From cee82dfb263705aa384420f51b4780e4e1d7490d Mon Sep 17 00:00:00 2001 From: Sebastian Huber Date: Wed, 2 Sep 2015 16:36:56 +0200 Subject: smp: Documentation --- doc/user/smp.t | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'doc/user') diff --git a/doc/user/smp.t b/doc/user/smp.t index 0c3b58021e..12711e5997 100644 --- a/doc/user/smp.t +++ b/doc/user/smp.t @@ -147,6 +147,45 @@ another processor. So if we enable interrupts during this transition we have to provide an alternative task independent stack for this time frame. This issue needs further investigation. +@subsection Clustered Scheduling + +We have clustered scheduling in case the set of processors of a system is +partitioned into non-empty pairwise-disjoint subsets. These subsets are called +clusters. Clusters with a cardinality of one are partitions. Each cluster is +owned by exactly one scheduler instance. + +Clustered scheduling helps to control the worst-case latencies in +multi-processor systems, see @cite{Brandenburg, Björn B.: Scheduling and +Locking in Multiprocessor Real-Time Operating Systems. PhD thesis, 2011. +@uref{http://www.cs.unc.edu/~bbb/diss/brandenburg-diss.pdf}}. The goal is to +reduce the amount of shared state in the system and thus prevention of lock +contention. Modern multi-processor systems tend to have several layers of data +and instruction caches. With clustered scheduling it is possible to honour the +cache topology of a system and thus avoid expensive cache synchronization +traffic. It is easy to implement. The problem is to provide synchronization +primitives for inter-cluster synchronization (more than one cluster is involved +in the synchronization process). In RTEMS there are currently three means +available + +@itemize @bullet +@item events, +@item message queues, and +@item semaphores using the @ref{Semaphore Manager Multiprocessor Resource +Sharing Protocol} (MrsP). +@end itemize + +The clustered scheduling approach enables separation of functions with +real-time requirements and functions that profit from fairness and high +throughput provided the scheduler instances are fully decoupled and adequate +inter-cluster synchronization primitives are used. This is work in progress. + +For the configuration of clustered schedulers see @ref{Configuring a System +Configuring Clustered Schedulers}. + +To set the scheduler of a task see @ref{Symmetric Multiprocessing Services +SCHEDULER_IDENT - Get ID of a scheduler} and @ref{Symmetric Multiprocessing +Services TASK_SET_SCHEDULER - Set scheduler of a task}. + @subsection Scheduler Helping Protocol The scheduler provides a helping protocol to support locking protocols like -- cgit v1.2.3