diff options
Diffstat (limited to '')
| -rw-r--r-- | ada_user/symmetric_multiprocessing_services.rst | 876 |
1 files changed, 0 insertions, 876 deletions
diff --git a/ada_user/symmetric_multiprocessing_services.rst b/ada_user/symmetric_multiprocessing_services.rst deleted file mode 100644 index 54f84a4..0000000 --- a/ada_user/symmetric_multiprocessing_services.rst +++ /dev/null @@ -1,876 +0,0 @@ -Symmetric Multiprocessing Services -################################## - -Introduction -============ - -The Symmetric Multiprocessing (SMP) support of the RTEMS 4.10.99.0 is -available on - -- ARM, - -- PowerPC, and - -- SPARC. - -It must be explicitly enabled via the ``--enable-smp`` configure command -line option. To enable SMP in the application configuration see `Enable SMP Support for Applications`_. The default -scheduler for SMP applications supports up to 32 processors and is a global -fixed priority scheduler, see also `Configuring Clustered Schedulers`_. For example applications see:file:`testsuites/smptests`. - -*WARNING: The SMP support in RTEMS is work in progress. Before you -start using this RTEMS version for SMP ask on the RTEMS mailing list.* - -This chapter describes the services related to Symmetric Multiprocessing -provided by RTEMS. - -The application level services currently provided are: - -- ``rtems_get_processor_count`` - Get processor count - -- ``rtems_get_current_processor`` - Get current processor index - -- ``rtems_scheduler_ident`` - Get ID of a scheduler - -- ``rtems_scheduler_get_processor_set`` - Get processor set of a scheduler - -- ``rtems_task_get_scheduler`` - Get scheduler of a task - -- ``rtems_task_set_scheduler`` - Set scheduler of a task - -- ``rtems_task_get_affinity`` - Get task processor affinity - -- ``rtems_task_set_affinity`` - Set task processor affinity - -Background -========== - -Uniprocessor versus SMP Parallelism ------------------------------------ - -Uniprocessor systems have long been used in embedded systems. In this hardware -model, there are some system execution characteristics which have long been -taken for granted: - -- one task executes at a time - -- hardware events result in interrupts - -There is no true parallelism. Even when interrupts appear to occur -at the same time, they are processed in largely a serial fashion. -This is true even when the interupt service routines are allowed to -nest. From a tasking viewpoint, it is the responsibility of the real-time -operatimg system to simulate parallelism by switching between tasks. -These task switches occur in response to hardware interrupt events and explicit -application events such as blocking for a resource or delaying. - -With symmetric multiprocessing, the presence of multiple processors -allows for true concurrency and provides for cost-effective performance -improvements. Uniprocessors tend to increase performance by increasing -clock speed and complexity. This tends to lead to hot, power hungry -microprocessors which are poorly suited for many embedded applications. - -The true concurrency is in sharp contrast to the single task and -interrupt model of uniprocessor systems. This results in a fundamental -change to uniprocessor system characteristics listed above. Developers -are faced with a different set of characteristics which, in turn, break -some existing assumptions and result in new challenges. In an SMP system -with N processors, these are the new execution characteristics. - -- N tasks execute in parallel - -- hardware events result in interrupts - -There is true parallelism with a task executing on each processor and -the possibility of interrupts occurring on each processor. Thus in contrast -to their being one task and one interrupt to consider on a uniprocessor, -there are N tasks and potentially N simultaneous interrupts to consider -on an SMP system. - -This increase in hardware complexity and presence of true parallelism -results in the application developer needing to be even more cautious -about mutual exclusion and shared data access than in a uniprocessor -embedded system. Race conditions that never or rarely happened when an -application executed on a uniprocessor system, become much more likely -due to multiple threads executing in parallel. On a uniprocessor system, -these race conditions would only happen when a task switch occurred at -just the wrong moment. Now there are N-1 tasks executing in parallel -all the time and this results in many more opportunities for small -windows in critical sections to be hit. - -Task Affinity -------------- -.. index:: task affinity -.. index:: thread affinity - -RTEMS provides services to manipulate the affinity of a task. Affinity -is used to specify the