linux-kernel - [patch] CFS (Completely Fair Scheduler), v2

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Date:	Tue, 17 Apr 2007 00:07:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Willy Tarreau <w@....eu>,
	Gene Heskett <gene.heskett@...il.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: [patch] CFS (Completely Fair Scheduler), v2


this is the second release of the CFS (Completely Fair Scheduler) 
patchset, against v2.6.21-rc7:

   http://redhat.com/~mingo/cfs-scheduler/sched-cfs-v2.patch

i'd like to thank everyone for the tremendous amount of feedback and 
testing the v1 patch got - i could hardly keep up with just reading the 
mails! Some of the stuff people addressed i couldnt implement yet, i 
mostly concentrated on bugs, regressions and debuggability.

there's a fair amount of churn:

   15 files changed, 456 insertions(+), 241 deletions(-)

But it's an encouraging sign that there was no crash bug found in v1, 
all the bugs were related to scheduling-behavior details. The code was 
tested on 3 architectures so far: i686, x86_64 and ia64. Most of the 
code size increase in -v2 is due to debugging helpers, they'll be 
removed later. (The new /proc/sched_debug file can be used to see the 
fine details of CFS scheduling.)

Changes since -v1:

 - make nice levels less starvable. (reported by Willy Tarreau)

 - fixed child-runs first. A /proc/sys/kernel/sched_child_runs_first 
   flag can be used to turn it on/off. (This might fix the Kaffeine bug
   reported by S.Çağlar Onur <)

 - changed SCHED_FAIR back to SCHED_NORMAL (suggested by Con Kolivas)

 - UP build fix. (reported by Gabriel C)

 - timer tick micro-optimization (Dmitry Adamushko)

 - preemption fix: sched_class->check_preempt_curr method to decide 
   whether to preempt after a wakeup (or at a timer tick). (Found via a
   fairness-test-utility written for CFS by Mike Galbraith)

 - start forked children with neutral statistics instead of trying to 
   inherit them from the parent: Willy Tarreau reported that this 
   results in better behavior on extreme workloads, and it also 
   simplifies the code quite nicely. Removed sched_exit() and the 
   ->task_exit() methods.

 - make nice levels independent of the sched_granularity value

 - new /proc/sched_debug file listing runqueue details and the rbtree

 - new SCH-* fields in /proc/<NR>/status to see scheduling details

 - new cpu-hog feature (off by default) and sysctl tunable to set it: 
   /proc/sys/kernel/sched_max_hog_history_ns tunable defaults to
   0 (off). Positive values are meant the maximum 'memory' that the 
   scheduler has of CPU hogs.

 - various code cleanups

 - added more statistics temporarily: sum_exec_runtime, 
   sum_wait_runtime.

 - added -CFS-v2 to EXTRAVERSION

as usual, any sort of feedback, bugreports, fixes and suggestions are 
more than welcome,

	Ingo
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