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diff --git a/c-user/scheduling_concepts.rst b/c-user/scheduling_concepts.rst deleted file mode 100644 index 22d39e1..0000000 --- a/c-user/scheduling_concepts.rst +++ /dev/null @@ -1,888 +0,0 @@ -.. SPDX-License-Identifier: CC-BY-SA-4.0 - -.. Copyright (C) 2011 Petr Benes -.. Copyright (C) 2010 Gedare Bloom -.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) - -.. index:: scheduling -.. index:: task scheduling - -.. _SchedulingConcepts: - -Scheduling Concepts -******************* - -Introduction -============ - -The concept of scheduling in real-time systems dictates the ability to provide -immediate response to specific external events, particularly the necessity of -scheduling tasks to run within a specified time limit after the occurrence of -an event. For example, software embedded in life-support systems used to -monitor hospital patients must take instant action if a change in the patient's -status is detected. - -The component of RTEMS responsible for providing this capability is -appropriately called the scheduler. The scheduler's sole purpose is to -allocate the all important resource of processor time to the various tasks -competing for attention. - -The directives provided by the scheduler manager are: - -- rtems_scheduler_ident_ - Get ID of a scheduler - -- rtems_scheduler_ident_by_processor_ - Get ID of a scheduler by processor - -- rtems_scheduler_ident_by_processor_set_ - Get ID of a scheduler by processor set - -- rtems_scheduler_get_maximum_priority_ - Get maximum task priority of a scheduler - -- rtems_scheduler_get_processor_ - Get current processor index - -- rtems_scheduler_get_processor_maximum_ - Get processor maximum - -- rtems_scheduler_get_processor_set_ - Get processor set of a scheduler - -- rtems_scheduler_add_processor_ - Add processor to a scheduler - -- rtems_scheduler_remove_processor_ - Remove processor from a scheduler - -.. index:: scheduling algorithms - -Scheduling Algorithms ---------------------- - -RTEMS provides a plugin framework which allows it to support multiple -scheduling algorithms. RTEMS includes multiple scheduling algorithms and the -user can select which of these they wish to use in their application at -link-time. In addition, the user can implement their own scheduling algorithm -and configure RTEMS to use it. - -Supporting multiple scheduling algorithms gives the end user the option to -select the algorithm which is most appropriate to their use case. Most -real-time operating systems schedule tasks using a priority based algorithm, -possibly with preemption control. The classic RTEMS scheduling algorithm which -was the only algorithm available in RTEMS 4.10 and earlier, is a fixed-priority -scheduling algorithm. This scheduling algoritm is suitable for uniprocessor -(e.g. non-SMP) systems and is known as the *Deterministic Priority -Scheduler*. Unless the user configures another scheduling algorithm, RTEMS -will use this on uniprocessor systems. - -.. index:: priority scheduling - -Priority Scheduling -------------------- - -When using priority based scheduling, RTEMS allocates the processor using a -priority-based, preemptive algorithm augmented to provide round-robin -characteristics within individual priority groups. The goal of this algorithm -is to guarantee that the task which is executing on the processor at any point -in time is the one with the highest priority among all tasks in the ready -state. - -When a task is added to the ready chain, it is placed behind all other tasks of -the same priority. This rule provides a round-robin within priority group -scheduling characteristic. This means that in a group of equal priority tasks, -tasks will execute in the order they become ready or FIFO order. Even though -there are ways to manipulate and adjust task priorities, the most important -rule to remember is: - -.. note:: - - Priority based scheduling algorithms will always select the highest priority - task that is ready to run when allocating the processor to a task. - -Priority scheduling is the most commonly used scheduling algorithm. It should -be used by applications in which multiple tasks contend for CPU time or other -resources and there is a need to ensure certain tasks are given priority over -other tasks. - -There are a few common methods of accomplishing the mechanics of this -algorithm. These ways involve a list or chain of tasks in the ready state. - -- The least efficient method is to randomly place tasks in the ready chain - forcing the scheduler to scan the entire chain to determine which task - receives the processor. - -- A more efficient method is to schedule the task by placing it in the proper - place on the