subset of processors in an SMP system on which -a particular task can execute. - -By default, tasks have an affinity which allows them to execute on any -available processor. - -Task affinity is a possible feature to be supported by SMP-aware -schedulers. However, only a subset of the available schedulers support -affinity. Although the behavior is scheduler specific, if the scheduler -does not support affinity, it is likely to ignore all attempts to set -affinity. - -The scheduler with support for arbitary processor affinities uses a proof of -concept implementation. See https://devel.rtems.org/ticket/2510. - -Task Migration --------------- -.. index:: task migration -.. index:: thread migration - -With more than one processor in the system tasks can migrate from one processor -to another. There are three reasons why tasks migrate in RTEMS. - -- The scheduler changes explicitly via ``rtems_task_set_scheduler()`` or - similar directives. - -- The task resumes execution after a blocking operation. On a priority - based scheduler it will evict the lowest priority task currently assigned to a - processor in the processor set managed by the scheduler instance. - -- The task moves temporarily to another scheduler instance due to locking - protocols like *Migratory Priority Inheritance* or the*Multiprocessor Resource Sharing Protocol*. - -Task migration should be avoided so that the working set of a task can stay on -the most local cache level. - -The current implementation of task migration in RTEMS has some implications -with respect to the interrupt latency. It is crucial to preserve the system -invariant that a task can execute on at most one processor in the system at a -time. This is accomplished with a boolean indicator in the task context. The -processor architecture specific low-level task context switch code will mark -that a task context is no longer executing and waits that the heir context -stopped execution before it restores the heir context and resumes execution of -the heir task. So there is one point in time in which a processor is without a -task. This is essential to avoid cyclic dependencies in case multiple tasks -migrate at once. Otherwise some supervising entity is necessary to prevent -life-locks. Such a global supervisor would lead to scalability problems so -this approach is not used. Currently the thread dispatch is performed with -interrupts disabled. So in case the heir task is currently executing on -another processor then this prolongs the time of disabled interrupts since one -processor has to wait for another processor to make progress. - -It is difficult to avoid this issue with the interrupt latency since interrupts -normally store the context of the interrupted task on its stack. In case a -task is marked as not executing we must not use its task stack to store such an -interrupt context. We cannot use the heir stack before it stopped execution on -another processor. So if we enable interrupts during this transition we have -to provide an alternative task independent stack for this time frame. This -issue needs further investigation. - -Clustered Scheduling --------------------- - -We have clustered scheduling in case the set of processors of a system is -partitioned into non-empty pairwise-disjoint subsets. These subsets are called -clusters. Clusters with a cardinality of one are partitions. Each cluster is -owned by exactly one scheduler instance. - -Clustered scheduling helps to control the worst-case latencies in -multi-processor systems, see *Brandenburg, Björn B.: Scheduling and -Locking in Multiprocessor Real-Time Operating Systems. PhD thesis, 2011.http://www.cs.unc.edu/~bbb/diss/brandenburg-diss.pdf*. The goal is to -reduce the amount of shared state in the system and thus prevention of lock -contention. Modern multi-processor systems tend to have several layers of data -and instruction caches. With clustered scheduling it is possible to honour the -cache topology of a system and thus avoid expensive cache synchronization -traffic. It is easy to implement. The problem is to provide synchronization -primitives for inter-cluster synchronization (more than one cluster is involved -in the synchronization process). In RTEMS there are currently four means -available - -- events, - -- message queues, - -- semaphores using the `Priority Inheritance`_ - protocol (priority boosting), and - -- semaphores using the `Multiprocessor Resource Sharing Protocol`_ (MrsP). - -The clustered scheduling approach enables separation of functions with -real-time requirements and functions that profit from fairness and high -throughput provided the scheduler instances are fully decoupled and adequate -inter-cluster