score: Improve scheduler helping protocol

Only register ask for help requests in the scheduler unblock and yield
operations.  The actual ask for help operation is carried out during
_Thread_Do_dispatch() on a processor related to the thread.  This yields
a better separation of scheduler instances.  A thread of one scheduler
instance should not be forced to carry out too much work for threads on
other scheduler instances.

Update #2556.

11 files changed, 67 insertions, 132 deletions

diff --git a/cpukit/score/include/rtems/score/scheduler.h b/cpukit/score/include/rtems/score/scheduler.h
index fd59f16dee..1b9509ae4f 100644
--- a/cpukit/score/include/rtems/score/scheduler.h
+++ b/cpukit/score/include/rtems/score/scheduler.h
@@ -42,16 +42,6 @@ struct Per_CPU_Control;
 
 typedef struct Scheduler_Control Scheduler_Control;
 
-#if defined(RTEMS_SMP)
-  typedef bool Scheduler_Void_or_bool;
-
-  #define SCHEDULER_RETURN_VOID_OR_BOOL return false
-#else
-  typedef void Scheduler_Void_or_bool;
-
-  #define SCHEDULER_RETURN_VOID_OR_BOOL return
-#endif
-
 /**
  * @brief The scheduler operations.
  */
@@ -63,7 +53,7 @@ typedef struct {
   void ( *schedule )( const Scheduler_Control *, Thread_Control *);
 
   /** @see _Scheduler_Yield() */
-  Scheduler_Void_or_bool ( *yield )(
+  void ( *yield )(
     const Scheduler_Control *,
     Thread_Control *,
     Scheduler_Node *
@@ -77,7 +67,7 @@ typedef struct {
   );
 
   /** @see _Scheduler_Unblock() */
-  Scheduler_Void_or_bool ( *unblock )(
+  void ( *unblock )(
     const Scheduler_Control *,
     Thread_Control *,
     Scheduler_Node *
diff --git a/cpukit/score/include/rtems/score/schedulercbs.h b/cpukit/score/include/rtems/score/schedulercbs.h
index e56747bdc5..635abce125 100644
--- a/cpukit/score/include/rtems/score/schedulercbs.h
+++ b/cpukit/score/include/rtems/score/schedulercbs.h
@@ -146,7 +146,7 @@ typedef struct {
  */
 extern Scheduler_CBS_Server _Scheduler_CBS_Server_list[];
 
-Scheduler_Void_or_bool _Scheduler_CBS_Unblock(
+void _Scheduler_CBS_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/scheduleredf.h b/cpukit/score/include/rtems/score/scheduleredf.h
index 9fc2eb9ea3..91c303ca56 100644
--- a/cpukit/score/include/rtems/score/scheduleredf.h
+++ b/cpukit/score/include/rtems/score/scheduleredf.h
@@ -144,7 +144,7 @@ void _Scheduler_EDF_Node_initialize(
   Priority_Control         priority
 );
 
-Scheduler_Void_or_bool _Scheduler_EDF_Unblock(
+void _Scheduler_EDF_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
@@ -166,7 +166,7 @@ Priority_Control _Scheduler_EDF_Unmap_priority(
   Priority_Control         priority
 );
 
-Scheduler_Void_or_bool _Scheduler_EDF_Yield(
+void _Scheduler_EDF_Yield(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/schedulerimpl.h b/cpukit/score/include/rtems/score/schedulerimpl.h
index 90a9bcca68..53631ab4e5 100644
--- a/cpukit/score/include/rtems/score/schedulerimpl.h
+++ b/cpukit/score/include/rtems/score/schedulerimpl.h
@@ -113,6 +113,43 @@ RTEMS_INLINE_ROUTINE void _Scheduler_Release_critical(
 #endif
 }
 
