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r: 110718
b: refs/heads/master
c: 1a73ef6
h: refs/heads/master
v: v3
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Martin Steigerwald authored and Ingo Molnar committed Sep 23, 2008
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2 changes: 1 addition & 1 deletion [refs]
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refs/heads/master: 006c75f146e58e080d2b2725a6664f71886e112b
refs/heads/master: 1a73ef6ac3f4b44abc9d1875eb9240d7524a7cf7
28 changes: 26 additions & 2 deletions trunk/Documentation/scheduler/sched-design-CFS.txt
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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
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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
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