synchronization primitives are used. This is work in progress. - -For the configuration of clustered schedulers see `Configuring Clustered Schedulers`_. - -To set the scheduler of a task see `SCHEDULER_IDENT - Get ID of a scheduler`_ - and `TASK_SET_SCHEDULER - Set scheduler of a task`_. - -Task Priority Queues --------------------- - -Due to the support for clustered scheduling the task priority queues need -special attention. It makes no sense to compare the priority values of two -different scheduler instances. Thus, it is not possible to simply use one -plain priority queue for tasks of different scheduler instances. - -One solution to this problem is to use two levels of queues. The top level -queue provides FIFO ordering and contains priority queues. Each priority queue -is associated with a scheduler instance and contains only tasks of this -scheduler instance. Tasks are enqueued in the priority queue corresponding to -their scheduler instance. In case this priority queue was empty, then it is -appended to the FIFO. To dequeue a task the highest priority task of the first -priority queue in the FIFO is selected. Then the first priority queue is -removed from the FIFO. In case the previously first priority queue is not -empty, then it is appended to the FIFO. So there is FIFO fairness with respect -to the highest priority task of each scheduler instances. See also *Brandenburg, Björn B.: A fully preemptive multiprocessor semaphore protocol for -latency-sensitive real-time applications. In Proceedings of the 25th Euromicro -Conference on Real-Time Systems (ECRTS 2013), pages 292â302, 2013.http://www.mpi-sws.org/~bbb/papers/pdf/ecrts13b.pdf*. - -Such a two level queue may need a considerable amount of memory if fast enqueue -and dequeue operations are desired (depends on the scheduler instance count). -To mitigate this problem an approch of the FreeBSD kernel was implemented in -RTEMS. We have the invariant that a task can be enqueued on at most one task -queue. Thus, we need only as many queues as we have tasks. Each task is -equipped with spare task queue which it can give to an object on demand. The -task queue uses a dedicated memory space independent of the other memory used -for the task itself. In case a task needs to block, then there are two options - -- the object already has task queue, then the task enqueues itself to this - already present queue and the spare task queue of the task is added to a list - of free queues for this object, or - -- otherwise, then the queue of the task is given to the object and the task - enqueues itself to this queue. - -In case the task is dequeued, then there are two options - -- the task is the last task on the queue, then it removes this queue from - the object and reclaims it for its own purpose, or - -- otherwise, then the task removes one queue from the free list of the - object and reclaims it for its own purpose. - -Since there are usually more objects than tasks, this actually reduces the -memory demands. In addition the objects contain only a pointer to the task -queue structure. This helps to hide implementation details and makes it -possible to use self-contained synchronization objects in Newlib and GCC (C++ -and OpenMP run-time support). - -Scheduler Helping Protocol --------------------------- - -The scheduler provides a helping protocol to support locking protocols like*Migratory Priority Inheritance* or the *Multiprocessor Resource -Sharing Protocol*. Each ready task can use at least one scheduler node at a -time to gain access to a processor. Each scheduler node has an owner, a user -and an optional idle task. The owner of a scheduler node is determined a task -creation and never changes during the life time of a scheduler node. The user -of a scheduler node may change due to the scheduler helping protocol. A -scheduler node is in one of the four scheduler help states: - -:dfn:`help yourself` - This scheduler node is solely used by the owner task. This task owns no - resources using a helping protocol and thus does not take part in the scheduler - helping protocol. No help will be provided for other tasks. - -:dfn:`help active owner` - This scheduler node is owned by a task actively owning a resource and can be - used to help out tasks. - In case this scheduler node changes its state from ready to scheduled and the - task executes using another node, then an idle task will be provided as a user - of this node to temporarily execute on behalf of the owner task. Thus lower - priority tasks are denied access to the processors of this scheduler instance. - In case a task actively owning a resource performs a blocking operation, then - an idle task will be used also in case this