ready chain based on the designated scheduling criteria at the - time it enters the ready state. Thus, when the processor is free, the first - task on the ready chain is allocated the processor. - -- Another mechanism is to maintain a list of FIFOs per priority. When a task - is readied, it is placed on the rear of the FIFO for its priority. This - method is often used with a bitmap to assist in locating which FIFOs have - ready tasks on them. This data structure has :math:`O(1)` insert, extract - and find highest ready run-time complexities. - -- A red-black tree may be used for the ready queue with the priority as the - key. This data structure has :math:`O(log(n))` insert, extract and find - highest ready run-time complexities while :math:`n` is the count of tasks in - the ready queue. - -RTEMS currently includes multiple priority based scheduling algorithms as well -as other algorithms which incorporate deadline. Each algorithm is discussed in -the following sections. - -Uniprocessor Schedulers -======================= - -All uniprocessor schedulers included in RTEMS are priority based. The -processor is allocated to the highest priority task allowed to run. - -.. _SchedulerPriority: - -Deterministic Priority Scheduler --------------------------------- - -This is the scheduler implementation which has always been in RTEMS. After the -4.10 release series, it was factored into pluggable scheduler selection. It -schedules tasks using a priority based algorithm which takes into account -preemption. It is implemented using an array of FIFOs with a FIFO per -priority. It maintains a bitmap which is used to track which priorities have -ready tasks. - -This algorithm is deterministic (e.g. predictable and fixed) in execution time. -This comes at the cost of using slightly over three (3) kilobytes of RAM on a -system configured to support 256 priority levels. - -This scheduler is only aware of a single core. - -.. _SchedulerPrioritySimple: - -Simple Priority Scheduler -------------------------- - -This scheduler implementation has the same behaviour as the Deterministic -Priority Scheduler but uses only one linked list to manage all ready tasks. -When a task is readied, a linear search of that linked list is performed to -determine where to insert the newly readied task. - -This algorithm uses much less RAM than the Deterministic Priority Scheduler but -is *O(n)* where *n* is the number of ready tasks. In a small system with a -small number of tasks, this will not be a performance issue. Reducing RAM -consumption is often critical in small systems which are incapable of -supporting a large number of tasks. - -This scheduler is only aware of a single core. - -.. index:: earliest deadline first scheduling - -.. _SchedulerEDF: - -Earliest Deadline First Scheduler ---------------------------------- - -This is an alternative scheduler in RTEMS for single core applications. The -primary EDF advantage is high total CPU utilization (theoretically up to -100%). It assumes that tasks have priorities equal to deadlines. - -This EDF is initially preemptive, however, individual tasks may be declared -not-preemptive. Deadlines are declared using only Rate Monotonic manager which -goal is to handle periodic behavior. Period is always equal to deadline. All -ready tasks reside in a single ready queue implemented using a red-black tree. - -This implementation of EDF schedules two different types of task priority types -while each task may switch between the two types within its execution. If a -task does have a deadline declared using the Rate Monotonic manager, the task -is deadline-driven and its priority is equal to deadline. On the contrary if a -task does not have any deadline or the deadline is cancelled using the Rate -Monotonic manager, the task is considered a background task with priority equal -to that assigned upon initialization in the same manner as for priority -scheduler. Each background task is of a lower importance than each -deadline-driven one and is scheduled when no deadline-driven task and no higher -priority background task is ready to run. - -Every deadline-driven scheduling algorithm requires means for tasks to claim a -deadline. The Rate Monotonic Manager is responsible for handling periodic -execution. In RTEMS periods are equal to deadlines, thus if a task announces a -period, it has to be finished until the end of this period. The call of -``rtems_rate_monotonic_period`` passes the scheduler the length of oncoming -deadline. Moreover, the ``rtems_rate_monotonic_cancel`` and -``rtems_rate_monotonic_delete`` calls clear the deadlines assigned to the task. - -.. index:: constant bandwidth server scheduling - -.. _SchedulerCBS: - -Constant Bandwidth Server Scheduling (CBS) ------------------------------------------- - -This is an alternative scheduler in RTEMS for single core applications. The -CBS is a budget aware extension of EDF scheduler. The main goal of this -scheduler is to ensure temporal isolation of tasks meaning that a task's -execution in terms of meeting deadlines must not be influenced by other tasks -as if they were run on multiple independent processors. - -Each task can be assigned a server (current implementation supports only one -task per server). The server is characterized by period (deadline) and -computation time (budget). The ratio budget/period yields bandwidth, which is -the fraction of CPU to be reserved by the scheduler for each subsequent period. - -The CBS is equipped with a set of rules applied to tasks attached to servers -ensuring that deadline miss because of another task cannot occur. In case a -task breaks one of the rules, its priority is pulled to background until the -end of its period and then restored again. The rules are: - -- Task cannot exceed its registered budget, - -- Task cannot be unblocked when a ratio between remaining budget and remaining - deadline is higher than declared bandwidth. - -The CBS provides an extensive API. Unlike EDF, the -``rtems_rate_monotonic_period`` does not declare a deadline because it is -carried out using CBS API. This call only announces next period. - -SMP Schedulers -============== - -All SMP schedulers included in RTEMS are priority based. The processors -managed by a scheduler instance are allocated to the highest priority tasks -allowed to run. - -.. _SchedulerSMPEDF: - -Earliest Deadline First SMP Scheduler -------------------------------------- - -This is a job-level fixed-priority scheduler using the Earliest Deadline First -(EDF) method. By convention, the maximum priority level is -:math:`min(INT\_MAX, 2^{62} - 1)` for background tasks. Tasks without an -active deadline are background tasks. In case deadlines are not used, then the -EDF scheduler behaves exactly like a fixed-priority scheduler. The tasks with -an active deadline have a higher priority than the background tasks. This -scheduler supports :ref:`task processor affinities <rtems_task_set_affinity>` -of one-to-one and one-to-all, e.g. a task can execute on exactly one processor -or all processors managed by the scheduler instance. The processor affinity -set of a task must contain all online processors to select the one-to-all -affinity. This is to avoid pathological cases if processors are added/removed -to/from the scheduler instance at run-time. In case the processor affinity set -contains not all online processors, then a one-to-one affinity will be used -selecting the processor with the largest index within the set of processors -currently owned by the scheduler instance. This scheduler algorithm supports -:ref:`thread pinning <ThreadPinning>`. The ready queues use a red-black tree -with the task priority as the key. - -This scheduler algorithm is the default scheduler in SMP configurations if more -than one processor is configured (:ref:`CONFIGURE_MAXIMUM_PROCESSORS -<CONFIGURE_MAXIMUM_PROCESSORS>`). - -.. _SchedulerSMPPriority: - -Deterministic Priority SMP Scheduler ------------------------------------- - -A fixed-priority scheduler which uses a table of chains with one chain per -priority level for the ready tasks. The maximum priority level is -configurable. By default, the maximum priority level is 255 (256 priority -levels). - -.. _SchedulerSMPPrioritySimple: - -Simple Priority SMP Scheduler ------------------------------ - -A fixed-priority scheduler which uses a sorted chain for the ready tasks. By -convention, the maximum priority level is 255. The implementation limit is -actually :math:`2^{63} - 1`. - -.. _SchedulerSMPPriorityAffinity: - -Arbitrary Processor Affinity Priority SMP Scheduler ---------------------------------------------------- - -A fixed-priority scheduler which uses a table of chains with one chain per -priority level for the ready tasks. The maximum priority level is -configurable. By default, the maximum priority level is 255 (256 priority -levels). This scheduler supports arbitrary task processor affinities. The -worst-case run-time complexity of some scheduler operations exceeds -:math:`O(n)` while :math:`n` is the count of ready tasks. - -.. index:: scheduling mechanisms - -Scheduling Modification Mechanisms -================================== - -RTEMS provides four mechanisms which allow the user to alter the task -scheduling decisions: - -- user-selectable task priority level - -- task preemption control - -- task timeslicing control - -- manual round-robin selection - -Each of these methods provides a