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)) + 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) - 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) { }