node is in the scheduled state. - -:dfn:`help active rival` - This scheduler node is owned by a task actively obtaining a resource currently - owned by another task and can be used to help out tasks. - The task owning this node is ready and will give away its processor in case the - task owning the resource asks for help. - -:dfn:`help passive` - This scheduler node is owned by a task obtaining a resource currently owned by - another task and can be used to help out tasks. - The task owning this node is blocked. - -The following scheduler operations return a task in need for help - -- unblock, - -- change priority, - -- yield, and - -- ask for help. - -A task in need for help is a task that encounters a scheduler state change from -scheduled to ready (this is a pre-emption by a higher priority task) or a task -that cannot be scheduled in an unblock operation. Such a task can ask tasks -which depend on resources owned by this task for help. - -In case it is not possible to schedule a task in need for help, then the -scheduler nodes available for the task will be placed into the set of ready -scheduler nodes of the corresponding scheduler instances. Once a state change -from ready to scheduled happens for one of scheduler nodes it will be used to -schedule the task in need for help. - -The ask for help scheduler operation is used to help tasks in need for help -returned by the operations mentioned above. This operation is also used in -case the root of a resource sub-tree owned by a task changes. - -The run-time of the ask for help procedures depend on the size of the resource -tree of the task needing help and other resource trees in case tasks in need -for help are produced during this operation. Thus the worst-case latency in -the system depends on the maximum resource tree size of the application. - -Critical Section Techniques and SMP ------------------------------------ - -As discussed earlier, SMP systems have opportunities for true parallelism -which was not possible on uniprocessor systems. Consequently, multiple -techniques that provided adequate critical sections on uniprocessor -systems are unsafe on SMP systems. In this section, some of these -unsafe techniques will be discussed. - -In general, applications must use proper operating system provided mutual -exclusion mechanisms to ensure correct behavior. This primarily means -the use of binary semaphores or mutexes to implement critical sections. - -Disable Interrupts and Interrupt Locks -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -A low overhead means to ensure mutual exclusion in uni-processor configurations -is to disable interrupts around a critical section. This is commonly used in -device driver code and throughout the operating system core. On SMP -configurations, however, disabling the interrupts on one processor has no -effect on other processors. So, this is insufficient to ensure system wide -mutual exclusion. The macros - -- ``rtems_interrupt_disable()``, - -- ``rtems_interrupt_enable()``, and - -- ``rtems_interrupt_flush()`` - -are disabled on SMP configurations and its use will lead to compiler warnings -and linker errors. In the unlikely case that interrupts must be disabled on -the current processor, then the - -- ``rtems_interrupt_local_disable()``, and - -- ``rtems_interrupt_local_enable()`` - -macros are now available in all configurations. - -Since disabling of interrupts is not enough to ensure system wide mutual -exclusion on SMP, a new low-level synchronization primitive was added - the -interrupt locks. They are a simple API layer on top of the SMP locks used for -low-level synchronization in the operating system core. Currently they are -implemented as a ticket lock. On uni-processor configurations they degenerate -to simple interrupt disable/enable sequences. It is disallowed to acquire a -single interrupt lock in a nested way. This will result in an infinite loop -with interrupts disabled. While converting legacy code to interrupt locks care -must be taken to avoid this situation. -.. code:: c - - void legacy_code_with_interrupt_disable_enable( void ) - { - rtems_interrupt_level level; - rtems_interrupt_disable( level ); - /* Some critical stuff \*/ - rtems_interrupt_enable( level ); - } - RTEMS_INTERRUPT_LOCK_DEFINE( static, lock, "Name" ) - void smp_ready_code_with_interrupt_lock( void ) - { - rtems_interrupt_lock_context lock_context; - rtems_interrupt_lock_acquire( &lock, &lock_context ); - /* Some critical stuff \*/ - rtems_interrupt_lock_release( &lock, &lock_context ); - } - -The ``rtems_interrupt_lock`` structure is empty on uni-processor -configurations. Empty structures have a different size in C -(implementation-defined, zero