[patch] CFS scheduler, -v12

Ingo Molnar
2007-05-13T15:40:14Z

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,

Ingo