Re: [PATCH 2/5] sched: factor out code to should_we_balance()

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2013-03-28 at 16:58 +0900, Joonsoo Kim wrote:
> Now checking that this cpu is appropriate to balance is embedded into
> update_sg_lb_stats() and this checking has no direct relationship to
> this
> function.
> 
> There is not enough reason to place this checking at
> update_sg_lb_stats(),
> except saving one iteration for sched_group_cpus.

Its only one iteration if there's only 2 groups, but there can be more
than 2, take any desktop Intel i7, it will have 4-8 cores, each with
HT; thus the CPU domain will have 4-8 groups.

And note that local_group is always the first group of a domain, so
we'd stop the balance at the first group and avoid touching the other
3-7, avoiding touching cachelines on 6-14 cpus.

So this short-cut does make sense.. its not pretty, granted, but
killing it doesn't seem right.