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c-user: Mention thread pinning

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Close #3508.
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Sebastian Huber 2018-09-07 15:47:43 +02:00
parent d90c8137a8
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c-user/symmetric_multiprocessing_services.rst
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@ -809,3 +809,25 @@ RTEMS provides two means for per-processor data:
`<rtems/score/percpudata.h> <https://git.rtems.org/rtems/tree/cpukit/include/rtems/score/percpudata.h>`_. `<rtems/score/percpudata.h> <https://git.rtems.org/rtems/tree/cpukit/include/rtems/score/percpudata.h>`_.
This API is not intended for general application use. Please ask on the This API is not intended for general application use. Please ask on the
development mailing list in case you want to use it. development mailing list in case you want to use it.
Thread Pinning
--------------
Thread pinning ensures that a thread is only dispatched to the processor on
which it is pinned. It may be used to access per-processor data structures in
critical sections with enabled thread dispatching, e.g. a pinned thread is
allowed to block. The `_Thread_Pin()` operation will pin the executing thread
to its current processor. A thread may be pinned recursively, the last unpin
request via `_Thread_Unpin()` revokes the pinning.
Thread pinning should be used only for short critical sections and not all
the time. Thread pinning is a very low overhead operation in case the
thread is not preempted during the pinning. A preemption will result in
scheduler operations to ensure that the thread executes only on its pinned
processor. Thread pinning must be used with care, since it prevents help
through the locking protocols. This makes the :ref:`OMIP <OMIP>` and
:ref:`MrsP <MrsP>` locking protocols ineffective if pinned threads are
involved.
The thread pinning is not intended for general application use. Please ask on
the development mailing list in case you want to use it.