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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
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
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
@ -246,6 +254,12 @@ Glossary
This term is an acronym for
`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
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.
@ -366,6 +380,11 @@ Glossary
dispatch is marked as necessary, then the next thread dispatch will make
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
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
@ -632,9 +651,9 @@ Glossary
another task.
priority
A mechanism used to represent the relative importance of an element in a
set of items. RTEMS uses priority to determine which task should
execute.
The priority is a mechanism used to represent the relative importance of an
element in a set of items. RTEMS uses :term:`task priorities <task priority>` to determine
which :term:`task` should execute.
priority boosting
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
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
A term used to describe systems which are characterized by requiring
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
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
The set of processors on which a task is allowed to execute.