powerful capability to customize sets of tasks -to satisfy the unique and particular requirements encountered in custom -real-time applications. Although each mechanism operates independently, there -is a precedence relationship which governs the effects of scheduling -modifications. The evaluation order for scheduling characteristics is always -priority, preemption mode, and timeslicing. When reading the descriptions of -timeslicing and manual round-robin it is important to keep in mind that -preemption (if enabled) of a task by higher priority tasks will occur as -required, overriding the other factors presented in the description. - -.. index:: task priority - -Task Priority and Scheduling ----------------------------- - -The most significant task scheduling modification mechanism is the ability for -the user to assign a priority level to each individual task when it is created -and to alter a task's priority at run-time. The maximum priority level depends -on the configured scheduler. A lower priority level means higher priority -(higher importance). The maximum priority level of the default uniprocessor -scheduler is 255. - -.. index:: preemption - -Preemption ----------- - -Another way the user can alter the basic scheduling algorithm is by -manipulating the preemption mode flag (``RTEMS_PREEMPT_MASK``) of individual -tasks. If preemption is disabled for a task (``RTEMS_NO_PREEMPT``), then the -task will not relinquish control of the processor until it terminates, blocks, -or re-enables preemption. Even tasks which become ready to run and possess -higher priority levels will not be allowed to execute. Note that the -preemption setting has no effect on the manner in which a task is scheduled. -It only applies once a task has control of the processor. - -.. index:: timeslicing -.. index:: round robin scheduling - -Timeslicing ------------ - -Timeslicing or round-robin scheduling is an additional method which can be used -to alter the basic scheduling algorithm. Like preemption, timeslicing is -specified on a task by task basis using the timeslicing mode flag -(``RTEMS_TIMESLICE_MASK``). If timeslicing is enabled for a task -(``RTEMS_TIMESLICE``), then RTEMS will limit the amount of time the task can -execute before the processor is allocated to another task. Each tick of the -real-time clock reduces the currently running task's timeslice. When the -execution time equals the timeslice, RTEMS will dispatch another task of the -same priority to execute. If there are no other tasks of the same priority -ready to execute, then the current task is allocated an additional timeslice -and continues to run. Remember that a higher priority task will preempt the -task (unless preemption is disabled) as soon as it is ready to run, even if the -task has not used up its entire timeslice. - -.. index:: manual round robin - -Manual Round-Robin ------------------- - -The final mechanism for altering the RTEMS scheduling algorithm is called -manual round-robin. Manual round-robin is invoked by using -the ``rtems_task_wake_after`` directive with a time interval of -``RTEMS_YIELD_PROCESSOR``. This allows a task to give up the processor and be -immediately returned to the ready chain at the end of its priority group. If -no other tasks of the same priority are ready to run, then the task does not -lose control of the processor. - -.. index:: dispatching - -Dispatching Tasks -================= - -The dispatcher is the RTEMS component responsible for allocating the processor -to a ready task. In order to allocate the processor to one task, it must be -deallocated or retrieved from the task currently using it. This involves a -concept called a context switch. To perform a context switch, the dispatcher -saves the context of the current task and restores the context of the task -which has been allocated to the processor. Saving and restoring a task's -context is the storing/loading of all the essential information about a task to -enable it to continue execution without any effects of the interruption. For -example, the contents of a task's register set must be the same when it is -given the processor as they were when it was taken away. All of the -information that must be saved or restored for a context switch is located -either in the TCB or on the task's stacks. - -Tasks that utilize a numeric coprocessor and are created with the -``RTEMS_FLOATING_POINT`` attribute require additional operations during a -context switch. These additional operations are necessary to save and restore -the floating point context of ``RTEMS_FLOATING_POINT`` tasks. To avoid -unnecessary save and restore operations, the state of the numeric coprocessor -is only saved when a ``RTEMS_FLOATING_POINT`` task