+#if defined(RTEMS_SMP)
+/**
+ * @brief Registers an ask for help request.
+ *
+ * The actual ask for help operation is carried out during
+ * _Thread_Do_dispatch() on a processor related to the thread.  This yields a
+ * better separation of scheduler instances.  A thread of one scheduler
+ * instance should not be forced to carry out too much work for threads on
+ * other scheduler instances.
+ *
+ * @param[in] the_thread The thread in need for help.
+ */
+RTEMS_INLINE_ROUTINE void _Scheduler_Ask_for_help( Thread_Control *the_thread )
+{
+  _Assert( _Thread_State_is_owner( the_thread ) );
+
+  if ( the_thread->Scheduler.helping_nodes > 0 ) {
+    ISR_lock_Context  lock_context;
+    Per_CPU_Control  *cpu;
+
+    _Thread_Scheduler_acquire_critical( the_thread, &lock_context );
+    cpu = _Thread_Get_CPU( the_thread );
+    _Per_CPU_Acquire( cpu );
+
+    _Chain_Append_unprotected(
+      &cpu->Threads_in_need_for_help,
+      &the_thread->Scheduler.Help_node
+    );
+
+    _Per_CPU_Release( cpu );
+    _Thread_Scheduler_release_critical( the_thread, &lock_context );
+
+    _Thread_Dispatch_request( _Per_CPU_Get(), cpu );
+  }
+}
+#endif
+
 /**
  * The preferred method to add a new scheduler is to define the jump table
  * entries and add a case to the _Scheduler_Initialize routine.
@@ -159,64 +196,17 @@ RTEMS_INLINE_ROUTINE void _Scheduler_Schedule( Thread_Control *the_thread )
  */
 RTEMS_INLINE_ROUTINE void _Scheduler_Yield( Thread_Control *the_thread )
 {
-#if defined(RTEMS_SMP)
-  Chain_Node              *node;
-  const Chain_Node        *tail;
-  Scheduler_Node          *scheduler_node;
   const Scheduler_Control *scheduler;
   ISR_lock_Context         lock_context;
-  bool                     needs_help;
-
-  node = _Chain_First( &the_thread->Scheduler.Scheduler_nodes );
-  tail = _Chain_Immutable_tail( &the_thread->Scheduler.Scheduler_nodes );
-
-  scheduler_node = SCHEDULER_NODE_OF_THREAD_SCHEDULER_NODE( node );
-  scheduler = _Scheduler_Node_get_scheduler( scheduler_node );
-
-  _Scheduler_Acquire_critical( scheduler, &lock_context );
-  needs_help = ( *scheduler->Operations.yield )(
-    scheduler,
-    the_thread,
-    _Thread_Scheduler_get_home_node( the_thread )
-  );
-  _Scheduler_Release_critical( scheduler, &lock_context );
-
-  if ( !needs_help ) {
-    return;
-  }
-
-  node = _Chain_Next( node );
-
-  while ( node != tail ) {
-    bool success;
-
-    scheduler_node = SCHEDULER_NODE_OF_THREAD_SCHEDULER_NODE( node );
-    scheduler = _Scheduler_Node_get_scheduler( scheduler_node );
-
-    _Scheduler_Acquire_critical( scheduler, &lock_context );
-    success = ( *scheduler->Operations.ask_for_help )(
-      scheduler,
-      the_thread,
-      scheduler_node
-    );
-    _Scheduler_Release_critical( scheduler, &lock_context );
-
-    if ( success ) {
-      break;
-    }
-
-    node = _Chain_Next( node );
-  }
-#else
-  const Scheduler_Control *scheduler;
 
   scheduler = _Thread_Scheduler_get_home( the_thread );
+  _Scheduler_Acquire_critical( scheduler, &lock_context );
   ( *scheduler->Operations.yield )(
     scheduler,
     the_thread,
     _Thread_Scheduler_get_home_node( the_thread )
   );
-#endif
+  _Scheduler_Release_critical( scheduler, &lock_context );
 }
 
 /**
@@ -293,64 +283,17 @@ RTEMS_INLINE_ROUTINE void _Scheduler_Block( Thread_Control *the_thread )
  */
 RTEMS_INLINE_ROUTINE void _Scheduler_Unblock( Thread_Control *the_thread )
 {
-#if defined(RTEMS_SMP)
-  Chain_Node              *node;
-  const Chain_Node        *tail;
-  Scheduler_Node          *scheduler_node;
   const Scheduler_Control *scheduler;
   ISR_lock_Context         lock_context;
-  bool                     needs_help;
-
-  node = _Chain_First( &the_thread->Scheduler.Scheduler_nodes );
-  tail = _Chain_Immutable_tail( &the_thread->Scheduler.Scheduler_nodes );
-
-  scheduler_node = SCHEDULER_NODE_OF_THREAD_SCHEDULER_NODE( node );
-  scheduler = _Scheduler_Node_get_scheduler( scheduler_node );
-
-  _Scheduler_Acquire_critical( scheduler, &lock_context );
-  needs_help = ( *scheduler->Operations.unblock )(
-    scheduler,
-    the_thread,
-    scheduler_node
-  );
-  _Scheduler_Release_critical( scheduler, &lock_context );
-
-  if ( !needs_help ) {
-    return;
-  }
-
-  node = _Chain_Next( node );
-
-  while ( node != tail ) {
-    bool success;
-
-    scheduler_node = SCHEDULER_NODE_OF_THREAD_SCHEDULER_NODE( node );
-    scheduler = _Scheduler_Node_get_scheduler( scheduler_node );
-
-    _Scheduler_Acquire_critical( scheduler, &lock_context );
-    success = ( *scheduler->Operations.ask_for_help )(
-      scheduler,
-      the_thread,
-      scheduler_node
-    );
-    _Scheduler_Release_critical( scheduler, &lock_context );
-
-    if ( success ) {
-      break;
-    }
-
-    node = _Chain_Next( node );
-  }
-#else
-  const Scheduler_Control *scheduler;
 
