comes first and provides
> { Scheduler_SMP_Context, int64_t, Chain_Control,
> Scheduler_EDF_SMP_Ready_queue[0] } where the last element is a 0-value
> array so it doesn't actually take up any memory storage, then the
> Scheduler_EDF_SMP_Ready_queue Ready[ CONFIGURE_MAXIMUM_PROCESSORS + 1]
> overlaps with the Scheduler_EDF_SMP_Ready_queue[0] because the end of
> Base aligns with the start of Ready.
>
> This is what I meant by you need to review how C struct layout works.
>
>
>
> > to the 'Ready' in scheduleredfsmp.h:
> >
> > typedef struct {
> >   Scheduler_SMP_Context Base;
> >
> >   /**
> >    * @brief Current generation for LIFO (index 0) and FIFO (index 1) ordering.
> >    */
> >   int64_t generations[ 2 ];
> >
> >   /**
> >    * @brief Chain of ready queues with affine threads to determine the highest
> >    * priority ready thread.
> >    */
> >   Chain_Control Affine_queues;
> >
> >   /**
> >    * @brief A table with ready queues.
> >    *
> >    * The index zero queue is used for threads with a one-to-all processor
> >    * affinity.  Index one corresponds to processor index zero, and so on.
> >    */
> >   Scheduler_EDF_SMP_Ready_queue Ready[ RTEMS_ZERO_LENGTH_ARRAY ];
> > } Scheduler_EDF_SMP_Context;
> >
> > If I figure this out, everything else would make sense too. Please help me out.
> >
> > On Thu, Aug 13, 2020 at 8:47 PM Gedare Bloom <gedare at rtems.org> wrote:
> >>
> >> On Thu, Aug 13, 2020 at 8:34 AM Richi Dubey <richidubey at gmail.com> wrote:
> >> >
> >> > Thanks,
> >> >  I am assuming this is the code that allocates space:
> >> >
> >> >>  #define RTEMS_SCHEDULER_EDF_SMP( name ) \
> >> >>      static struct { \
> >> >>        Scheduler_EDF_SMP_Context Base; \
> >> >>        Scheduler_EDF_SMP_Ready_queue Ready[ CONFIGURE_MAXIMUM_PROCESSORS
> >> >> + 1 ]; \
> >> >>      } SCHEDULER_EDF_SMP_CONTEXT_NAME( name )
> >> >
> >> This is declaring a structure type that will have a particular format
> >> of the struct name.
> >>
> >> >
> >> > How do we use or refer to this 'Base'? How do we link this 'Ready' to the 'Ready' inside the EDF_SMP_Context?
> >> >
> >>
> >> This stuff gets set up during confdefs step. Eventually the scheduler
> >> contexts are instantiated in the scheduler table.
> >>
> >> confdefs/scheduler.h:
> >>     #define CONFIGURE_SCHEDULER RTEMS_SCHEDULER_EDF_SMP( dflt )
> >>
> >>     #define CONFIGURE_SCHEDULER_TABLE_ENTRIES \
> >>       RTEMS_SCHEDULER_TABLE_EDF_SMP( dflt, CONFIGURE_SCHEDULER_NAME )
> >> ....
> >> const Scheduler_Control _Scheduler_Table[] = {
> >>   CONFIGURE_SCHEDULER_TABLE_ENTRIES
> >> };
> >>
> >> This is where the space actually gets allocated, based on how
> >> CONFIGURE_SCHEDULER_TABLE_ENTRIES gets defined up to here from the CPP
> >> macros.
> >>
> >>
> >>
> >> > On Thu, Aug 13, 2020 at 6:17 PM Sebastian Huber <sebastian.huber at embedded-brains.de> wrote:
> >> > >
> >> > > On 13/08/2020 14:42, Richi Dubey wrote:
> >> > >
> >> > > > I want to use arrays with size _CONFIGURE_MAXIMUM_PROCESSORS. Is it
> >> > > > okay if I define the arrays with this size while writing the scheduler
> >> > > > strong APA header file? I am asking this because the value of this
> >> > > > header gets defined at the time the test case runs while the scheduler
> >> > > > gets linked to the test case at the time of linking. So how would it
> >> > > > work?
> >> > >
> >> > > Do NOT use _CONFIGURE_MAXIMUM_PROCESSORS.
> >> > >
> >> > > In <rtems/scheduler.h> please use something similar to the EDF scheduler
> >> > > instantiation:
> >> > >
> >> > > #ifdef CONFIGURE_SCHEDULER_EDF_SMP
> >> > >    #include <rtems/score/scheduleredfsmp.h>
> >> > >
> >> > >    #ifndef CONFIGURE_MAXIMUM_PROCESSORS
> >> > >      #error "CONFIGURE_MAXIMUM_PROCESSORS must be defined to configure
> >> > > the EDF SMP scheduler"
> >> > >    #endif
> >> > >
> >> > >    #define SCHEDULER_EDF_SMP_CONTEXT_NAME( name ) \
> >> > >      SCHEDULER_CONTEXT_NAME( EDF_SMP_ ## name )
> >> > >
> >> > >    #define RTEMS_SCHEDULER_EDF_SMP( name ) \
> >> > >      static struct { \
> >> > >        Scheduler_EDF_SMP_Context Base; \
> >> > >        Scheduler_EDF_SMP_Ready_queue Ready[ CONFIGURE_MAXIMUM_PROCESSORS
> >> > > + 1 ]; \
> >> > >      } SCHEDULER_EDF_SMP_CONTEXT_NAME( name )
> >> > >
> >> > >    #define RTEMS_SCHEDULER_TABLE_EDF_SMP( name, obj_name ) \
> >> > >      { \
> >> > >        &SCHEDULER_EDF_SMP_CONTEXT_NAME( name ).Base.Base.Base, \
> >> > >        SCHEDULER_EDF_SMP_ENTRY_POINTS, \
> >> > >        SCHEDULER_EDF_MAXIMUM_PRIORITY, \
> >> > >        ( obj_name ) \
> >> > >        SCHEDULER_CONTROL_IS_NON_PREEMPT_MODE_SUPPORTED( false ) \
> >> > >      }
> >> > >
> >> > >    /* Provided for backward compatibility */
> >> > >
> >> > >    #define RTEMS_SCHEDULER_CONTEXT_EDF_SMP( name, max_cpu_count ) \
> >> > >      RTEMS_SCHEDULER_EDF_SMP( name )
> >> > >
> >> > >    #define RTEMS_SCHEDULER_CONTROL_EDF_SMP( name, obj_name ) \
> >> > >      RTEMS_SCHEDULER_TABLE_EDF_SMP( name, obj_name )
> >> > > #endif
> >> > >
> >> > _______________________________________________
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