in case of GCC) and C++ (implementation-defined -non-zero value, one in case of GCC). Thus the``RTEMS_INTERRUPT_LOCK_DECLARE()``, ``RTEMS_INTERRUPT_LOCK_DEFINE()``,``RTEMS_INTERRUPT_LOCK_MEMBER()``, and``RTEMS_INTERRUPT_LOCK_REFERENCE()`` macros are provided to ensure ABI -compatibility. - -Highest Priority Task Assumption -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -On a uniprocessor system, it is safe to assume that when the highest -priority task in an application executes, it will execute without being -preempted until it voluntarily blocks. Interrupts may occur while it is -executing, but there will be no context switch to another task unless -the highest priority task voluntarily initiates it. - -Given the assumption that no other tasks will have their execution -interleaved with the highest priority task, it is possible for this -task to be constructed such that it does not need to acquire a binary -semaphore or mutex for protected access to shared data. - -In an SMP system, it cannot be assumed there will never be a single task -executing. It should be assumed that every processor is executing another -application task. Further, those tasks will be ones which would not have -been executed in a uniprocessor configuration and should be assumed to -have data synchronization conflicts with what was formerly the highest -priority task which executed without conflict. - -Disable Preemption -~~~~~~~~~~~~~~~~~~ - -On a uniprocessor system, disabling preemption in a task is very similar -to making the highest priority task assumption. While preemption is -disabled, no task context switches will occur unless the task initiates -them voluntarily. And, just as with the highest priority task assumption, -there are N-1 processors also running tasks. Thus the assumption that no -other tasks will run while the task has preemption disabled is violated. - -Task Unique Data and SMP ------------------------- - -Per task variables are a service commonly provided by real-time operating -systems for application use. They work by allowing the application -to specify a location in memory (typically a ``void *``) which is -logically added to the context of a task. On each task switch, the -location in memory is stored and each task can have a unique value in -the same memory location. This memory location is directly accessed as a -variable in a program. - -This works well in a uniprocessor environment because there is one task -executing and one memory location containing a task-specific value. But -it is fundamentally broken on an SMP system because there are always N -tasks executing. With only one location in memory, N-1 tasks will not -have the correct value. - -This paradigm for providing task unique data values is fundamentally -broken on SMP systems. - -Classic API Per Task Variables -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -The Classic API provides three directives to support per task variables. These are: - -- ``rtems.task_variable_add`` - Associate per task variable - -- ``rtems.task_variable_get`` - Obtain value of a a per task variable - -- ``rtems.task_variable_delete`` - Remove per task variable - -As task variables are unsafe for use on SMP systems, the use of these services -must be eliminated in all software that is to be used in an SMP environment. -The task variables API is disabled on SMP. Its use will lead to compile-time -and link-time errors. It is recommended that the application developer consider -the use of POSIX Keys or Thread Local Storage (TLS). POSIX Keys are available -in all RTEMS configurations. For the availablity of TLS on a particular -architecture please consult the *RTEMS CPU Architecture Supplement*. - -The only remaining user of task variables in the RTEMS code base is the Ada -support. So basically Ada is not available on RTEMS SMP. - -OpenMP ------- - -OpenMP support for RTEMS is available via the GCC provided libgomp. There is -libgomp support for RTEMS in the POSIX configuration of libgomp since GCC 4.9 -(requires a Newlib snapshot after 2015-03-12). In GCC 6.1 or later (requires a -Newlib snapshot after 2015-07-30 for <sys/lock.h> provided self-contained -synchronization objects) there is a specialized libgomp configuration for RTEMS -which offers a significantly better performance compared to the POSIX -configuration of libgomp. In addition application configurable thread pools -for each scheduler instance are available in GCC 6.1 or later. - -The run-time configuration of libgomp is done via environment variables -documented in the `libgomp -manual <https://gcc.gnu.org/onlinedocs/libgomp/>`_. The environment variables are evaluated in a constructor function -which executes in the