Re: [patch] CFS scheduler, -v12

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Ingo Molnar wrote:
i'm pleased to announce release -v12 of the CFS scheduler patchset.

The CFS patch against v2.6.22-rc1, v2.6.21.1 or v2.6.20.10 can be downloaded from the usual place: http://people.redhat.com/mingo/cfs-scheduler/

-v12 fixes the '3D bug' that caused trivial latencies in 3D games: it turns out that the problem was not resulting out of any core quality of CFS, it was caused by 3D userspace growing dependent on the current inefficiency of the vanilla scheduler's sys_sched_yield() implementation, and CFS's "make yield work well" changes broke it.

Even a simple 3D app like glxgears does a sys_sched_yield() for every frame it generates (!) on certain 3D cards, which in essence punishes any scheduler that implements sys_sched_yield() in a sane manner. This interaction of CFS's yield implementation with this user-space bug could be the main reason why some testers reported SD to be handling 3D games better than CFS. (SD uses a yield implementation similar to the vanilla scheduler.)

So i've added a yield workaround to -v12, which makes it work similar to how the vanilla scheduler and SD does it. (Xorg has been notified and this bug should be fixed there too. This took some time to debug because the 3D driver i'm using for testing does not use sys_sched_yield().) The workaround is activated by default so -v12 should work 'out of the box'.

Mike Galbraith has fixed a bug related to nice levels - the fix should make negative nice levels more potent again.

Changes since -v10:

 - nice level calculation fixes (Mike Galbraith)

- load-balancing improvements (this should fix the SMP performance problem reported by Michael Gerdau)

 - remove the sched_sleep_history_max tunable.

 - more debugging fields.

 - various cleanups, fixlets and code reorganization

As usual, any sort of feedback, bugreport, fix and suggestion is more than welcome,

Load balancing appears to be badly broken in this version. When I started 4 hard spinners on my 2 CPU machine one ended up on one CPU and the other 3 on the other CPU and they stayed there.

Peter
--
Peter Williams                                   [email protected]

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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