score: Introduce CPU budget operations

This patch set replaces the CPU budget algorithm enumeration with a set of CPU
budget operations which implement a particular CPU budget algorithm.  This
helps to hide the CPU budget algorithm implementation details from the general
thread handling.  The CPU budget callouts are turned into CPU budget
operations.  This slightly reduces the size of the thread control block.

All schedulers used the default scheduler tick implementation.  The tick
scheduler operation is removed and the CPU budget operations are directly used
in _Watchdog_Tick() if the executing thread uses a CPU budget algorithm.  This
is performance improvement for all threads which do not use a CPU budget
algorithm (default behaviour).

1 files changed, 8 insertions, 3 deletions

diff --git a/cpukit/score/src/threaddispatch.c b/cpukit/score/src/threaddispatch.c
index 1d317ad2b1..a53c8de2b0 100644
--- a/cpukit/score/src/threaddispatch.c
+++ b/cpukit/score/src/threaddispatch.c
@@ -275,7 +275,8 @@ void _Thread_Do_dispatch( Per_CPU_Control *cpu_self, ISR_Level level )
   executing = cpu_self->executing;
 
   do {
-    Thread_Control *heir;
+    Thread_Control                     *heir;
+    const Thread_CPU_budget_operations *cpu_budget_operations;
 
     level = _Thread_Preemption_intervention( executing, cpu_self, level );
     heir = _Thread_Get_heir_and_make_it_executing( cpu_self );
@@ -292,8 +293,12 @@ void _Thread_Do_dispatch( Per_CPU_Control *cpu_self, ISR_Level level )
      *  Since heir and executing are not the same, we need to do a real
      *  context switch.
      */
-    if ( heir->budget_algorithm == THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE )
-      heir->cpu_time_budget = rtems_configuration_get_ticks_per_timeslice();
+
+    cpu_budget_operations = heir->CPU_budget.operations;
+
+    if ( cpu_budget_operations != NULL ) {
+      ( *cpu_budget_operations->at_context_switch )( heir );
+    }
 
     _ISR_Local_enable( level );