   scheduler = _Thread_Scheduler_get_home( the_thread );
+  _Scheduler_Acquire_critical( scheduler, &lock_context );
   ( *scheduler->Operations.unblock )(
     scheduler,
     the_thread,
     _Thread_Scheduler_get_home_node( the_thread )
   );
-#endif
+  _Scheduler_Release_critical( scheduler, &lock_context );
 }
 
 /**
diff --git a/cpukit/score/include/rtems/score/schedulerpriority.h b/cpukit/score/include/rtems/score/schedulerpriority.h
index 91ebb3852a..f5ae66102d 100644
--- a/cpukit/score/include/rtems/score/schedulerpriority.h
+++ b/cpukit/score/include/rtems/score/schedulerpriority.h
@@ -128,7 +128,7 @@ void _Scheduler_priority_Schedule(
   Thread_Control          *the_thread
 );
 
-Scheduler_Void_or_bool _Scheduler_priority_Unblock(
+void _Scheduler_priority_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
@@ -147,7 +147,7 @@ void _Scheduler_priority_Node_initialize(
   Priority_Control         priority
 );
 
-Scheduler_Void_or_bool _Scheduler_priority_Yield(
+void _Scheduler_priority_Yield(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/schedulerpriorityaffinitysmp.h b/cpukit/score/include/rtems/score/schedulerpriorityaffinitysmp.h
index d1275bc727..850c72bb40 100644
--- a/cpukit/score/include/rtems/score/schedulerpriorityaffinitysmp.h
+++ b/cpukit/score/include/rtems/score/schedulerpriorityaffinitysmp.h
@@ -96,7 +96,7 @@ void _Scheduler_priority_affinity_SMP_Block(
   Scheduler_Node          *node
 );
 
-bool _Scheduler_priority_affinity_SMP_Unblock(
+void _Scheduler_priority_affinity_SMP_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/schedulerprioritysmp.h b/cpukit/score/include/rtems/score/schedulerprioritysmp.h
index 75cc9b6e67..6671da5b7a 100644
--- a/cpukit/score/include/rtems/score/schedulerprioritysmp.h
+++ b/cpukit/score/include/rtems/score/schedulerprioritysmp.h
@@ -115,7 +115,7 @@ void _Scheduler_priority_SMP_Block(
   Scheduler_Node          *node
 );
 
-bool _Scheduler_priority_SMP_Unblock(
+void _Scheduler_priority_SMP_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *thread,
   Scheduler_Node          *node
@@ -156,7 +156,7 @@ Thread_Control *_Scheduler_priority_SMP_Remove_processor(
   struct Per_CPU_Control  *cpu
 );
 
-bool _Scheduler_priority_SMP_Yield(
+void _Scheduler_priority_SMP_Yield(
   const Scheduler_Control *scheduler,
   Thread_Control          *thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/schedulersimple.h b/cpukit/score/include/rtems/score/schedulersimple.h
index 1d97e1cd7d..0d410d5676 100644
--- a/cpukit/score/include/rtems/score/schedulersimple.h
+++ b/cpukit/score/include/rtems/score/schedulersimple.h
@@ -92,7 +92,7 @@ void _Scheduler_simple_Schedule(
   Thread_Control          *the_thread
 );
 
-Scheduler_Void_or_bool _Scheduler_simple_Yield(
+void _Scheduler_simple_Yield(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
@@ -104,7 +104,7 @@ void _Scheduler_simple_Block(
   Scheduler_Node          *node
 );
 
