score: Introduce CPU budget operations

This patch set replaces the CPU budget algorithm enumeration with a set of CPU
budget operations which implement a particular CPU budget algorithm.  This
helps to hide the CPU budget algorithm implementation details from the general
thread handling.  The CPU budget callouts are turned into CPU budget
operations.  This slightly reduces the size of the thread control block.

All schedulers used the default scheduler tick implementation.  The tick
scheduler operation is removed and the CPU budget operations are directly used
in _Watchdog_Tick() if the executing thread uses a CPU budget algorithm.  This
is performance improvement for all threads which do not use a CPU budget
algorithm (default behaviour).

16 files changed, 164 insertions, 143 deletions

diff --git a/cpukit/include/rtems/posix/pthreadimpl.h b/cpukit/include/rtems/posix/pthreadimpl.h
index 723b20e8d2..0dc7d9dac5 100644
--- a/cpukit/include/rtems/posix/pthreadimpl.h
+++ b/cpukit/include/rtems/posix/pthreadimpl.h
@@ -47,7 +47,7 @@ RTEMS_INLINE_ROUTINE void _POSIX_Threads_Sporadic_timer_insert(
   POSIX_API_Control *api
 )
 {
-  the_thread->cpu_time_budget =
+  the_thread->CPU_budget.available =
     _Timespec_To_ticks( &api->Sporadic.sched_ss_init_budget );
 
   _Watchdog_Per_CPU_insert_ticks(
@@ -61,19 +61,12 @@ RTEMS_INLINE_ROUTINE void _POSIX_Threads_Sporadic_timer_insert(
 void _POSIX_Threads_Sporadic_timer( Watchdog_Control *watchdog );
 
 /**
- * @brief POSIX threads sporadic budget callout.
- *
- * This routine handles the sporadic scheduling algorithm.
- *
- * @param[in] the_thread is a pointer to the thread whose budget
- * has been exceeded.
+ * @brief The POSIX threads sporadic budget operations.
  */
-void _POSIX_Threads_Sporadic_budget_callout(
-  Thread_Control *the_thread
-);
+extern const Thread_CPU_budget_operations _POSIX_Threads_Sporadic_budget;
 
 int _POSIX_Thread_Translate_to_sched_policy(
-  Thread_CPU_budget_algorithms budget_algorithm
+  const Thread_CPU_budget_operations *operations
 );
 
 /**
diff --git a/cpukit/include/rtems/rtems/modesimpl.h b/cpukit/include/rtems/rtems/modesimpl.h
index 924e12fbee..8fdab263f1 100644
--- a/cpukit/include/rtems/rtems/modesimpl.h
+++ b/cpukit/include/rtems/rtems/modesimpl.h
@@ -22,6 +22,7 @@
 #include <rtems/score/schedulerimpl.h>
 #include <rtems/score/smpimpl.h>
 #include <rtems/score/threadimpl.h>
+#include <rtems/score/threadcpubudget.h>
 #include <rtems/config.h>
 
 #ifdef __cplusplus
@@ -148,10 +149,11 @@ RTEMS_INLINE_ROUTINE void _Modes_Apply_timeslice_to_thread(
 )
 {
   if ( _Modes_Is_timeslice( mode_set ) ) {
-    the_thread->budget_algorithm = THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE;
-    the_thread->cpu_time_budget = rtems_configuration_get_ticks_per_timeslice();
+    the_thread->CPU_budget.operations = &_Thread_CPU_budget_reset_timeslice;
+    the_thread->CPU_budget.available =
+      rtems_configuration_get_ticks_per_timeslice();
   } else {
-    the_thread->budget_algorithm = THREAD_CPU_BUDGET_ALGORITHM_NONE;
+    the_thread->CPU_budget.operations = NULL;
   }
 }
 
diff --git a/cpukit/include/rtems/score/scheduler.h b/cpukit/include/rtems/score/scheduler.h
index df9477fbeb..ad9d630023 100644
--- a/cpukit/include/rtems/score/scheduler.h
+++ b/cpukit/include/rtems/score/scheduler.h
@@ -217,9 +217,6 @@ typedef struct {
     Thread_queue_Context *
   );
 
