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authorSebastian Huber <sebastian.huber@embedded-brains.de>2021-09-14 15:58:36 +0200
committerSebastian Huber <sebastian.huber@embedded-brains.de>2021-09-15 07:54:43 +0200
commitc81e148179ef5fea8763bfa12611aa7f1b97582d (patch)
tree1aa036855b166f91765afeab55de5e26d0c5b524 /c-user/glossary.rst
parentc-user: Fix message manager documentation (diff)
downloadrtems-docs-c81e148179ef5fea8763bfa12611aa7f1b97582d.tar.bz2
c-user: Define lower and higher priority
Diffstat (limited to 'c-user/glossary.rst')
-rw-r--r--c-user/glossary.rst37
1 files changed, 32 insertions, 5 deletions
diff --git a/c-user/glossary.rst b/c-user/glossary.rst
index 63876ac..c48625b 100644
--- a/c-user/glossary.rst
+++ b/c-user/glossary.rst
@@ -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.