From 1a73ef6ac3f4b44abc9d1875eb9240d7524a7cf7 Mon Sep 17 00:00:00 2001 From: Martin Steigerwald Date: Tue, 23 Sep 2008 13:48:44 +0200 Subject: [PATCH] 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 Acked-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- Documentation/scheduler/sched-design-CFS.txt | 28 ++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/Documentation/scheduler/sched-design-CFS.txt b/Documentation/scheduler/sched-design-CFS.txt index b2aa856339a7..9d8eb553884c 100644 --- a/Documentation/scheduler/sched-design-CFS.txt +++ b/Documentation/scheduler/sched-design-CFS.txt @@ -114,7 +114,31 @@ result. -5. SCHEDULING CLASSES +5. Scheduling policies + +CFS implements three scheduling policies: + + - SCHED_NORMAL (traditionally called SCHED_OTHER): The scheduling + policy that is used for regular tasks. + + - SCHED_BATCH: Does not preempt nearly as often as regular tasks + would, thereby allowing tasks to run longer and make better use of + caches but at the cost of interactivity. This is well suited for + batch jobs. + + - SCHED_IDLE: This is even weaker than nice 19, but its not a true + idle timer scheduler in order to avoid to get into priority + inversion problems which would deadlock the machine. + +SCHED_FIFO/_RR are implemented in sched_rt.c and are as specified by +POSIX. + +The command chrt from util-linux-ng 2.13.1.1 can set all of these except +SCHED_IDLE. + + + +6. SCHEDULING CLASSES The new CFS scheduler has been designed in such a way to introduce "Scheduling Classes," an extensible hierarchy of scheduler modules. These modules @@ -179,7 +203,7 @@ This is the (partial) list of the hooks: -6. GROUP SCHEDULER EXTENSIONS TO CFS +7. GROUP SCHEDULER EXTENSIONS TO CFS Normally, the scheduler operates on individual tasks and strives to provide fair CPU time to each task. Sometimes, it may be desirable to group tasks and