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, 38 insertions, 3 deletions

diff --git a/cpukit/score/src/schedulercbs.c b/cpukit/score/src/schedulercbs.c
index 8e5bf86f27..bedaf8e1da 100644
--- a/cpukit/score/src/schedulercbs.c
+++ b/cpukit/score/src/schedulercbs.c
@@ -21,10 +21,17 @@
 #endif
 
 #include <rtems/score/schedulercbsimpl.h>
+#include <rtems/score/statesimpl.h>
+#include <rtems/score/threadcpubudget.h>
 
-void _Scheduler_CBS_Budget_callout(
-  Thread_Control *the_thread
-)
+/**
+ * @brief Invoked when a limited time quantum is exceeded.
+ *
+ * This routine is invoked when a limited time quantum is exceeded.
+ *
+ * @param the_thread The thread that exceeded a limited time quantum.
+ */
+static void _Scheduler_CBS_Budget_callout( Thread_Control *the_thread )
 {
   Scheduler_CBS_Node      *node;
   Scheduler_CBS_Server_id  server_id;
@@ -52,6 +59,34 @@ void _Scheduler_CBS_Budget_callout(
   }
 }
 
+static void _Scheduler_CBS_Budget_at_tick( Thread_Control *the_thread )
+{
+  uint32_t budget_available;
+
+  if ( !the_thread->is_preemptible ) {
+    return;
+  }
+
+  if ( !_States_Is_ready( the_thread->current_state ) ) {
+    return;
+  }
+
+  budget_available = the_thread->CPU_budget.available;
+
+  if ( budget_available == 1 ) {
+    the_thread->CPU_budget.available = 0;
+    _Scheduler_CBS_Budget_callout ( the_thread );
+  } else {
+    the_thread->CPU_budget.available = budget_available - 1;
+  }
+}
+
+const Thread_CPU_budget_operations _Scheduler_CBS_Budget = {
+  .at_tick = _Scheduler_CBS_Budget_at_tick,
+  .at_context_switch = _Thread_CPU_budget_do_nothing,
+  .initialize = _Thread_CPU_budget_do_nothing
+};
+
 int _Scheduler_CBS_Initialize(void)
 {
   return SCHEDULER_CBS_OK;