context of the first initialization task before the -actual initialization task function is called (just like a global C++ -constructor). To set application specific values, a higher priority -constructor function must be used to set up the environment variables. -.. code:: c - - #include <stdlib.h> - void __attribute__((constructor(1000))) config_libgomp( void ) - { - setenv( "OMP_DISPLAY_ENV", "VERBOSE", 1 ); - setenv( "GOMP_SPINCOUNT", "30000", 1 ); - setenv( "GOMP_RTEMS_THREAD_POOLS", "1$2@SCHD", 1 ); - } - -The environment variable ``GOMP_RTEMS_THREAD_POOLS`` is RTEMS-specific. It -determines the thread pools for each scheduler instance. The format for``GOMP_RTEMS_THREAD_POOLS`` is a list of optional``<thread-pool-count>[$<priority>]@<scheduler-name>`` configurations -separated by ``:`` where: - -- ``<thread-pool-count>`` is the thread pool count for this scheduler - instance. - -- ``$<priority>`` is an optional priority for the worker threads of a - thread pool according to ``pthread_setschedparam``. In case a priority - value is omitted, then a worker thread will inherit the priority of the OpenMP - master thread that created it. The priority of the worker thread is not - changed by libgomp after creation, even if a new OpenMP master thread using the - worker has a different priority. - -- ``@<scheduler-name>`` is the scheduler instance name according to the - RTEMS application configuration. - -In case no thread pool configuration is specified for a scheduler instance, -then each OpenMP master thread of this scheduler instance will use its own -dynamically allocated thread pool. To limit the worker thread count of the -thread pools, each OpenMP master thread must call ``omp_set_num_threads``. - -Lets suppose we have three scheduler instances ``IO``, ``WRK0``, and``WRK1`` with ``GOMP_RTEMS_THREAD_POOLS`` set to``"1@WRK0:3$4@WRK1"``. Then there are no thread pool restrictions for -scheduler instance ``IO``. In the scheduler instance ``WRK0`` there is -one thread pool available. Since no priority is specified for this scheduler -instance, the worker thread inherits the priority of the OpenMP master thread -that created it. In the scheduler instance ``WRK1`` there are three thread -pools available and their worker threads run at priority four. - -Thread Dispatch Details ------------------------ - -This section gives background information to developers interested in the -interrupt latencies introduced by thread dispatching. A thread dispatch -consists of all work which must be done to stop the currently executing thread -on a processor and hand over this processor to an heir thread. - -On SMP systems, scheduling decisions on one processor must be propagated to -other processors through inter-processor interrupts. So, a thread dispatch -which must be carried out on another processor happens not instantaneous. Thus -several thread dispatch requests might be in the air and it is possible that -some of them may be out of date before the corresponding processor has time to -deal with them. The thread dispatch mechanism uses three per-processor -variables, - -- the executing thread, - -- the heir thread, and - -- an boolean flag indicating if a thread dispatch is necessary or not. - -Updates of the heir thread and the thread dispatch necessary indicator are -synchronized via explicit memory barriers without the use of locks. A thread -can be an heir thread on at most one processor in the system. The thread context -is protected by a TTAS lock embedded in the context to ensure that it is used -on at most one processor at a time. The thread post-switch actions use a -per-processor lock. This implementation turned out to be quite efficient and -no lock contention was observed in the test suite. - -The current implementation of thread dispatching has some implications with -respect to the interrupt latency. It is crucial to preserve the system -invariant that a thread can execute on at most one processor in the system at a -time. This is accomplished with a boolean indicator in the thread context. -The processor architecture specific context switch code will mark that a thread -context is no longer executing and waits that the heir context stopped -execution before it restores the heir context and resumes execution of the heir -thread (the boolean indicator is basically a TTAS lock). So, there is one -point in time in which a processor is without a thread. This is essential to -avoid cyclic dependencies in case multiple threads migrate at once. Otherwise -some supervising entity is necessary to prevent deadlocks. Such a global -supervisor would lead to scalability problems so this approach is not used. -Currently the context switch is performed