is dispatched and that task -was not the last task to utilize the coprocessor. - -.. index:: task state transitions - -Task State Transitions -====================== - -Tasks in an RTEMS system must always be in one of the five allowable task -states. These states are: executing, ready, blocked, dormant, and -non-existent. - -A task occupies the non-existent state before a ``rtems_task_create`` has been -issued on its behalf. A task enters the non-existent state from any other -state in the system when it is deleted with the ``rtems_task_delete`` -directive. While a task occupies this state it does not have a TCB or a task -ID assigned to it; therefore, no other tasks in the system may reference this -task. - -When a task is created via the ``rtems_task_create`` directive it enters the -dormant state. This state is not entered through any other means. Although -the task exists in the system, it cannot actively compete for system resources. -It will remain in the dormant state until it is started via the -``rtems_task_start`` directive, at which time it enters the ready state. The -task is now permitted to be scheduled for the processor and to compete for -other system resources. - -.. figure:: ../images/c_user/states.png - :width: 70% - :align: center - :alt: Task State Transitions - -A task occupies the blocked state whenever it is unable to be scheduled to run. -A running task may block itself or be blocked by other tasks in the system. -The running task blocks itself through voluntary operations that cause the task -to wait. The only way a task can block a task other than itself is with the -``rtems_task_suspend`` directive. A task enters the blocked state due to any -of the following conditions: - -- A task issues a ``rtems_task_suspend`` directive which blocks either itself - or another task in the system. - -- The running task issues a ``rtems_barrier_wait`` directive. - -- The running task issues a ``rtems_message_queue_receive`` directive with the - wait option and the message queue is empty. - -- The running task issues an ``rtems_event_receive`` directive with the wait - option and the currently pending events do not satisfy the request. - -- The running task issues a ``rtems_semaphore_obtain`` directive with the wait - option and the requested semaphore is unavailable. - -- The running task issues a ``rtems_task_wake_after`` directive which blocks - the task for the given time interval. If the time interval specified is - zero, the task yields the processor and remains in the ready state. - -- The running task issues a ``rtems_task_wake_when`` directive which blocks the - task until the requested date and time arrives. - -- The running task issues a ``rtems_rate_monotonic_period`` directive and must - wait for the specified rate monotonic period to conclude. - -- The running task issues a ``rtems_region_get_segment`` directive with the - wait option and there is not an available segment large enough to satisfy the - task's request. - -A blocked task may also be suspended. Therefore, both the suspension and the -blocking condition must be removed before the task becomes ready to run again. - -A task occupies the ready state when it is able to be scheduled to run, but -currently does not have control of the processor. Tasks of the same or higher -priority will yield the processor by either becoming blocked, completing their -timeslice, or being deleted. All tasks with the same priority will execute in -FIFO order. A task enters the ready state due to any of the following -conditions: - -- A running task issues a ``rtems_task_resume`` directive for a task that is - suspended and the task is not blocked waiting on any resource. - -- A running task issues a ``rtems_message_queue_send``, - ``rtems_message_queue_broadcast``, or a ``rtems_message_queue_urgent`` - directive which posts a message to the queue on which the blocked task is - waiting. - -- A running task issues an ``rtems_event_send`` directive which sends an event - condition to a task which is blocked waiting on that event condition. - -- A running task issues a ``rtems_semaphore_release`` directive which releases - the semaphore on which the blocked task is waiting. - -- A timeout interval expires for a task which was blocked by a call to the - ``rtems_task_wake_after`` directive. - -- A timeout period expires for a task which blocked by a call to the - ``rtems_task_wake_when`` directive. - -- A running task issues a ``rtems_region_return_segment`` directive which - releases a segment to the region on which the blocked task is waiting and a - resulting segment is large enough to satisfy the task's request. - -- A rate monotonic period expires for a task which blocked by