Re: sched: Improve load balancing in the presence of idle CPUs

[Jason Low <jason.low2@hp.com>]

On Thu, 2015-04-02 at 10:17 +0100, Morten Rasmussen wrote:
> On Thu, Apr 02, 2015 at 06:59:07AM +0100, Jason Low wrote:

> > Also, below is an example patch.
> > 
> > (Without the conversion to idle_cpu(), the check for rq->idle_balance
> > would not be accurate anymore)

> I think this should reduce the latency Preeti is seeing and avoid
> unnecessary wake-ups, however, it may not be quite as aggressive in
> spreading tasks quickly. It will stop the chain-of-kicks as soon as the
> balancer cpu has pulled only one task. The source cpu may still be
> having two tasks and other cpus may still have more than two tasks
> running.

Yeah, good point. I'll wait and see if Preeti finds this to improve
scheduling behavior. If this only helps a little though, we can also try
to make it more aggressive in spreading tasks.

> Depending on how bad it is, we could consider kicking another cpu if the
> imbalance is still significant after the balancer cpu has pulled a task.