-  /** @see _Scheduler_Tick() */
-  void ( *tick )( const Scheduler_Control *, Thread_Control * );
-
   /** @see _Scheduler_Start_idle() */
   void ( *start_idle )(
     const Scheduler_Control *,
@@ -544,20 +541,6 @@ void _Scheduler_default_Cancel_job(
 );
 
 /**
- * @brief Performs tick operations depending on the CPU budget algorithm for
- * each executing thread.
- *
- * This routine is invoked as part of processing each clock tick.
- *
- * @param scheduler The scheduler.
- * @param[in, out] executing An executing thread.
- */
-void _Scheduler_default_Tick(
-  const Scheduler_Control *scheduler,
-  Thread_Control          *executing
-);
-
-/**
  * @brief Starts an idle thread.
  *
  * @param scheduler This parameter is unused.
diff --git a/cpukit/include/rtems/score/schedulercbs.h b/cpukit/include/rtems/score/schedulercbs.h
index 4b7efc8340..8a9a49ccd9 100644
--- a/cpukit/include/rtems/score/schedulercbs.h
+++ b/cpukit/include/rtems/score/schedulercbs.h
@@ -67,7 +67,6 @@ extern "C" {
     _Scheduler_default_Node_destroy, /* node destroy entry point */ \
     _Scheduler_CBS_Release_job,      /* new period of task */ \
     _Scheduler_CBS_Cancel_job,       /* cancel period of task */ \
-    _Scheduler_default_Tick,         /* tick entry point */ \
     _Scheduler_default_Start_idle    /* start idle entry point */ \
     SCHEDULER_DEFAULT_SET_AFFINITY_OPERATION \
   }
@@ -394,15 +393,9 @@ int _Scheduler_CBS_Set_parameters (
 );
 
 /**
- * @brief Invoked when a limited time quantum is exceeded.
- *
- * This routine is invoked when a limited time quantum is exceeded.
- *
- * @param the_thread The thread that exceeded a limited time quantum.
+ * @brief These are the CBS CPU budget operations.
  */
-void _Scheduler_CBS_Budget_callout(
-  Thread_Control *the_thread
-);
+extern const Thread_CPU_budget_operations _Scheduler_CBS_Budget;
 
 /**
  * @brief Initializes a CBS specific scheduler node of @a the_thread.
diff --git a/cpukit/include/rtems/score/scheduleredf.h b/cpukit/include/rtems/score/scheduleredf.h
index 9e643b93eb..258563217f 100644
--- a/cpukit/include/rtems/score/scheduleredf.h
+++ b/cpukit/include/rtems/score/scheduleredf.h
@@ -66,7 +66,6 @@ extern "C" {
     _Scheduler_default_Node_destroy, /* node destroy entry point */ \
     _Scheduler_EDF_Release_job,      /* new period of task */ \
     _Scheduler_EDF_Cancel_job,       /* cancel period of task */ \
-    _Scheduler_default_Tick,         /* tick entry point */ \
     _Scheduler_default_Start_idle    /* start idle entry point */ \
     SCHEDULER_DEFAULT_SET_AFFINITY_OPERATION \
   }
diff --git a/cpukit/include/rtems/score/scheduleredfsmp.h b/cpukit/include/rtems/score/scheduleredfsmp.h
index 1841aa4a7b..85e438e81d 100644
--- a/cpukit/include/rtems/score/scheduleredfsmp.h
+++ b/cpukit/include/rtems/score/scheduleredfsmp.h
@@ -128,7 +128,6 @@ typedef struct {
     _Scheduler_default_Node_destroy, \
     _Scheduler_EDF_Release_job, \
     _Scheduler_EDF_Cancel_job, \
-    _Scheduler_default_Tick, \
     _Scheduler_EDF_SMP_Start_idle, \
     _Scheduler_EDF_SMP_Set_affinity \
   }
diff --git a/cpukit/include/rtems/score/schedulerimpl.h b/cpukit/include/rtems/score/schedulerimpl.h
index 50110ea6e7..2c53c05056 100644
--- a/cpukit/include/rtems/score/schedulerimpl.h
+++ b/cpukit/include/rtems/score/schedulerimpl.h
@@ -600,44 +600,6 @@ RTEMS_INLINE_ROUTINE void _Scheduler_Cancel_job(
 }
 
