lkml.org 
[lkml]   [2011]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [patch 3/6] sched, nohz: sched group, domain aware nohz idle load balancing
    From
    Date
    On Fri, 2011-11-18 at 15:03 -0800, Suresh Siddha wrote:
    > static inline int nohz_kick_needed(struct rq *rq, int cpu)
    > {
    > unsigned long now = jiffies;
    > struct sched_domain *sd;
    >
    > + if (unlikely(idle_cpu(cpu)))
    > + return 0;
    > +
    > /*
    > * We were recently in tickless idle mode. At the first busy tick
    > * after returning from idle, we will update the busy stats.
    > @@ -5120,36 +5047,43 @@ static inline int nohz_kick_needed(struc
    > if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
    > clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
    >
    > + cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
    > + atomic_dec(&nohz.nr_cpus);
    > +
    > for_each_domain(cpu, sd)
    > atomic_inc(&sd->groups->sgp->nr_busy_cpus);
    > }
    >
    > + /*
    > + * None are in tickless mode and hence no need for NOHZ idle load
    > + * balancing.
    > + */
    > + if (likely(!atomic_read(&nohz.nr_cpus)))
    > return 0;
    >
    > + if (time_before(now, nohz.next_balance))
    > return 0;
    >
    > + if (rq->nr_running >= 2)
    > + goto need_kick;
    >
    > + for_each_domain(cpu, sd) {
    > + struct sched_group *sg = sd->groups;
    > + struct sched_group_power *sgp = sg->sgp;
    > + int nr_busy = atomic_read(&sgp->nr_busy_cpus);
    > +
    > + if (nr_busy > 1 && (nr_busy * SCHED_LOAD_SCALE > sgp->power))
    > + goto need_kick;

    This looks wrong, its basically always true for a box with HT.

    sgp->power is a measure of how much compute power this group has, its
    basic form is sg->weight * SCHED_POWER_SCALE and is reduced from there;
    HT siblings get less since they're not as powerful as two actual cores
    and we deduct time spend on RT-tasks and IRQs etc..

    So how does comparing the load of non-nohz cpus to that make sense?

    > +
    > + if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight
    > + && (cpumask_first_and(nohz.idle_cpus_mask,
    > + sched_domain_span(sd)) < cpu))
    > + goto need_kick;
    > }
    > +
    > return 0;
    > +need_kick:
    > + return 1;
    > }


    \
     
     \ /
      Last update: 2011-11-24 12:51    [W:0.024 / U:0.220 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site