score: Simplify _Thread_Change_priority()

The function to change a thread priority was too complex.  Simplify it
with a new scheduler operation.  This increases the average case
performance due to the simplified logic.  The interrupt disabled
critical section is a bit prolonged since now the extract, update and
enqueue steps are executed atomically.  This should however not impact
the worst-case interrupt latency since at least for the Deterministic
Priority Scheduler this sequence can be carried out with a wee bit of
instructions and no loops.

Add _Scheduler_Change_priority() to replace the sequence of
  - _Thread_Set_transient(),
  - _Scheduler_Extract(),
  - _Scheduler_Enqueue(), and
  - _Scheduler_Enqueue_first().

Delete STATES_TRANSIENT, _States_Is_transient() and
_Thread_Set_transient() since this state is now superfluous.

With this change it is possible to get rid of the
SCHEDULER_SMP_NODE_IN_THE_AIR state.  This considerably simplifies the
implementation of the new SMP locking protocols.

1 files changed, 10 insertions, 18 deletions

diff --git a/cpukit/score/include/rtems/score/schedulersimpleimpl.h b/cpukit/score/include/rtems/score/schedulersimpleimpl.h
index c256071a8f..b73a1b2c78 100644
--- a/cpukit/score/include/rtems/score/schedulersimpleimpl.h
+++ b/cpukit/score/include/rtems/score/schedulersimpleimpl.h
@@ -38,24 +38,6 @@ RTEMS_INLINE_ROUTINE Scheduler_simple_Context *
   return (Scheduler_simple_Context *) _Scheduler_Get_context( scheduler );
 }
 
-/**
- * This routine puts @a the_thread on to the ready queue.
- *
- * @param[in] the_ready_queue is a pointer to the ready queue head
- * @param[in] the_thread is the thread to be blocked
- */
-RTEMS_INLINE_ROUTINE void _Scheduler_simple_Ready_queue_requeue(
-  const Scheduler_Control *scheduler,
-  Thread_Control          *the_thread
-)
-{
-  /* extract */
-  _Chain_Extract_unprotected( &the_thread->Object.Node );
-
-  /* enqueue */
-  _Scheduler_simple_Ready_queue_enqueue( scheduler, the_thread );
-}
-
 RTEMS_INLINE_ROUTINE bool _Scheduler_simple_Insert_priority_lifo_order(
   const Chain_Node *to_insert,
   const Chain_Node *next
@@ -102,6 +84,16 @@ RTEMS_INLINE_ROUTINE void _Scheduler_simple_Insert_priority_fifo(
   );
 }
 
+RTEMS_INLINE_ROUTINE void _Scheduler_simple_Extract(
+  const Scheduler_Control *scheduler,
+  Thread_Control          *the_thread
+)
+{
+  (void) scheduler;
+
+  _Chain_Extract_unprotected( &the_thread->Object.Node );
+}
+
 RTEMS_INLINE_ROUTINE void _Scheduler_simple_Schedule_body(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,