a call to the - ``rtems_rate_monotonic_period`` directive. - -- A timeout interval expires for a task which was blocked waiting on a message, - event, semaphore, or segment with a timeout specified. - -- A running task issues a directive which deletes a message queue, a semaphore, - or a region on which the blocked task is waiting. - -- A running task issues a ``rtems_task_restart`` directive for the blocked - task. - -- The running task, with its preemption mode enabled, may be made ready by - issuing any of the directives that may unblock a task with a higher priority. - This directive may be issued from the running task itself or from an ISR. A - ready task occupies the executing state when it has control of the CPU. A - task enters the executing state due to any of the following conditions: - -- The task is the highest priority ready task in the system. - -- The running task blocks and the task is next in the scheduling queue. The - task may be of equal priority as in round-robin scheduling or the task may - possess the highest priority of the remaining ready tasks. - -- The running task may reenable its preemption mode and a task exists in the - ready queue that has a higher priority than the running task. - -- The running task lowers its own priority and another task is of higher - priority as a result. - -- The running task raises the priority of a task above its own and the running - task is in preemption mode. - -Directives -========== - -This section details the scheduler manager. A subsection is dedicated to each -of these services and describes the calling sequence, related constants, usage, -and status codes. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_ident: - -SCHEDULER_IDENT - Get ID of a scheduler ---------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_ident( - rtems_name name, - rtems_id *id - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ADDRESS`` - - The ``id`` parameter is ``NULL``. - * - ``RTEMS_INVALID_NAME`` - - Invalid scheduler name. - -DESCRIPTION: - Identifies a scheduler by its name. The scheduler name is determined by - the scheduler configuration. See :ref:`ConfigurationSchedulerTable` - and :ref:`CONFIGURE_SCHEDULER_NAME`. - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_ident_by_processor: - -SCHEDULER_IDENT_BY_PROCESSOR - Get ID of a scheduler by processor ------------------------------------------------------------------ - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_ident_by_processor( - uint32_t cpu_index, - rtems_id *id - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ADDRESS`` - - The ``id`` parameter is ``NULL``. - * - ``RTEMS_INVALID_NAME`` - - Invalid processor index. - * - ``RTEMS_INCORRECT_STATE`` - - The processor index is valid, however, this processor is not owned by - a scheduler. - -DESCRIPTION: - Identifies a scheduler by a processor. - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_ident_by_processor_set: - -SCHEDULER_IDENT_BY_PROCESSOR_SET - Get ID of a scheduler by processor set -------------------------------------------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_ident_by_processor_set( - size_t cpusetsize, - const cpu_set_t *cpuset, - rtems_id *id - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ADDRESS`` - - The ``id`` parameter is ``NULL``. - * - ``RTEMS_INVALID_SIZE`` - - Invalid processor set size. - * - ``RTEMS_INVALID_NAME`` - - The processor set contains no online processor. - * - ``RTEMS_INCORRECT_STATE`` - - The processor set is valid, however, the highest numbered online - processor in the specified processor set is not owned by a scheduler. - -DESCRIPTION: - Identifies a scheduler by a processor set. The scheduler is selected - according to the highest numbered online processor in the specified - processor set. - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_get_maximum_priority: - -SCHEDULER_GET_MAXIMUM_PRIORITY - Get maximum task priority of a scheduler -------------------------------------------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_get_maximum_priority( - rtems_id scheduler_id, - rtems_task_priority *priority - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ID`` - - Invalid scheduler instance identifier. - * - ``RTEMS_INVALID_ADDRESS`` - - The ``priority`` parameter is ``NULL``. - -DESCRIPTION: - Returns the maximum task priority of the specified scheduler instance in - ``priority``. - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_get_processor: - -SCHEDULER_GET_PROCESSOR - Get current processor index ------------------------------------------------------ - -CALLING SEQUENCE: - .. code-block:: c - - uint32_t rtems_scheduler_get_processor( void ); - -DIRECTIVE STATUS CODES: - This