score: Fix CPU time used by executing threads

The CPU time used of a thread was previously maintained per-processor
mostly during _Thread_Dispatch().  However, on SMP configurations the
actual processor of a thread is difficult to figure out since thread
dispatching is a highly asynchronous process (e.g. via inter-processor
interrupts).  Only the intended processor of a thread is known to the
scheduler easily.  Do the CPU usage accounting during thread heir
updates in the context of the scheduler operations.  Provide the
function _Thread_Get_CPU_time_used() to get the CPU usage of a thread
using proper locks to get a consistent value.

Close #2627.

1 files changed, 11 insertions, 4 deletions

diff --git a/cpukit/score/include/rtems/score/percpu.h b/cpukit/score/include/rtems/score/percpu.h
index 22017889b3..95c93ddf3a 100644
--- a/cpukit/score/include/rtems/score/percpu.h
+++ b/cpukit/score/include/rtems/score/percpu.h
@@ -333,8 +333,17 @@ typedef struct Per_CPU_Control {
    */
   volatile bool dispatch_necessary;
 
-  /** This is the time of the last context switch on this CPU. */
-  Timestamp_Control time_of_last_context_switch;
+  /**
+   * @brief The CPU usage timestamp contains the time point of the last heir
+   * thread change or last CPU usage update of the executing thread of this
+   * processor.
+   *
+   * Protected by the scheduler lock.
+   *
+   * @see _Scheduler_Update_heir(), _Thread_Dispatch_update_heir() and
+   * _Thread_Get_CPU_time_used().
+   */
+  Timestamp_Control cpu_usage_timestamp;
 
   /**
    * @brief Watchdog state for this processor.
@@ -681,8 +690,6 @@ bool _Per_CPU_State_wait_for_non_initial_state(
   _Per_CPU_Get()->interrupt_stack_high
 #define _Thread_Dispatch_necessary \
   _Per_CPU_Get()->dispatch_necessary
-#define _Thread_Time_of_last_context_switch \
-  _Per_CPU_Get()->time_of_last_context_switch
 
 /**
  * @brief Returns the thread control block of the executing thread.