 /**
- * @brief Scheduler method invoked at each clock tick.
- *
- * This method is invoked at each clock tick to allow the scheduler
- * implementation to perform any activities required.  For the
- * scheduler which support standard RTEMS features, this includes
- * time-slicing management.
- *
- * @param cpu The cpu control for the operation.
- */
-RTEMS_INLINE_ROUTINE void _Scheduler_Tick( const Per_CPU_Control *cpu )
-{
-  const Scheduler_Control *scheduler;
-  Thread_Control          *executing;
-
-  scheduler = _Scheduler_Get_by_CPU( cpu );
-
-#if defined(RTEMS_SMP)
-  if ( scheduler == NULL ) {
-    /*
-     * In SMP configurations, processors may be removed/added at runtime
-     * from/to a scheduler.  There may be still clock interrupts on currently
-     * unassigned processors.
-     */
-    return;
-  }
-#endif
-
-  /*
-   * Each online processor has at least an idle thread as the executing thread
-   * even in case it has currently no scheduler assigned.  Clock interrupts on
-   * processors which are not online would be a severe bug of the Clock Driver.
-   */
-  executing = _Per_CPU_Get_executing( cpu );
-  _Assert( executing != NULL );
-  ( *scheduler->Operations.tick )( scheduler, executing );
-}
-
-/**
  * @brief Starts the idle thread for a particular processor.
  *
  * @param scheduler The scheduler instance.
diff --git a/cpukit/include/rtems/score/schedulerpriority.h b/cpukit/include/rtems/score/schedulerpriority.h
index e0991f5e31..1ddbb4a8cc 100644
--- a/cpukit/include/rtems/score/schedulerpriority.h
+++ b/cpukit/include/rtems/score/schedulerpriority.h
@@ -57,7 +57,6 @@ extern "C" {
     _Scheduler_default_Node_destroy,      /* node destroy entry point */ \
     _Scheduler_default_Release_job,       /* new period of task */ \
     _Scheduler_default_Cancel_job,        /* cancel period of task */ \
-    _Scheduler_default_Tick,              /* tick entry point */ \
     _Scheduler_default_Start_idle         /* start idle entry point */ \
     SCHEDULER_DEFAULT_SET_AFFINITY_OPERATION \
   }
diff --git a/cpukit/include/rtems/score/schedulerpriorityaffinitysmp.h b/cpukit/include/rtems/score/schedulerpriorityaffinitysmp.h
index 1b660fa296..e997e81128 100644
--- a/cpukit/include/rtems/score/schedulerpriorityaffinitysmp.h
+++ b/cpukit/include/rtems/score/schedulerpriorityaffinitysmp.h
@@ -73,7 +73,6 @@ extern "C" {
     _Scheduler_default_Node_destroy, \
     _Scheduler_default_Release_job, \
     _Scheduler_default_Cancel_job, \
-    _Scheduler_default_Tick, \
     _Scheduler_SMP_Start_idle, \
