Re: [RFC PATCH v3 3/6] sched: pack small tasks

[Peter Zijlstra]

On Tue, 2013-03-26 at 08:29 -0700, Arjan van de Ven wrote:
> > Isn't this basically related to picking the NO_HZ cpu; if the system
> > isn't fully symmetric with its power gates you want the NO_HZ cpu to be
> > the 'special' cpu. If it is symmetric we really don't care which core
> > is left 'running' and we can even select a new pack cpu from the idle
> > cores once the old one is fully utilized.
> 
> you don't really care much sure, but there's some advantages for sorting "all the way left",
> e.g. to linux cpu 0.
> Some tasks only run there, and interrupts tend to be favored to that cpu as well on x86.

Right, and I suspect all the big-little nonsense will have the little
cores on low numbers as well (is this architected or can a creative
licensee screw us over?)

So find_new_ilb() already does cpumask_first(), so it has a strong
leftmost preference. We just need to make sure it indeed does the right
thing and doesn't have some unintended side effect.

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