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diff --git a/posix_users/scheduler.rst b/posix_users/scheduler.rst new file mode 100644 index 0000000..6c115e4 --- /dev/null +++ b/posix_users/scheduler.rst @@ -0,0 +1,192 @@ +Scheduler Manager +################# + +Introduction +============ + +The scheduler manager ... + +The directives provided by the scheduler manager are: + +- ``sched_get_priority_min`` - Get Minimum Priority Value + +- ``sched_get_priority_max`` - Get Maximum Priority Value + +- ``sched_rr_get_interval`` - Get Timeslicing Quantum + +- ``sched_yield`` - Yield the Processor + +Background +========== + +Priority +-------- + +In the RTEMS implementation of the POSIX API, the priorities range from +the low priority of ``sched_get_priority_min()`` to the highest priority of``sched_get_priority_max()``. Numerically higher values represent higher +priorities. + +Scheduling Policies +------------------- + +The following scheduling policies are available: + +*SCHED_FIFO* + Priority-based, preemptive scheduling with no timeslicing. This is equivalent + to what is called "manual round-robin" scheduling. + +*SCHED_RR* + Priority-based, preemptive scheduling with timeslicing. Time quantums are + maintained on a per-thread basis and are not reset at each context switch. + Thus, a thread which is preempted and subsequently resumes execution will + attempt to complete the unused portion of its time quantum. + +*SCHED_OTHER* + Priority-based, preemptive scheduling with timeslicing. Time quantums are + maintained on a per-thread basis and are reset at each context switch. + +*SCHED_SPORADIC* + Priority-based, preemptive scheduling utilizing three additional parameters: + budget, replenishment period, and low priority. Under this policy, the + thread is allowed to execute for "budget" amount of time before its priority + is lowered to "low priority". At the end of each replenishment period, + the thread resumes its initial priority and has its budget replenished. + +Operations +========== + +There is currently no text in this section. + +Directives +========== + +This section details the scheduler manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +sched_get_priority_min - Get Minimum Priority Value +--------------------------------------------------- +.. index:: sched_get_priority_min +.. index:: get minimum priority value + +**CALLING SEQUENCE:** + +.. code:: c + + #include <sched.h> + int sched_get_priority_min( + int policy + ); + +**STATUS CODES:** + +On error, this routine returns -1 and sets errno to one of the following: + +*EINVAL* + The indicated policy is invalid. + +**DESCRIPTION:** + +This routine return the minimum (numerically and logically lowest) priority +for the specified ``policy``. + +**NOTES:** + +NONE + +sched_get_priority_max - Get Maximum Priority Value +--------------------------------------------------- +.. index:: sched_get_priority_max +.. index:: get maximum priority value + +**CALLING SEQUENCE:** + +.. code:: c + + #include <sched.h> + int sched_get_priority_max( + int policy + ); + +**STATUS CODES:** + +On error, this routine returns -1 and sets errno to one of the following: + +*EINVAL* + The indicated policy is invalid. + +**DESCRIPTION:** + +This routine return the maximum (numerically and logically highest) priority +for the specified ``policy``. + +**NOTES:** + +NONE + +sched_rr_get_interval - Get Timeslicing Quantum +----------------------------------------------- +.. index:: sched_rr_get_interval +.. index:: get timeslicing quantum + +**CALLING SEQUENCE:** + +.. code:: c + + #include <sched.h> + int sched_rr_get_interval( + pid_t pid, + struct timespec \*interval + ); + +**STATUS CODES:** + +On error, this routine returns -1 and sets errno to one of the following: + +*ESRCH* + The indicated process id is invalid. + +*EINVAL* + The specified interval pointer parameter is invalid. + +**DESCRIPTION:** + +This routine returns the length of the timeslice quantum in the``interval`` parameter for the specified ``pid``. + +**NOTES:** + +The ``pid`` argument should be 0 to indicate the calling process. + +sched_yield - Yield the Processor +--------------------------------- +.. index:: sched_yield +.. index:: yield the processor + +**CALLING SEQUENCE:** + +.. code:: c + + #include <sched.h> + int sched_yield( void ); + +**STATUS CODES:** + +This routine always returns zero to indicate success. + +**DESCRIPTION:** + +This call forces the calling thread to yield the processor to another +thread. Normally this is used to implement voluntary round-robin +task scheduling. + +**NOTES:** + +NONE + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + |