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SubjectRe: [RFC] scheduler: improve SMP fairness in CFS

* Tong Li <tong.n.li@intel.com> wrote:

> > you need to measure it over longer periods of time. Its not worth
> > balancing for such a thing in any high-frequency manner. (we'd trash
> > the cache constantly migrating tasks back and forth.)
>
> I have some data below, but before that, I'd like to say, at the same
> load balancing rate, my proposed approach would allow us to have
> fairness on the order of seconds. I'm less concerned about trashing
> the cache. The important thing is to have a knob that allow users to
> trade off fairness and performance based on their needs. [...]

such a knob already exists to a certain degree, but i havent tested its
full effects on SMP fairness yet. If you pull my scheduler tree:

git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched.git

and if you enable CONFIG_SCHED_DEBUG, then all the sched-domain
parameters become runtime tunable under /proc/sys/cpu*.

Could you try to increase the cross-CPU rebalancing frequency and see
how it impacts the precision of your measurement? Tune 'min_interval'
and 'max_interval' down to increase the frequency of rebalancing.

Ingo
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