Messages in this thread | | | Date | Sat, 30 Aug 2014 23:20:56 +0530 | From | Preeti U Murthy <> | Subject | Re: [PATCH v5 08/12] sched: move cfs task on a CPU with higher capacity |
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Hi Vincent,
On 08/26/2014 04:36 PM, Vincent Guittot wrote: > If the CPU is used for handling lot of IRQs, trig a load balance to check if > it's worth moving its tasks on another CPU that has more capacity. > > As a sidenote, this will note generate more spurious ilb because we already > trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that > has a task, we will trig the ilb once for migrating the task. > > The nohz_kick_needed function has been cleaned up a bit while adding the new > test > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/fair.c | 69 +++++++++++++++++++++++++++++++++++++---------------- > 1 file changed, 49 insertions(+), 20 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 18db43e..60ae1ce 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6049,6 +6049,14 @@ static bool update_sd_pick_busiest(struct lb_env *env, > return true; > } > > + /* > + * The group capacity is reduced probably because of activity from other > + * sched class or interrupts which use part of the available capacity > + */ > + if ((sg->sgc->capacity_orig * 100) > (sgs->group_capacity * > + env->sd->imbalance_pct))
Wouldn't the check on avg_load let us know if we are packing more tasks in this group than its capacity ? Isn't that the metric we are more interested in?
> + return true; > + > return false; > } > > @@ -6534,13 +6542,23 @@ static int need_active_balance(struct lb_env *env) > struct sched_domain *sd = env->sd; > > if (env->idle == CPU_NEWLY_IDLE) { > + int src_cpu = env->src_cpu; > > /* > * ASYM_PACKING needs to force migrate tasks from busy but > * higher numbered CPUs in order to pack all tasks in the > * lowest numbered CPUs. > */ > - if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu) > + if ((sd->flags & SD_ASYM_PACKING) && src_cpu > env->dst_cpu) > + return 1; > + > + /* > + * If the CPUs share their cache and the src_cpu's capacity is > + * reduced because of other sched_class or IRQs, we trig an > + * active balance to move the task > + */ > + if ((capacity_orig_of(src_cpu) * 100) > (capacity_of(src_cpu) * > + sd->imbalance_pct)) > return 1; > } > > @@ -6643,6 +6661,8 @@ static int load_balance(int this_cpu, struct rq *this_rq, > > schedstat_add(sd, lb_imbalance[idle], env.imbalance); > > + env.src_cpu = busiest->cpu; > + > ld_moved = 0; > if (busiest->nr_running > 1) { > /* > @@ -6652,7 +6672,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, > * correctly treated as an imbalance. > */ > env.flags |= LBF_ALL_PINNED; > - env.src_cpu = busiest->cpu; > env.src_rq = busiest; > env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running); > > @@ -7359,10 +7378,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) > > /* > * Current heuristic for kicking the idle load balancer in the presence > - * of an idle cpu is the system. > + * of an idle cpu in 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 capacity. > + * - This rq has at least one CFS task and the capacity of the CPU is > + * significantly reduced because of RT tasks or IRQs. > + * - At parent of LLC scheduler domain level, this cpu's scheduler group has > + * multiple busy cpu. > * - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler > * domain span are idle. > */ > @@ -7372,9 +7393,10 @@ static inline int nohz_kick_needed(struct rq *rq) > struct sched_domain *sd; > struct sched_group_capacity *sgc; > int nr_busy, cpu = rq->cpu; > + bool kick = false; > > if (unlikely(rq->idle_balance)) > - return 0; > + return false; > > /* > * We may be recently in ticked or tickless idle mode. At the first > @@ -7388,38 +7410,45 @@ static inline int nohz_kick_needed(struct rq *rq) > * balancing. > */ > if (likely(!atomic_read(&nohz.nr_cpus))) > - return 0; > + return false; > > if (time_before(now, nohz.next_balance)) > - return 0; > + return false; > > if (rq->nr_running >= 2)
Will this check ^^ not catch those cases which this patch is targeting?
Regards Preeti U Murthy
> - goto need_kick; > + return true; > > rcu_read_lock(); > sd = rcu_dereference(per_cpu(sd_busy, cpu)); > - > if (sd) { > sgc = sd->groups->sgc; > nr_busy = atomic_read(&sgc->nr_busy_cpus); > > - if (nr_busy > 1) > - goto need_kick_unlock; > + if (nr_busy > 1) { > + kick = true; > + goto unlock; > + } > + > } > > - sd = rcu_dereference(per_cpu(sd_asym, cpu)); > + sd = rcu_dereference(rq->sd); > + if (sd) { > + if ((rq->cfs.h_nr_running >= 1) && > + ((rq->cpu_capacity * sd->imbalance_pct) < > + (rq->cpu_capacity_orig * 100))) { > + kick = true; > + goto unlock; > + } > + } > > + sd = rcu_dereference(per_cpu(sd_asym, cpu)); > if (sd && (cpumask_first_and(nohz.idle_cpus_mask, > sched_domain_span(sd)) < cpu)) > - goto need_kick_unlock; > + kick = true; > > +unlock: > rcu_read_unlock(); > - return 0; > - > -need_kick_unlock: > - rcu_read_unlock(); > -need_kick: > - return 1; > + return kick; > } > #else > static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { } >
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