Ingo Molnar [interview] released version 19 of his CFS scheduler patchset [story], first released back in April [story]. He noted:

"The biggest user-visible change in -v19 is reworked sleeper fairness: it's similar in behavior to -v18 but works more consistently across nice levels. Fork-happy workloads (like kernel builds) should behave better as well. There are also a handful of speedups: unsigned math, 32-bit speedups, O(1) task pickup, debloating and other micro-optimizations."

Among the other changes found in this latest version of the scheduler patchset, Ingo noted, "merged the group-scheduling CFS-core changes from Srivatsa Vaddagiri [story]. This makes up for the bulk of the changes in -v19 but has no behavioral impact. The final group-fairness enabler patch is now a small and lean add-on patch to CFS."

From: Ingo Molnar [email blocked]
To: 	linux-kernel
Subject: [patch] CFS scheduler, -v19
Date:	Fri, 6 Jul 2007 19:33:19 +0200


i'm pleased to announce release -v19 of the CFS scheduler patchset.

The rolled-up CFS patch against today's -git kernel, v2.6.22-rc7, 
v2.6.22-rc6-mm1, v2.6.21.5 or v2.6.20.14 can be downloaded from the 
usual place:

    http://people.redhat.com/mingo/cfs-scheduler/
 
The biggest user-visible change in -v19 is reworked sleeper fairness: 
it's similar in behavior to -v18 but works more consistently across nice 
levels. Fork-happy workloads (like kernel builds) should behave better 
as well. There are also a handful of speedups: unsigned math, 32-bit 
speedups, O(1) task pickup, debloating and other micro-optimizations.

Changes since -v18:

 - merged the group-scheduling CFS-core changes from Srivatsa Vaddagiri. 
   This makes up for the bulk of the changes in -v19 but has no
   behavioral impact. The final group-fairness enabler patch is now a 
   small and lean add-on patch to CFS.

 - fix the bloat noticed by Andrew. On 32-bit it's now this:

      text    data     bss     dec     hex   filename
     24362    3905      24   28291    6e83   sched.o-rc7
     33015    2538      20   35573    8af5   sched.o-v18
     25805    2426      20   28251    6e5b   sched.o-v19

   so it's a net win compared to vanilla. On 64-bit it's even better:

      text    data     bss     dec     hex   filename
     35732   40314    2168   78214   13186   sched.o.x64-rc7
     41397   37642    2168   81207   13d37   sched.o.x64-v18
     36132   37410    2168   75710   127be   sched.o.x64-v19

   ( and there's also a +1.5K data win per CPU on x32, which is not
     shown here. [+3.0K data win per CPU on x64.] )

 - good number of core code updates, cleanups and streamlining.
   (Mike Galbraith, Srivatsa Vaddagiri, Dmitry Adamushko, me.)

 - use unsigned data types almost everywhere in CFS. This produces 
   faster and smaller code, and simplifies the logic.

 - turn as many 'u64' data types into 'unsigned long' as possible, to 
   reduce the 32-bit footprint and to reduce 64-bit arithmetics.

 - replaced the nr_running based 'sleep fairness' logic with a more 
   robust concept. The end-result is similar in behavior to v18, but 
   negative nice levels are handled much better in this scheme.

 - speedup: O(1) task pickup by Srivatsa Vaddagiri. [sleep/wakeup is
   O(log2(nr_running)).] This gives 5-10% better hackbench 100/500
   results on a 4-way box.

 - fix: set idle->sched_class back to &idle_sched_class in 
   migration_call(). (Dmitry Adamushko)

 - cleanup: use an enum for the sched_feature flags. (suggested by 
   Andrew Morton)

 - cleanup: turn the priority macros into inlines. (suggested by
   Andrew Morton)

 - (other cleanups suggested by Andrew Morton)

 - debug: split out the debugging data into CONFIG_SCHED_DEBUG.
 
As usual, any sort of feedback, bugreport, fix and suggestion is more 
than welcome!
 
	Ingo

• Archive of above thread
• KernelTrap interview with Ingo Molnar