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c-user: Add task priority glossary terms

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Sebastian Huber 2021-05-12 13:41:47 +02:00
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c-user/glossary.rst
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@ -194,6 +194,14 @@ Glossary
This term is an acronym for Cathode Ray Tube. Normally used in reference to This term is an acronym for Cathode Ray Tube. Normally used in reference to
the man-machine interface. the man-machine interface.
current priority
The current priority of a :term:`task` is the :term:`task priority` with
respect to the :term:`home scheduler` of the task. It is an aggregation of
the :term:`real priority` and temporary priority adjustments due to locking
protocols, the rate-monotonic period objects on some schedulers such as EDF,
and the :term:`POSIX` sporadic server. The current priority is an
:term:`eligible priority`.
deadline deadline
A fixed time limit by which a task must have completed a set of actions. A fixed time limit by which a task must have completed a set of actions.
Beyond this point, the results are of reduced value and may even be Beyond this point, the results are of reduced value and may even be
@ -246,6 +254,12 @@ Glossary
This term is an acronym for This term is an acronym for
`Executable and Linkable Format <https://en.wikipedia.org/wiki/Executable_and_Linkable_Format>`_. `Executable and Linkable Format <https://en.wikipedia.org/wiki/Executable_and_Linkable_Format>`_.
eligible priority
An eligible priority of a :term:`task` is the :term:`task priority` with
respect to the corresponding :term:`eligible scheduler` of the task. An
eligible priority is either the :term:`current priority` or a
:term:`helping priority` of a task.
eligible scheduler eligible scheduler
An eligible scheduler of a :term:`task` is a :term:`scheduler` which can be An eligible scheduler of a :term:`task` is a :term:`scheduler` which can be
used by the task to allocate a processor for the task. used by the task to allocate a processor for the task.
@ -366,6 +380,11 @@ Glossary
dispatch is marked as necessary, then the next thread dispatch will make dispatch is marked as necessary, then the next thread dispatch will make
the heir task the executing task. the heir task the executing task.
helping priority
A helping priority of a :term:`task` is the :term:`task priority` with
respect to the corresponding :term:`helping scheduler` of the task. A
helping priority is an :term:`eligible priority`.
helping scheduler helping scheduler
A helping scheduler of a :term:`task` is a :term:`scheduler` which is a A helping scheduler of a :term:`task` is a :term:`scheduler` which is a
:term:`eligible scheduler` and which is not the :term:`home scheduler` of :term:`eligible scheduler` and which is not the :term:`home scheduler` of
@ -632,9 +651,9 @@ Glossary
another task. another task.
priority priority
A mechanism used to represent the relative importance of an element in a The priority is a mechanism used to represent the relative importance of an
set of items. RTEMS uses priority to determine which task should element in a set of items. RTEMS uses :term:`task priorities <task priority>` to determine
execute. which :term:`task` should execute.
priority boosting priority boosting
A simple approach to extend the priority inheritance protocol for A simple approach to extend the priority inheritance protocol for
@ -686,6 +705,14 @@ Glossary
decided that other tasks are currently more important. A task that is decided that other tasks are currently more important. A task that is
ready to execute and has a processor assigned is called scheduled. ready to execute and has a processor assigned is called scheduled.
real priority
Each :term:`task` has exactly one real priority. The real priority is
always with respect to the :term:`home scheduler` of a task. It is defined
during task initialization. It may be changed by directives such as
:c:func:`rtems_task_set_priority` and
:c:func:`rtems_task_set_scheduler`. The real priority is the foundation
of the :term:`current priority`.
real-time real-time
A term used to describe systems which are characterized by requiring A term used to describe systems which are characterized by requiring
deterministic response times to external stimuli. The external stimuli deterministic response times to external stimuli. The external stimuli
@ -959,6 +986,14 @@ Glossary
Task migration happens in case a task stops execution on one processor Task migration happens in case a task stops execution on one processor
and resumes execution on another processor. and resumes execution on another processor.
task priority
A task priority of a :term:`task` determines its importance relative to
other tasks. The scheduler use task priorities to determine which
:term:`ready task` gets a processor allocated, see :term:`scheduled task`. The
:term:`eligible priorities <eligible priority>` of a task define the position of the task in a
:term:`wait queue` which uses the priority discipline. Each task has at
least the :term:`real priority`.
task processor affinity task processor affinity
The set of processors on which a task is allowed to execute. The set of processors on which a task is allowed to execute.