     _Scheduler_priority_affinity_SMP_Set_affinity \
   }
diff --git a/cpukit/include/rtems/score/schedulerprioritysmp.h b/cpukit/include/rtems/score/schedulerprioritysmp.h
index 56f4aa5a5b..fe314fb05b 100644
--- a/cpukit/include/rtems/score/schedulerprioritysmp.h
+++ b/cpukit/include/rtems/score/schedulerprioritysmp.h
@@ -101,7 +101,6 @@ typedef struct {
     _Scheduler_default_Node_destroy, \
     _Scheduler_default_Release_job, \
     _Scheduler_default_Cancel_job, \
-    _Scheduler_default_Tick, \
     _Scheduler_SMP_Start_idle \
     SCHEDULER_DEFAULT_SET_AFFINITY_OPERATION \
   }
diff --git a/cpukit/include/rtems/score/schedulersimple.h b/cpukit/include/rtems/score/schedulersimple.h
index 63310e9796..15471a6498 100644
--- a/cpukit/include/rtems/score/schedulersimple.h
+++ b/cpukit/include/rtems/score/schedulersimple.h
@@ -56,7 +56,6 @@ extern "C" {
     _Scheduler_default_Node_destroy,      /* node destroy entry point */ \
     _Scheduler_default_Release_job,       /* new period of task */ \
     _Scheduler_default_Cancel_job,        /* cancel period of task */ \
-    _Scheduler_default_Tick,              /* tick entry point */ \
     _Scheduler_default_Start_idle         /* start idle entry point */ \
     SCHEDULER_DEFAULT_SET_AFFINITY_OPERATION \
   }
diff --git a/cpukit/include/rtems/score/schedulersimplesmp.h b/cpukit/include/rtems/score/schedulersimplesmp.h
index 961e60ae73..c8394781c9 100644
--- a/cpukit/include/rtems/score/schedulersimplesmp.h
+++ b/cpukit/include/rtems/score/schedulersimplesmp.h
@@ -83,7 +83,6 @@ typedef struct {
     _Scheduler_default_Node_destroy, \
     _Scheduler_default_Release_job, \
     _Scheduler_default_Cancel_job, \
-    _Scheduler_default_Tick, \
     _Scheduler_SMP_Start_idle \
     SCHEDULER_DEFAULT_SET_AFFINITY_OPERATION \
   }
diff --git a/cpukit/include/rtems/score/schedulerstrongapa.h b/cpukit/include/rtems/score/schedulerstrongapa.h
index a3a19d80c1..bbded1b493 100644
--- a/cpukit/include/rtems/score/schedulerstrongapa.h
+++ b/cpukit/include/rtems/score/schedulerstrongapa.h
@@ -169,7 +169,6 @@ typedef struct {
     _Scheduler_default_Node_destroy, \
     _Scheduler_default_Release_job, \
     _Scheduler_default_Cancel_job, \
-    _Scheduler_default_Tick, \
     _Scheduler_strong_APA_Start_idle, \
     _Scheduler_strong_APA_Set_affinity \
   }
diff --git a/cpukit/include/rtems/score/thread.h b/cpukit/include/rtems/score/thread.h
index aff2f58d77..4c8a97c0f7 100644
--- a/cpukit/include/rtems/score/thread.h
+++ b/cpukit/include/rtems/score/thread.h
@@ -76,14 +76,6 @@ extern "C" {
  *@{
  */
 
-#define RTEMS_SCORE_THREAD_ENABLE_EXHAUST_TIMESLICE
-
-/*
- * With the addition of the Constant Block Scheduler (CBS),
- * this feature is needed even when POSIX is disabled.
- */
-#define RTEMS_SCORE_THREAD_ENABLE_SCHEDULER_CALLOUT
-
 #if defined(RTEMS_DEBUG)
 #define RTEMS_SCORE_THREAD_ENABLE_RESOURCE_COUNT
 #endif
@@ -148,27 +140,47 @@ typedef struct {
 } Thread_Entry_information;
 
 /**
- *  The following lists the algorithms used to manage the thread cpu budget.
- *
- *  Reset Timeslice:   At each context switch, reset the time quantum.
- *  Exhaust Timeslice: Only reset the quantum once it is consumed.
- *  Callout:           Execute routine when budget is consumed.
+ * @brief This structure contains operations which manage the CPU budget of a
+ *   thread.
  */
-typedef enum {
-  THREAD_CPU_BUDGET_ALGORITHM_NONE,
-  THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE,
-  #if defined(RTEMS_SCORE_THREAD_ENABLE_EXHAUST_TIMESLICE)
-    THREAD_CPU_BUDGET_ALGORITHM_EXHAUST_TIMESLICE,
-  #endif
-  #if defined(RTEMS_SCORE_THREAD_ENABLE_SCHEDULER_CALLOUT)
-    THREAD_CPU_BUDGET_ALGORITHM_CALLOUT
-  #endif
-}  Thread_CPU_budget_algorithms;
+typedef struct {
+  /**
+   * @brief This operation is called at each clock tick for the executing
+   *   thread.
+   */
+  void ( *at_tick )( Thread_Control * );
 
-/**  This defines thes the entry point for the thread specific timeslice
- *   budget management algorithm.
+  /**
+   * @brief This operation is called right before a context switch to the
+   *   thread is performed.
+   */
+  void ( *at_context_switch )( Thread_Control * );
+
+  /**
+   * @brief This operation is called to initialize the CPU budget of the
+   *   thread.
+   */
+  void ( *initialize )( Thread_Control * );
+} Thread_CPU_budget_operations;
+
+/**
+ * @brief This structure is used to control the CPU budget of a thread.
  */
-typedef void (*Thread_CPU_budget_algorithm_callout )( Thread_Control * );
+typedef struct {
+  /**
+   * @brief If this member is not NULL, then it references the CPU budget
+   *   operations used to manage the CPU budget of the thread, otherwise it is
+   *   NULL.
+   */
+  const Thread_CPU_budget_operations *operations;
+
+  /**
+   * @brief This member contains the count of the time quantum that this thread
+   *   is allowed to consume until an action takes place defined by the CPU
+   *   budget operations.
+   */
+  uint32_t available;
+} Thread_CPU_budget_control;
 
 /**
  *  The following structure contains the information which defines
@@ -182,12 +194,13 @@ typedef struct {
     * it started.
     */
   bool                                 is_preemptible;
-  /** This field indicates the CPU budget algorith. */
-  Thread_CPU_budget_algorithms         budget_algorithm;
-  /** This field is the routine to invoke when the CPU allotment is
-   *  consumed.
+
+  /**
+   * @brief This member may provide the CPU budget operations activated when a
+   *   thread is initialized before it is started or restarted.
    */
-  Thread_CPU_budget_algorithm_callout  budget_callout;
+  const Thread_CPU_budget_operations *cpu_budget_operations;
+
   /** This field is the initial ISR disable level of this thread. */
   uint32_t                             isr_level;
   /** This field is the initial priority. */
@@ -772,9 +785,7 @@ struct _Thread_Control {
    * the following fields
    *
    * - RTEMS_API_Control::Signal,
-   * - Thread_Control::budget_algorithm,
-   * - Thread_Control::budget_callout,
-   * - Thread_Control::cpu_time_budget,
+   * - Thread_Control::CPU_budget,
    * - Thread_Control::current_state,
    * - Thread_Control::Post_switch_actions,
    * - Thread_Control::Scheduler::control, and
@@ -841,18 +852,11 @@ struct _Thread_Control {
    */
   bool was_created_with_inherited_scheduler;
 
-  /** This field is the length of the time quantum that this thread is
-   *  allowed to consume.  The algorithm used to manage limits on CPU usage
-   *  is specified by budget_algorithm.
-   */
-  uint32_t                              cpu_time_budget;
-  /** This field is the algorithm used to manage this thread's time
-   *  quantum.  The algorithm may be specified as none which case,
-   *  no limit is in place.
+  /**
+   * @brief This member contains the CPU budget control used to manage the CPU
+   *   budget of the thread.
    */
-  Thread_CPU_budget_algorithms          budget_algorithm;
-  /** This field is the method invoked with the budgeted time is consumed. */
-  Thread_CPU_budget_algorithm_callout   budget_callout;
+  Thread_CPU_budget_control CPU_budget;
 
