CFS scheduler: documentation about scheduling policies
The documentation about the CFS scheduler is scarse when it comes to scheduling policies. This patch adds a chapter about the scheduling policies it supports. Peter Zijlstra provided most of the information for it in http://marc.info/?l=linux-kernel&m=122210038326356&w=2 Signed-off-by: Martin Steigerwald <ms@teamix.de> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -114,7 +114,31 @@ result.
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5. SCHEDULING CLASSES
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5. Scheduling policies
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CFS implements three scheduling policies:
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- SCHED_NORMAL (traditionally called SCHED_OTHER): The scheduling
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policy that is used for regular tasks.
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- SCHED_BATCH: Does not preempt nearly as often as regular tasks
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would, thereby allowing tasks to run longer and make better use of
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caches but at the cost of interactivity. This is well suited for
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batch jobs.
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- SCHED_IDLE: This is even weaker than nice 19, but its not a true
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idle timer scheduler in order to avoid to get into priority
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inversion problems which would deadlock the machine.
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SCHED_FIFO/_RR are implemented in sched_rt.c and are as specified by
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POSIX.
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The command chrt from util-linux-ng 2.13.1.1 can set all of these except
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SCHED_IDLE.
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6. SCHEDULING CLASSES
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The new CFS scheduler has been designed in such a way to introduce "Scheduling
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Classes," an extensible hierarchy of scheduler modules. These modules
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@ -179,7 +203,7 @@ This is the (partial) list of the hooks:
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6. GROUP SCHEDULER EXTENSIONS TO CFS
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7. GROUP SCHEDULER EXTENSIONS TO CFS
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Normally, the scheduler operates on individual tasks and strives to provide
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fair CPU time to each task. Sometimes, it may be desirable to group tasks and
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