with interrupts disabled. Thus in -case the heir thread is currently executing on another processor, the time of -disabled interrupts is prolonged since one processor has to wait for another -processor to make progress. - -It is difficult to avoid this issue with the interrupt latency since interrupts -normally store the context of the interrupted thread on its stack. In case a -thread is marked as not executing, we must not use its thread stack to store -such an interrupt context. We cannot use the heir stack before it stopped -execution on another processor. If we enable interrupts during this -transition, then we have to provide an alternative thread independent stack for -interrupts in this time frame. This issue needs further investigation. - -The problematic situation occurs in case we have a thread which executes with -thread dispatching disabled and should execute on another processor (e.g. it is -an heir thread on another processor). In this case the interrupts on this -other processor are disabled until the thread enables thread dispatching and -starts the thread dispatch sequence. The scheduler (an exception is the -scheduler with thread processor affinity support) tries to avoid such a -situation and checks if a new scheduled thread already executes on a processor. -In case the assigned processor differs from the processor on which the thread -already executes and this processor is a member of the processor set managed by -this scheduler instance, it will reassign the processors to keep the already -executing thread in place. Therefore normal scheduler requests will not lead -to such a situation. Explicit thread migration requests, however, can lead to -this situation. Explicit thread migrations may occur due to the scheduler -helping protocol or explicit scheduler instance changes. The situation can -also be provoked by interrupts which suspend and resume threads multiple times -and produce stale asynchronous thread dispatch requests in the system. - -Operations -========== - -Setting Affinity to a Single Processor --------------------------------------- - -On some embedded applications targeting SMP systems, it may be beneficial to -lock individual tasks to specific processors. In this way, one can designate a -processor for I/O tasks, another for computation, etc.. The following -illustrates the code sequence necessary to assign a task an affinity for -processor with index ``processor_index``. -.. code:: c - - #include <rtems.h> - #include <assert.h> - void pin_to_processor(rtems_id task_id, int processor_index) - { - rtems_status_code sc; - cpu_set_t cpuset; - CPU_ZERO(&cpuset); - CPU_SET(processor_index, &cpuset); - sc = rtems_task_set_affinity(task_id, sizeof(cpuset), &cpuset); - assert(sc == RTEMS_SUCCESSFUL); - } - -It is important to note that the ``cpuset`` is not validated until the``rtems.task_set_affinity`` call is made. At that point, -it is validated against the current system configuration. - -Directives -========== - -This section details the symmetric multiprocessing services. A subsection -is dedicated to each of these services and describes the calling sequence, -related constants, usage, and status codes. - -.. COMMENT: rtems_get_processor_count - -GET_PROCESSOR_COUNT - Get processor count ------------------------------------------ - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -The count of processors in the system. - -**DESCRIPTION:** - -On uni-processor configurations a value of one will be returned. - -On SMP configurations this returns the value of a global variable set during -system initialization to indicate the count of utilized processors. The -processor count depends on the physically or virtually available processors and -application configuration. The value will always be less than or equal to the -maximum count of application configured processors. - -**NOTES:** - -None. - -.. COMMENT: rtems_get_current_processor - -GET_CURRENT_PROCESSOR - Get current processor index ---------------------------------------------------- - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -The index of the current processor. - -**DESCRIPTION:** - -On uni-processor configurations a value of zero will be returned. - -On 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. - -.. COMMENT: rtems_scheduler_ident - - -SCHEDULER_IDENT - Get ID of a scheduler ---------------------------------------- - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - successful operation -``RTEMS.INVALID_ADDRESS`` - ``id`` is NULL -``RTEMS.INVALID_NAME`` - invalid scheduler name -``RTEMS.UNSATISFIED`` - - a scheduler with this name exists, but -the processor set of this scheduler is empty - -**DESCRIPTION:** - -Identifies