score: Add thread priority to scheduler nodes

The thread priority is manifest in two independent areas.  One area is
the user visible thread priority along with a potential thread queue.
The other is the scheduler.  Currently, a thread priority update via
_Thread_Change_priority() first updates the user visble thread priority
and the thread queue, then the scheduler is notified if necessary.  The
priority is passed to the scheduler via a local variable.  A generation
counter ensures that the scheduler discards out-of-date priorities.

This use of a local variable ties the update in these two areas close
together.  For later enhancements and the OMIP locking protocol
implementation we need more flexibility.  Add a thread priority
information block to Scheduler_Node and synchronize priority value
updates via a sequence lock on SMP configurations.

Update #2556.

1 files changed, 21 insertions, 10 deletions

diff --git a/cpukit/score/src/scheduleredfchangepriority.c b/cpukit/score/src/scheduleredfchangepriority.c
index a0f5ec7061..9a73128e4c 100644
--- a/cpukit/score/src/scheduleredfchangepriority.c
+++ b/cpukit/score/src/scheduleredfchangepriority.c
@@ -36,31 +36,42 @@ Priority_Control _Scheduler_EDF_Unmap_priority(
   return priority & ~SCHEDULER_EDF_PRIO_MSB;
 }
 
-Scheduler_Void_or_thread _Scheduler_EDF_Change_priority(
+Scheduler_Void_or_thread _Scheduler_EDF_Update_priority(
   const Scheduler_Control *scheduler,
-  Thread_Control          *the_thread,
-  Priority_Control         new_priority,
-  bool                     prepend_it
+  Thread_Control          *the_thread
 )
 {
   Scheduler_EDF_Context *context;
   Scheduler_EDF_Node    *node;
+  Priority_Control       priority;
+  bool                   prepend_it;
+
+  if ( !_Thread_Is_ready( the_thread ) ) {
+    /* Nothing to do */
+    SCHEDULER_RETURN_VOID_OR_NULL;
+  }
 
-  context = _Scheduler_EDF_Get_context( scheduler );
   node = _Scheduler_EDF_Thread_get_node( the_thread );
+  priority = _Scheduler_Node_get_priority( &node->Base, &prepend_it );
 
-  if ( ( new_priority & SCHEDULER_EDF_PRIO_MSB ) != 0 ) {
-    node->background_priority = new_priority;
+  if ( priority == node->current_priority ) {
+    /* Nothing to do */
+    SCHEDULER_RETURN_VOID_OR_NULL;
   }
 
-  node->current_priority = new_priority;
+  if ( ( priority & SCHEDULER_EDF_PRIO_MSB ) != 0 ) {
+    node->background_priority = priority;
+  }
+
+  node->current_priority = priority;
+  context = _Scheduler_EDF_Get_context( scheduler );
 
   _Scheduler_EDF_Extract( context, node );
 
   if ( prepend_it ) {
-    _Scheduler_EDF_Enqueue_first( context, node, new_priority );
+    _Scheduler_EDF_Enqueue_first( context, node, priority );
   } else {
-    _Scheduler_EDF_Enqueue( context, node, new_priority );
+    _Scheduler_EDF_Enqueue( context, node, priority );
   }
 
   _Scheduler_EDF_Schedule_body( scheduler, the_thread, false );