[PATCH 2/2] score: Replace the single use of a sequence lock

[Sebastian Huber]

In SMP configurations, on 64-bit architectures use plain atomic
operations to set/get the priority value of a scheduler node.  On 32-bit
architectures use an ISR lock.  Using a sequence lock has no real
benefit since it uses atomic read-modify-write operations for both the
read and the write lock.  Simply use a ticket lock instead so that only
one SMP synchronization primitive is used for everything.
---
 cpukit/include/rtems/score/schedulernode.h    | 14 ++--
 .../include/rtems/score/schedulernodeimpl.h   | 64 +++++++++++++------
 .../score/src/schedulerdefaultnodedestroy.c   |  4 +-
 3 files changed, 57 insertions(+), 25 deletions(-)

diff --git a/cpukit/include/rtems/score/schedulernode.h b/cpukit/include/rtems/score/schedulernode.h
index 1dba200dca..e344479718 100644
--- a/cpukit/include/rtems/score/schedulernode.h
+++ b/cpukit/include/rtems/score/schedulernode.h
@@ -28,7 +28,7 @@
 #include <rtems/score/basedefs.h>
 #include <rtems/score/chain.h>
 #include <rtems/score/priority.h>
-#include <rtems/score/smplockseq.h>
+#include <rtems/score/isrlock.h>
 
 /**
  * @addtogroup RTEMSScoreScheduler
@@ -197,14 +197,20 @@ struct Scheduler_Node {
      * least-significant bit which indicates if the thread should be appended
      * (bit set) or prepended (bit cleared) to its priority group, see
      * SCHEDULER_PRIORITY_APPEND().
+     *
+     * @see _Scheduler_Node_get_priority() and _Scheduler_Node_set_priority().
      */
+#if defined(RTEMS_SMP) && CPU_SIZEOF_POINTER == 8
+    Atomic_Ulong value;
+#else
     Priority_Control value;
+#endif
 
-#if defined(RTEMS_SMP)
+#if defined(RTEMS_SMP) && CPU_SIZEOF_POINTER != 8
     /**
-     * @brief Sequence lock to synchronize priority value updates.
+     * @brief The lock protects the priority value.
      */
-    SMP_sequence_lock_Control Lock;
+    ISR_lock_Control Lock;
 #endif
   } Priority;
 };
diff --git a/cpukit/include/rtems/score/schedulernodeimpl.h b/cpukit/include/rtems/score/schedulernodeimpl.h
index 3da29bb37e..3f90d4a6f5 100644
--- a/cpukit/include/rtems/score/schedulernodeimpl.h
+++ b/cpukit/include/rtems/score/schedulernodeimpl.h
@@ -100,13 +100,36 @@ RTEMS_INLINE_ROUTINE void _Scheduler_Node_do_initialize(
   node->Wait.Priority.scheduler = scheduler;
   node->user = the_thread;
   node->idle = NULL;
-  _SMP_sequence_lock_Initialize( &node->Priority.Lock );
+#if CPU_SIZEOF_POINTER != 8
+  _ISR_lock_Initialize( &node->Priority.Lock, "Scheduler Node Priority" );
+#endif
 #else
   (void) scheduler;
   (void) the_thread;
 #endif
 }
 
+/**
+ * @brief Destroys a node.
+ *
+ * @param scheduler is the scheduler of the node.
+ *
+ * @param[in, out] node is the node to destroy.
+ */
+RTEMS_INLINE_ROUTINE void _Scheduler_Node_do_destroy(
+  const struct _Scheduler_Control *scheduler,
+  Scheduler_Node                  *node
+)
+{
+  (void) scheduler;
+
+#if defined(RTEMS_SMP) && CPU_SIZEOF_POINTER != 8
+  _ISR_lock_Destroy( &node->Priority.Lock );
+#else
+  (void) node;
+#endif
+}
+
 /**
  * @brief Gets the scheduler of the node.
  *
@@ -148,17 +171,18 @@ RTEMS_INLINE_ROUTINE Priority_Control _Scheduler_Node_get_priority(
 {
   Priority_Control priority;
 
-#if defined(RTEMS_SMP)
-  unsigned int     seq;
-
-  do {
-    seq = _SMP_sequence_lock_Read_begin( &node->Priority.Lock );
-#endif
-
-    priority = node->Priority.value;
+#if defined(RTEMS_SMP) && CPU_SIZEOF_POINTER == 8
+  priority = _Atomic_Fetch_add_ulong(
+    &node->Priority.value,
+    0,
+    ATOMIC_ORDER_RELAXED
+  );
+#else
+  ISR_lock_Context lock_context;
 
-#if defined(RTEMS_SMP)
-  } while ( _SMP_sequence_lock_Read_retry( &node->Priority.Lock, seq ) );
+  _ISR_lock_Acquire( &node->Priority.Lock, &lock_context );
+  priority = node->Priority.value;
+  _ISR_lock_Release( &node->Priority.Lock, &lock_context );
 #endif
 
   return priority;
@@ -180,16 +204,18 @@ RTEMS_INLINE_ROUTINE void _Scheduler_Node_set_priority(
   Priority_Flags    flags
 )
 {
-#if defined(RTEMS_SMP)
-  unsigned int seq;
-
-  seq = _SMP_sequence_lock_Write_begin( &node->Priority.Lock );
-#endif
+#if defined(RTEMS_SMP) && CPU_SIZEOF_POINTER == 8
+  _Atomic_Store_ulong(
+    &node->Priority.value,
+    new_priority | (Priority_Control) flags,
+    ATOMIC_ORDER_RELAXED
+  );
+#else
+  ISR_lock_Context lock_context;
 
+  _ISR_lock_Acquire( &node->Priority.Lock, &lock_context );
   node->Priority.value = new_priority | ( (Priority_Control) flags );
-
-#if defined(RTEMS_SMP)
-  _SMP_sequence_lock_Write_end( &node->Priority.Lock, seq );
+  _ISR_lock_Release( &node->Priority.Lock, &lock_context );
 #endif
 }
 
diff --git a/cpukit/score/src/schedulerdefaultnodedestroy.c b/cpukit/score/src/schedulerdefaultnodedestroy.c
index 796896d854..33cdfd4c69 100644
--- a/cpukit/score/src/schedulerdefaultnodedestroy.c
+++ b/cpukit/score/src/schedulerdefaultnodedestroy.c
@@ -21,12 +21,12 @@
 #endif
 
 #include <rtems/score/scheduler.h>
+#include <rtems/score/schedulernodeimpl.h>
 
 void _Scheduler_default_Node_destroy(
   const Scheduler_Control *scheduler,
   Scheduler_Node          *node
 )
 {
-  (void) scheduler;
-  (void) node;
+  _Scheduler_Node_do_destroy( scheduler, node );
 }
-- 
2.26.2