Documentation: migrate "Effects of Disabling Interrupts or Pre-Emption on Response Latency" from wiki

link: https://cwiki.apache.org/confluence/display/NUTTX/Effects+of+Disabling+Interrupts+or+Pre-Emption+on+Response+Latency

Documentation/implementation/critical_sections.rst

@@ -23,7 +23,7 @@ When we discuss critical sections here we really refer to one of two mechanisms:
 
 The use of either mechanism will always harm real-time performance.
 The effects of critical sections on real-time performance is discussed in
-`Effects of Disabling Interrupts or Pre-Emption on Response Latency <https://cwiki.apache.org/confluence/display/NUTTX/Effects+of+Disabling+Interrupts+or+Pre-Emption+on+Response+Latency>`_ [TODO: move to documentation].
+:doc:`/implementation/preemption_latency`.
 The end result is that a certain amount of **jitter** is added to the real-time response.
 
 Critical sections cannot be avoided within the OS and, as a consequence, a certain

Documentation/implementation/index.rst

@@ -9,3 +9,4 @@ Implementation Details
    processes_vs_tasks.rst
    critical_sections.rst
    interrupt_controls.rst
+   preemption_latency.rst

Documentation/implementation/preemption_latency.rst

@@ -0,0 +1,41 @@
+==================================================================
+Effects of Disabling Interrupts or Pre-Emption on Response Latency
+==================================================================
+
+Rate Monotonic Scheduling
+=========================
+
+**Assumption**
+
+  No resource sharing (processes do not share resources, e.g. a hardware
+  resource, a queue, or any kind of semaphore blocking or non-blocking
+  (busy-waits)).
+
+  Wikipedia “Rate Monotonic Scheduling”
+
+**Real world**
+
+We must protect shared resources with locks of some kind. The most aggressive:
+
+#. Disabling interrupts, and
+#. Disabling pre-emption.
+
+What are the effects of real-time performance when this assumptions is violated?
+
+Normal Interrupt Processing
+---------------------------
+
+.. figure:: normal_interrupt.png
+   :align: center
+
+Effect of Disabling Interrupts
+------------------------------
+
+.. figure:: disabling_interrupts.png
+   :align: center
+
+Effect of Disabling Pre-emption
+-------------------------------
+
+.. figure:: disabling_preemption.png
+   :align: center