Hi, Lei
On 06/17/2013 10:21 AM, Lei Wen wrote:
> nr_busy_cpus in sched_group_power structure cannot present the purpose
> for judging below statement:
> "this cpu's scheduler group has multiple busy cpu's exceeding
> the group's power."
>
> But only could tell how many cpus is doing their jobs for currently.
AFAIK, this nr_busy_cpus presents how many cpus in local group are not
idle, the logical here in nohz_kick_needed() is:
if domain cpus share resources and at least 2 cpus in
local group are not idle, prefer to do balance.
And the idea behind is, we catch the timing when there are idle-cpu and
busy-group and task-moving may cost low.
Your change will remove this timing for balance, I think you may need
some test to prove that this patch will make things better.
Regards,
Michael Wang
>
> However, the original purpose to add this logic still looks good.
> So we move this kind of logic to find_new_ilb, so that we could pick
> out peer from our sharing resource domain whenever possible.
>
> Signed-off-by: Lei Wen <[email protected]>
> ---
> kernel/sched/fair.c | 28 ++++++++++++++++++++++------
> 1 file changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c61a614..64f9120 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5368,10 +5368,31 @@ static struct {
> unsigned long next_balance; /* in jiffy units */
> } nohz ____cacheline_aligned;
>
> +/*
> + * Add the heuristic logic to try waking up idle cpu from
> + * those peers who share resources with us, so that the
> + * cost would be brought to minimum.
> + */
> static inline int find_new_ilb(int call_cpu)
> {
> - int ilb = cpumask_first(nohz.idle_cpus_mask);
> + int ilb = nr_cpu_ids;
> + struct sched_domain *sd;
> +
> + rcu_read_lock();
> + for_each_domain(call_cpu, sd) {
> + /* We loop till sched_domain no longer share resource */
> + if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
> + ilb = cpumask_first(nohz.idle_cpus_mask);
> + break;
> + }
>
> + /* else, we would try to pick the idle cpu from peers first */
> + ilb = cpumask_first_and(nohz.idle_cpus_mask,
> + sched_domain_span(sd));
> + if (ilb < nr_cpu_ids)
> + break;
> + }
> + rcu_read_unlock();
> if (ilb < nr_cpu_ids && idle_cpu(ilb))
> return ilb;
>
> @@ -5620,8 +5641,6 @@ end:
> * Current heuristic for kicking the idle load balancer in the presence
> * of an idle cpu is the system.
> * - This rq has more than one task.
> - * - At any scheduler domain level, this cpu's scheduler group has multiple
> - * busy cpu's exceeding the group's power.
> * - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
> * domain span are idle.
> */
> @@ -5659,9 +5678,6 @@ static inline int nohz_kick_needed(struct rq *rq, int
> cpu)
> struct sched_group_power *sgp = sg->sgp;
> int nr_busy = atomic_read(&sgp->nr_busy_cpus);
>
> - if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1)
> - goto need_kick_unlock;
> -
> if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight
> && (cpumask_first_and(nohz.idle_cpus_mask,
> sched_domain_span(sd)) < cpu))
>
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