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SubjectRe: [RFC] scheduler: improve SMP fairness in CFS
Chris Snook wrote:

> A fraction of *each* CPU, or a fraction of *total* CPU? Per-cpu
> granularity doesn't make anything more fair.

Well, our current solution uses per-cpu weights, because our vendor
couldn't get the load balancer working accurately enough. Having
per-cpu weights and cpu affinity gives acceptable results for the case
where we're currently using it.

If the load balancer is good enough, per-system weights would be fine.
It would have to play nicely with affinity though, in the case where it
makes sense to lock tasks to particular cpus.

> If I have two threads with the same priority, and two CPUs, the
> scheduler will put one on each CPU, and they'll run happily without any
> migration or balancing.

Sure. Now add a third thread. How often do you migrate? Put another
way, over what time quantum do we ensure fairness?

Chris
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