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c-user: Define lower and higher priority

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Sebastian Huber 2021-09-14 15:58:36 +02:00
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c-user/glossary.rst
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@ -394,6 +394,10 @@ Glossary
heterogeneous
A multiprocessor computer system composed of dissimilar processors.
higher priority
A :term:`task` ``H`` has a higher :term:`priority` than a task ``L``, if
task ``H`` is more important than task ``L``.
home scheduler
The home scheduler of a :term:`task` is a :term:`scheduler` which is an
:term:`eligible scheduler` and which is assigned to the task during its
@ -494,6 +498,10 @@ Glossary
A multiprocessor configuration where shared memory is not used for
communication.
lower priority
A :term:`task` ``L`` has a lower :term:`priority` than a task ``H``, if
task ``L`` is less important than task ``H``.
major number
The index of a device driver in the Device Driver Table.
@ -660,8 +668,22 @@ Glossary
priority
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.
element in a set of items.
For example, :term:`RTEMS` uses :term:`task priorities <task priority>` to determine which
:term:`task` should execute on a processor. In RTEMS, priorities are
represented by non-negative integers.
For the Classic :term:`API`, if a numerical priority value ``A`` is greater
than a numerical priority value ``B``, then ``A`` expresses a
:term:`higher priority` than ``B``. If a numerical priority value ``C`` is
less than a numerical priority value ``D``, then ``C`` expresses a
:term:`lower priority` than ``D``.
For the :term:`POSIX` API, if a numerical priority value ``R`` is less than
a numerical priority value ``S``, then ``R`` expresses a lower priority than
``S``. If a numerical priority value ``T`` is greater than a numerical
priority value ``U``, then ``T`` expresses a higher priority than ``U``.
priority boosting
A simple approach to extend the priority inheritance protocol for
@ -995,13 +1017,18 @@ Glossary
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
A task :term:`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 priorities are used in :term:`wait queues <wait queue>` which use the priority
discipline to determine the dequeueing order of tasks.
task processor affinity
The set of processors on which a task is allowed to execute.