directive returns the index of the current processor. - -DESCRIPTION: - In uniprocessor configurations, a value of zero will be returned. - - In SMP configurations, an architecture specific method is used to obtain the - index of the current processor in the system. The set of processor indices - is the range of integers starting with zero up to the processor count minus - one. - - Outside of sections with disabled thread dispatching the current processor - index may change after every instruction since the thread may migrate from - one processor to another. Sections with disabled interrupts are sections - with thread dispatching disabled. - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_get_processor_maximum: - -SCHEDULER_GET_PROCESSOR_MAXIMUM - Get processor maximum -------------------------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - uint32_t rtems_scheduler_get_processor_maximum( void ); - -DIRECTIVE STATUS CODES: - This directive returns the processor maximum supported by the system. - -DESCRIPTION: - In uniprocessor configurations, a value of one will be returned. - - In SMP configurations, this directive returns the minimum of the processors - (physically or virtually) available by the platform and the configured - processor maximum. Not all processors in the range from processor index - zero to the last processor index (which is the processor maximum minus one) - may be configured to be used by a scheduler or online (online processors - have a scheduler assigned). - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_get_processor_set: - -SCHEDULER_GET_PROCESSOR_SET - Get processor set of a scheduler --------------------------------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_get_processor_set( - rtems_id scheduler_id, - size_t cpusetsize, - cpu_set_t *cpuset - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ID`` - - Invalid scheduler instance identifier. - * - ``RTEMS_INVALID_ADDRESS`` - - The ``cpuset`` parameter is ``NULL``. - * - ``RTEMS_INVALID_NUMBER`` - - The processor set buffer is too small for the set of processors owned - by the scheduler instance. - -DESCRIPTION: - Returns the processor set owned by the scheduler instance in ``cpuset``. A - set bit in the processor set means that this processor is owned by the - scheduler instance and a cleared bit means the opposite. - -NOTES: - None. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_add_processor: - -SCHEDULER_ADD_PROCESSOR - Add processor to a scheduler ------------------------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_add_processor( - rtems_id scheduler_id, - uint32_t cpu_index - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ID`` - - Invalid scheduler instance identifier. - * - ``RTEMS_NOT_CONFIGURED`` - - The processor is not configured to be used by the application. - * - ``RTEMS_INCORRECT_STATE`` - - The processor is configured to be used by the application, however, it - is not online. - * - ``RTEMS_RESOURCE_IN_USE`` - - The processor is already assigned to a scheduler instance. - -DESCRIPTION: - Adds a processor to the set of processors owned by the specified scheduler - instance. - -NOTES: - Must be called from task context. This operation obtains and releases the - objects allocator lock. - -.. raw:: latex - - \clearpage - -.. _rtems_scheduler_remove_processor: - -SCHEDULER_REMOVE_PROCESSOR - Remove processor from a scheduler --------------------------------------------------------------- - -CALLING SEQUENCE: - .. code-block:: c - - rtems_status_code rtems_scheduler_remove_processor( - rtems_id scheduler_id, - uint32_t cpu_index - ); - -DIRECTIVE STATUS CODES: - .. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - Successful operation. - * - ``RTEMS_INVALID_ID`` - - Invalid scheduler instance identifier. - * - ``RTEMS_INVALID_NUMBER`` - - The processor is not owned by the specified scheduler instance. - * - ``RTEMS_RESOURCE_IN_USE`` - - The set of processors owned by the specified scheduler instance would - be empty after the processor removal and there exists a non-idle task - that uses this scheduler instance as its home scheduler instance. - * - ``RTEMS_RESOURCE_IN_USE`` - - A task with a restricted processor affinity exists that uses this - scheduler instance as its home scheduler instance and it would be no - longer possible to allocate a processor for this task after the - removal of this processor. - -DESCRIPTION: - Removes a processor from set of processors owned by the specified scheduler - instance. - -NOTES: - Must be called from task context. This operation obtains and releases the - objects allocator lock. Removing a processor from a scheduler is a complex - operation that involves all tasks of the system. |