Re: [patch] CFS (Completely Fair Scheduler), v2

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Peter Williams wrote:
William Lee Irwin III wrote:
Ingo Molnar wrote:
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.

On Tue, Apr 17, 2007 at 04:46:57PM +1000, Peter Williams wrote:
Have you considered using rq->raw_weighted_load instead of rq->nr_running in calculating fair_clock? This would take the nice value (or RT priority) of the other tasks into account when determining what's fair.

I suspect you mean (curr->load_weight*delta_exec)/rq->raw_weighted_load
in update_curr().

Or something like that, yes. :-)

Actually, this formula can't be used for the migration thread itself as its load_weight isn't an accurate reflection of its static priority. But as the migration thread is a real time task this probably isn't an issue, right?

If this assumption is correct (i.e. curr is never a real time task) then my earlier caveat re division by zero being possible is invalid because the migration task will never be the only task on the runqueue when this code is called.

I'm also assuming here that (because of its name) curr is already on the runqueue when this code is called. If it isn't the divisor in the above expression should be (rq->raw_weighted_load + curr->load_weight). This would also preclude the possibility of divide by zero.

Peter
--
Peter Williams                                   [email protected]

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