Changeset 874a5ef in rtems-docs


Ignore:
Timestamp:
Feb 19, 2020, 12:53:53 PM (5 weeks ago)
Author:
Sebastian Huber <sebastian.huber@…>
Branches:
master
Children:
99527a1
Parents:
2c37918
git-author:
Sebastian Huber <sebastian.huber@…> (02/19/20 12:53:53)
git-committer:
Sebastian Huber <sebastian.huber@…> (02/20/20 07:56:29)
Message:

c-user: Clarify CONFIGURE_MAXIMUM_PRIORITY

Update #3875.

File:
1 edited

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  • c-user/configuring_a_system.rst

    r2c37918 r874a5ef  
    619619
    620620DESCRIPTION:
    621    This configuration parameter specified the maximum numeric priority of any
    622    task in the system and one less that the number of priority levels in the
    623    system.
    624 
    625    Reducing the number of priorities in the system reduces the amount of memory
    626    allocated from the RTEMS Workspace.
     621   For the schedulers
     622
     623   * :ref:`SchedulerPriority`, which is the default in uniprocessor
     624     configurations and can be configured through the
     625     :ref:`CONFIGURE_SCHEDULER_PRIORITY` configuration option,
     626
     627   * :ref:`SchedulerSMPPriority` which can be configured through the
     628     :ref:`CONFIGURE_SCHEDULER_PRIORITY_SMP` configuration option, and
     629
     630   * :ref:`SchedulerSMPPriorityAffinity` which can be configured through the
     631     :ref:`CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP` configuration option
     632
     633   this configuration option specifies the maximum numeric priority of any task
     634   for these schedulers and one less that the number of priority levels for
     635   these schedulers.  For all other schedulers provided by RTEMS, this
     636   configuration option has no effect.
    627637
    628638NOTES:
     
    633643   to applications.
    634644
    635    With some schedulers, reducing the number of priorities can reduce the
    636    amount of memory used by the scheduler. For example, the Deterministic
    637    Priority Scheduler (DPS) used by default uses three pointers of storage per
    638    priority level. Reducing the number of priorities from 256 levels to
    639    sixteen (16) can reduce memory usage by about three (3) kilobytes.
     645   Reducing the number of priorities through this configuration option reduces
     646   the amount of memory allocated by the schedulers listed above.  These
     647   schedulers use a chain control structure per priority and this structure
     648   consists of three pointers.  On a 32-bit architecture, the allocated memory
     649   is 12 bytes * (``CONFIGURE_MAXIMUM_PRIORITY`` + 1), e.g. 3072 bytes for 256
     650   priority levels (default), 48 bytes for 4 priority levels
     651   (``CONFIGURE_MAXIMUM_PRIORITY == 3``).
    640652
    641653.. index:: CONFIGURE_MAXIMUM_PROCESSORS
     
    14721484
    14731485RANGE:
    1474     One (1) to CONFIGURE_MAXIMUM_PRIORITY.
     1486    One (1) to the maximum user priority value of the scheduler.
    14751487
    14761488DEFAULT VALUE:
     
    35423554    exactly one.
    35433555
     3556    The memory allocated for this scheduler depends on the
     3557    :ref:`CONFIGURE_MAXIMUM_PRIORITY` configuration option.
     3558
    35443559.. index:: CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP
    35453560
     
    35773592    scheduler for up to 32 processors.
    35783593
     3594    The memory allocated for this scheduler depends on the
     3595    :ref:`CONFIGURE_MAXIMUM_PRIORITY` configuration option.
     3596
    35793597.. index:: CONFIGURE_SCHEDULER_PRIORITY_SMP
    35803598
     
    36103628    <ConfigurationSchedulersClustered>` is present, then it is used as the
    36113629    scheduler for up to 32 processors.
     3630
     3631    The memory allocated for this scheduler depends on the
     3632    :ref:`CONFIGURE_MAXIMUM_PRIORITY` configuration option.
    36123633
    36133634.. index:: CONFIGURE_SCHEDULER_SIMPLE
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