-Scheduler_Void_or_bool _Scheduler_simple_Unblock(
+void _Scheduler_simple_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/schedulersimplesmp.h b/cpukit/score/include/rtems/score/schedulersimplesmp.h
index 0cf3877b43..bc75b205d5 100644
--- a/cpukit/score/include/rtems/score/schedulersimplesmp.h
+++ b/cpukit/score/include/rtems/score/schedulersimplesmp.h
@@ -98,7 +98,7 @@ void _Scheduler_simple_SMP_Block(
   Scheduler_Node          *node
 );
 
-bool _Scheduler_simple_SMP_Unblock(
+void _Scheduler_simple_SMP_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *thread,
   Scheduler_Node          *node
@@ -139,7 +139,7 @@ Thread_Control *_Scheduler_simple_SMP_Remove_processor(
   struct Per_CPU_Control  *cpu
 );
 
-bool _Scheduler_simple_SMP_Yield(
+void _Scheduler_simple_SMP_Yield(
   const Scheduler_Control *scheduler,
   Thread_Control          *thread,
   Scheduler_Node          *node
diff --git a/cpukit/score/include/rtems/score/schedulersmpimpl.h b/cpukit/score/include/rtems/score/schedulersmpimpl.h
index 92a22d2ff8..7a281277fa 100644
--- a/cpukit/score/include/rtems/score/schedulersmpimpl.h
+++ b/cpukit/score/include/rtems/score/schedulersmpimpl.h
@@ -962,7 +962,7 @@ static inline void _Scheduler_SMP_Block(
   }
 }
 
-static inline bool _Scheduler_SMP_Unblock(
+static inline void _Scheduler_SMP_Unblock(
   Scheduler_Context     *context,
   Thread_Control        *thread,
   Scheduler_Node        *node,
@@ -972,7 +972,6 @@ static inline bool _Scheduler_SMP_Unblock(
 {
   Scheduler_SMP_Node_state  node_state;
   bool                      unblock;
-  bool                      needs_help;
 
   node_state = _Scheduler_SMP_Node_state( node );
   unblock = _Scheduler_Unblock_node(
@@ -986,6 +985,7 @@ static inline bool _Scheduler_SMP_Unblock(
   if ( unblock ) {
     Priority_Control new_priority;
     bool             prepend_it;
+    bool             needs_help;
 
     new_priority = _Scheduler_Node_get_priority( node, &prepend_it );
     (void) prepend_it;
@@ -1004,11 +1004,11 @@ static inline bool _Scheduler_SMP_Unblock(
       _Assert( node->idle == NULL );
       needs_help = true;
     }
-  } else {
-    needs_help = false;
-  }
 
-  return needs_help;
+    if ( needs_help ) {
+      _Scheduler_Ask_for_help( thread );
+    }
+  }
 }
 
 static inline void _Scheduler_SMP_Update_priority(
@@ -1069,7 +1069,7 @@ static inline void _Scheduler_SMP_Update_priority(
   }
 }
 
-static inline bool _Scheduler_SMP_Yield(
+static inline void _Scheduler_SMP_Yield(
   Scheduler_Context     *context,
   Thread_Control        *thread,
   Scheduler_Node        *node,
@@ -1095,7 +1095,9 @@ static inline bool _Scheduler_SMP_Yield(
     needs_help = true;
   }
 
-  return needs_help;
+  if ( needs_help ) {
+    _Scheduler_Ask_for_help( thread );
+  }
 }
 
 static inline void _Scheduler_SMP_Insert_scheduled_lifo(
diff --git a/cpukit/score/include/rtems/score/schedulerstrongapa.h b/cpukit/score/include/rtems/score/schedulerstrongapa.h
index 29dee66c44..d961f20c68 100644
--- a/cpukit/score/include/rtems/score/schedulerstrongapa.h
+++ b/cpukit/score/include/rtems/score/schedulerstrongapa.h
@@ -115,7 +115,7 @@ void _Scheduler_strong_APA_Block(
   Scheduler_Node          *node
 );
 
-bool _Scheduler_strong_APA_Unblock(
+void _Scheduler_strong_APA_Unblock(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node
@@ -156,7 +156,7 @@ Thread_Control *_Scheduler_strong_APA_Remove_processor(
   struct Per_CPU_Control  *cpu
 );
 
-bool _Scheduler_strong_APA_Yield(
+void _Scheduler_strong_APA_Yield(
   const Scheduler_Control *scheduler,
   Thread_Control          *the_thread,
   Scheduler_Node          *node