a scheduler by its name. The scheduler name is determined by the -scheduler configuration. See `Configuring Clustered Schedulers`_. - -**NOTES:** - -None. - -.. COMMENT: rtems_scheduler_get_processor_set - -SCHEDULER_GET_PROCESSOR_SET - Get processor set of a scheduler --------------------------------------------------------------- - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - successful operation -``RTEMS.INVALID_ADDRESS`` - ``cpuset`` is NULL -``RTEMS.INVALID_ID`` - invalid scheduler id -``RTEMS.INVALID_NUMBER`` - the affinity set buffer is too small for -set of processors owned by the scheduler - -**DESCRIPTION:** - -Returns the processor set owned by the scheduler in ``cpuset``. A set bit -in the processor set means that this processor is owned by the scheduler and a -cleared bit means the opposite. - -**NOTES:** - -None. - -.. COMMENT: rtems_task_get_scheduler - -TASK_GET_SCHEDULER - Get scheduler of a task --------------------------------------------- - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - successful operation -``RTEMS.INVALID_ADDRESS`` - ``scheduler_id`` is NULL -``RTEMS.INVALID_ID`` - invalid task id - -**DESCRIPTION:** - -Returns the scheduler identifier of a task identified by ``task_id`` in``scheduler_id``. - -**NOTES:** - -None. - -.. COMMENT: rtems_task_set_scheduler - - -TASK_SET_SCHEDULER - Set scheduler of a task --------------------------------------------- - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - successful operation -``RTEMS.INVALID_ID`` - invalid task or scheduler id -``RTEMS.INCORRECT_STATE`` - the task is in the wrong state to -perform a scheduler change - -**DESCRIPTION:** - -Sets the scheduler of a task identified by ``task_id`` to the scheduler -identified by ``scheduler_id``. The scheduler of a task is initialized to -the scheduler of the task that created it. - -**NOTES:** - -None. - -**EXAMPLE:** - -.. code:: c - - #include <rtems.h> - #include <assert.h> - void task(rtems_task_argument arg); - void example(void) - { - rtems_status_code sc; - rtems_id task_id; - rtems_id scheduler_id; - rtems_name scheduler_name; - scheduler_name = rtems_build_name('W', 'O', 'R', 'K'); - sc = rtems_scheduler_ident(scheduler_name, &scheduler_id); - assert(sc == RTEMS_SUCCESSFUL); - sc = rtems_task_create( - rtems_build_name('T', 'A', 'S', 'K'), - 1, - RTEMS_MINIMUM_STACK_SIZE, - RTEMS_DEFAULT_MODES, - RTEMS_DEFAULT_ATTRIBUTES, - &task_id - ); - assert(sc == RTEMS_SUCCESSFUL); - sc = rtems_task_set_scheduler(task_id, scheduler_id); - assert(sc == RTEMS_SUCCESSFUL); - sc = rtems_task_start(task_id, task, 0); - assert(sc == RTEMS_SUCCESSFUL); - } - -.. COMMENT: rtems_task_get_affinity - -TASK_GET_AFFINITY - Get task processor affinity ------------------------------------------------ - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - successful operation -``RTEMS.INVALID_ADDRESS`` - ``cpuset`` is NULL -``RTEMS.INVALID_ID`` - invalid task id -``RTEMS.INVALID_NUMBER`` - the affinity set buffer is too small for -the current processor affinity set of the task - -**DESCRIPTION:** - -Returns the current processor affinity set of the task in ``cpuset``. A set -bit in the affinity set means that the task can execute on this processor and a -cleared bit means the opposite. - -**NOTES:** - -None. - -.. COMMENT: rtems_task_set_affinity - -TASK_SET_AFFINITY - Set task processor affinity ------------------------------------------------ - -**CALLING SEQUENCE:** - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - successful operation -``RTEMS.INVALID_ADDRESS`` - ``cpuset`` is NULL -``RTEMS.INVALID_ID`` - invalid task id -``RTEMS.INVALID_NUMBER`` - invalid processor affinity set - -**DESCRIPTION:** - -Sets the processor affinity set for the task specified by ``cpuset``. A set -bit in the affinity set means that the task can execute on this processor and a -cleared bit means the opposite. - -**NOTES:** - -This function will not change the scheduler of the task. The intersection of -the processor affinity set and the set of processors owned by the scheduler of -the task must be non-empty. It is not an error if the processor affinity set -contains processors that are not part of the set of processors owned by the -scheduler instance of the task. A task will simply not run under normal -circumstances on these processors since the scheduler ignores them. Some -locking protocols may temporarily use processors that are not included in the -processor affinity set of the task. It is also not an error if the processor -affinity set contains processors that are not part of the system. - -.. COMMENT: COPYRIGHT (c) 2011,2015 - -.. COMMENT: Aeroflex Gaisler AB - -.. COMMENT: All rights reserved. - |