linux-kernel - Re: [PATCH] CFS scheduler: documentation about scheduling policies

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Message-Id: <200809231348.50834.ms@teamix.de>
Date:	Tue, 23 Sep 2008 13:48:44 +0200
From:	Martin Steigerwald <ms@...mix.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] CFS scheduler: documentation about scheduling policies

Am Dienstag, 23. September 2008 schrieb Ingo Molnar:
> * Martin Steigerwald <ms@...mix.de> wrote:
> > 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
> >
> > This patch is based on 2.6.27-rc7.
> >
> > Signed-off-by: Martin Steigerwald <ms@...mix.de>
>
> looks good to me - but could you please do the patch against the latest
> scheduler tree, which has already updated this file (and which made your
> patch not apply cleanly):
>
>   http://people.redhat.com/mingo/tip.git/README
>
> also:
> > --- sched-design-CFS.txt-2.6.27-rc7     2008-07-13 23:51:29.000000000
> > +0200 +++ sched-design-CFS.txt        2008-09-23 10:33:01.107393509 +0200
>
> please use -p1 to create patches - or since you've just set up the
> tip/master tracking, do something like:

Okay, lets see how this works out.

---
From a57581d4ec3b13f63920b89c336ac9c93c6cf9f0 Mon Sep 17 00:00:00 2001
From: Martin Steigerwald <ms@...mix.de>
Date: Tue, 23 Sep 2008 13:45:46 +0200
Subject: [PATCH] CFS: 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@...mix.de>
---
 Documentation/scheduler/sched-design-CFS.txt |   28 ++++++++++++++++++++++++-
 1 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/Documentation/scheduler/sched-design-CFS.txt b/Documentation/scheduler/sched-design-CFS.txt
index b2aa856..9d8eb55 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

-- 
Martin Steigerwald - team(ix) GmbH - http://www.teamix.de
gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90

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