Re: SD_SHARE_CPUPOWER breaks scheduler fairness

[Joe Korty]

> On Thu, 2 Jun 2005 04:41, Steve Rotolo wrote:
> > I guess the bottom-line is: given N logical cpus, 1/N of all
> > SCHED_NORMAL tasks may get stuck on a sibling cpu with no chance to
> > run.  All it takes is one spinning SCHED_FIFO task.  Sounds like a bug.
> 
> You're right, and excuse me for missing it. We have to let SCHED_NORMAL tasks 
> run for some period with rt tasks. There shouldn't be any combination of 
> mutually exclusive tasks for siblings.
> 
> I'll work on something.

Wild thought: how about doing this for the sibling ...

	rp->nr_running += SOME_BIG_NUMBER

when a SCHED_FIFO task starts running on some cpu, and
undo the above when the cpu is released.   This fools
the load balancer into _gradually_ moving tasks off the
sibling, when the cpu is hogged by some SCHED_FIFO task,
but should have little effect if a SCHED_FIFO task takes
little cpu time.

Regards,
Joe
--
"Money can buy bandwidth, but latency is forever" -- John Mashey


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