Messages in this thread | | | Subject | Re: [PATCH 3/3] sched: update blocked load when newly idle | From | Valentin Schneider <> | Date | Wed, 14 Feb 2018 14:40:43 +0000 |
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On 02/13/2018 10:31 AM, Vincent Guittot wrote: > When NEWLY_IDLE load balance is not triggered, we might need to update the > blocked load anyway. We can kick an ilb so an idle CPU will take care of > updating blocked load or we can try to update them locally before entering > idle. In the latter case, we reuse part of the nohz_idle_balance. > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 324 +++++++++++++++++++++++++++++++--------------------- > 1 file changed, 193 insertions(+), 131 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 9183fee..cb1ab5c 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > > [...] > > /* > + * idle_balance is called by schedule() if this_cpu is about to become > + * idle. Attempts to pull tasks from other CPUs. > + */ > +static int idle_balance(struct rq *this_rq, struct rq_flags *rf) > +{ > + unsigned long next_balance = jiffies + HZ; > + int this_cpu = this_rq->cpu; > + struct sched_domain *sd; > + int pulled_task = 0; > + u64 curr_cost = 0; > + > + /* > + * We must set idle_stamp _before_ calling idle_balance(), such that we > + * measure the duration of idle_balance() as idle time. > + */ > + this_rq->idle_stamp = rq_clock(this_rq); > + > + /* > + * Do not pull tasks towards !active CPUs... > + */ > + if (!cpu_active(this_cpu)) > + return 0; > + > + /* > + * This is OK, because current is on_cpu, which avoids it being picked > + * for load-balance and preemption/IRQs are still disabled avoiding > + * further scheduler activity on it and we're being very careful to > + * re-start the picking loop. > + */ > + rq_unpin_lock(this_rq, rf); > + > + if (this_rq->avg_idle < sysctl_sched_migration_cost || > + !this_rq->rd->overload) { > +#ifdef CONFIG_NO_HZ_COMMON > + unsigned long has_blocked = READ_ONCE(nohz.has_blocked); > + unsigned long next_blocked = READ_ONCE(nohz.next_blocked); > +#endif > + rcu_read_lock(); > + sd = rcu_dereference_check_sched_domain(this_rq->sd); > + if (sd) > + update_next_balance(sd, &next_balance); > + rcu_read_unlock(); > + > +#ifdef CONFIG_NO_HZ_COMMON > + /* > + * This CPU doesn't want to be disturbed by scheduler > + * houskeeping
Typo here (houskeeping)
> + */ > + if (!housekeeping_cpu(this_cpu, HK_FLAG_SCHED)) > + goto out; > + > + /* Will wake up very soon. No time for fdoing anything else*/
Typo here (fdoing)
> + if (this_rq->avg_idle < sysctl_sched_migration_cost) > + goto out; > + > + /* Don't need to update blocked load of idle CPUs*/ > + if (!has_blocked || time_after_eq(jiffies, next_blocked)) > + goto out;
My "stats update via NEWLY_IDLE" test case started misbehaving with this version: we skip most NEWLY_IDLE stats updates. AFAICT this is the culprit.
I believe this time check should be time_before(jiffies, next_blocked) (or time_before_eq depending on what you want to guarantee with the jiffy interval stuff).
> + > + raw_spin_unlock(&this_rq->lock); > + /* > + * This CPU is going to be idle and blocked load of idle CPUs > + * need to be updated. Run the ilb locally as it is a good > + * candidate for ilb instead of waking up another idle CPU. > + * Kick an normal ilb if we failed to do the update. > + */ > + if (!_nohz_idle_balance(this_rq, NOHZ_STATS_KICK, CPU_NEWLY_IDLE)) > + kick_ilb(NOHZ_STATS_KICK); > + raw_spin_lock(&this_rq->lock); > +#endif > + goto out; > + } > +
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