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diff --git a/c-user/scheduling-concepts/smp-schedulers.rst b/c-user/scheduling-concepts/smp-schedulers.rst new file mode 100644 index 0000000..cfab04f --- /dev/null +++ b/c-user/scheduling-concepts/smp-schedulers.rst @@ -0,0 +1,69 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +.. Copyright (C) 2011 Petr Benes +.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) + +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. |