   /**
    * @brief This member contains the amount of CPU time consumed by this thread
diff --git a/cpukit/include/rtems/score/threadcpubudget.h b/cpukit/include/rtems/score/threadcpubudget.h
new file mode 100644
index 0000000000..bcbaa11bdb
--- /dev/null
+++ b/cpukit/include/rtems/score/threadcpubudget.h
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+
+/**
+ * @file
+ *
+ * @ingroup RTEMSScoreThread
+ *
+ * @brief This header file provides interfaces used to implement the CPU budget
+ *   management of threads.
+ */
+
+/*
+ * Copyright (C) 2021 embedded brains GmbH (http://www.embedded-brains.de)
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _RTEMS_SCORE_THREADCPUBUDGET_H
+#define _RTEMS_SCORE_THREADCPUBUDGET_H
+
+#include <rtems/score/thread.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @addtogroup RTEMSScoreThread
+ *
+ * @{
+ */
+
+/**
+ * @brief Does nothing.
+ *
+ * @param the_thread is an unused parameter.
+ */
+void _Thread_CPU_budget_do_nothing( Thread_Control *the_thread );
+
+/**
+ * @brief Sets the available CPU budget of the thread to the configured clock
+ *   ticks per timeslice.
+ *
+ * @param the_thread is the thread to set the available CPU budget.
+ */
+void _Thread_CPU_budget_set_to_ticks_per_timeslice(
+  Thread_Control *the_thread
+);
+
+/**
+ * @brief Consumes one time quantum of the available CPU budget of the thread
+ *   and yields the thread if the available CPU budget is fully consumed.
+ *
+ * While the thread enabled the non-preemptive mode or is not ready, no time
+ * quantum is consumed.
+ *
+ * @param the_thread is the thread to operate on.
+ */
+void _Thread_CPU_budget_consume_and_yield( Thread_Control *the_thread );
+
+/**
+ * @brief These CPU budget operations allocate timeslices to the thread.
+ *
+ * The timeslice is not reset at a context switch to the thread.  Once a
+ * timeslice is consumed, the thread yields.
+ */
+extern const Thread_CPU_budget_operations _Thread_CPU_budget_exhaust_timeslice;
+
+/**
+ * @brief These CPU budget operations allocate timeslices to the thread.
+ *
+ * The timeslice is reset at a context switch to the thread.  Once a timeslice
+ * is consumed, the thread yields.
+ */
+extern const Thread_CPU_budget_operations _Thread_CPU_budget_reset_timeslice;
+
+/** @} */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTEMS_SCORE_THREADCPUBUDGET_H */
diff --git a/cpukit/include/rtems/score/threadimpl.h b/cpukit/include/rtems/score/threadimpl.h
index a983975568..b1ec05f1c4 100644
--- a/cpukit/include/rtems/score/threadimpl.h
+++ b/cpukit/include/rtems/score/threadimpl.h
@@ -176,19 +176,9 @@ typedef struct {
   Priority_Control priority;
 
   /**
-   * @brief The thread's budget algorithm.
+   * @brief The thread's initial CPU budget operations.
    */
-  Thread_CPU_budget_algorithms budget_algorithm;
-
-  /**
-   * @brief The thread's initial budget callout.
-   */
-  Thread_CPU_budget_algorithm_callout budget_callout;
-
-  /**
-   * @brief The thread's initial CPU time budget.
-   */
-  uint32_t cpu_time_budget;
+  const Thread_CPU_budget_operations *cpu_budget_operations;
 
   /**
    * @brief 32-bit unsigned integer name of the object for the thread.