On Tue, Mar 19, 2013 at 03:20:57PM +0100, Peter Zijlstra wrote:
> On Thu, 2013-02-14 at 14:48 +0900, Joonsoo Kim wrote:
> > Commit 88b8dac0 makes load_balance() consider other cpus in its group,
> > regardless of idle type. When we do NEWLY_IDLE balancing, we should not
> > consider it, because a motivation of NEWLY_IDLE balancing is to turn
> > this cpu to non idle state if needed. This is not the case of other cpus.
> > So, change code not to consider other cpus for NEWLY_IDLE balancing.
> >
> > With this patch, assign 'if (pulled_task) this_rq->idle_stamp = 0'
> > in idle_balance() is corrected, because NEWLY_IDLE balancing doesn't
> > consider other cpus. Assigning to 'this_rq->idle_stamp' is now valid.
> >
> > Cc: Srivatsa Vaddagiri <va...@linux.vnet.ibm.com>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo....@lge.com>
>
> Fair enough, good catch.
>
> Acked-by: Peter Zijlstra <a.p.zijls...@chello.nl>
>
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 0c6aaf6..97498f4 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -5016,8 +5016,15 @@ static int load_balance(int this_cpu, struct rq
> > *this_rq,
> > .cpus = cpus,
> > };
> >
> > + /* For NEWLY_IDLE load_balancing, we don't need to consider
> > + * other cpus in our group */
> > + if (idle == CPU_NEWLY_IDLE) {
> > + env.dst_grpmask = NULL;
> > + max_lb_iterations = 0;
>
> Just a small nit; I don't think we'll ever get to evaluate
> max_lb_iterations when !dst_grpmask. So strictly speaking its
> superfluous to touch it.
Okay. In next spin, I will remove it and add a comment here.
Thanks.
>
> > + } else {
> > + max_lb_iterations = cpumask_weight(env.dst_grpmask);
> > + }
> > cpumask_copy(cpus, cpu_active_mask);
> > - max_lb_iterations = cpumask_weight(env.dst_grpmask);
> >
> > schedstat_inc(sd, lb_count[idle]);
> >
>
>
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