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
env.src_cpu and env.src_rq must be set unconditionnaly because they are used in need_active_balance which is called even if busiest->nr_running equals 1
Signed-off-by: Vincent Guittot vincent.guittot@linaro.org --- kernel/sched/fair.c | 70 ++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 50 insertions(+), 20 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 622f8b0..7422044 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5885,6 +5885,18 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group) }
/* + * Check whether the capacity of the rq has been noticeably reduced by side + * activity. The imbalance_pct is used for the threshold. + * Return true is the capacity is reduced + */ +static inline int +check_cpu_capacity(struct rq *rq, struct sched_domain *sd) +{ + return ((rq->cpu_capacity * sd->imbalance_pct) < + (rq->cpu_capacity_orig * 100)); +} + +/* * Group imbalance indicates (and tries to solve) the problem where balancing * groups is inadequate due to tsk_cpus_allowed() constraints. * @@ -6555,6 +6567,14 @@ static int need_active_balance(struct lb_env *env) */ if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu) return 1; + + /* + * The src_cpu's capacity is reduced because of other + * sched_class or IRQs, we trig an active balance to move the + * task + */ + if (check_cpu_capacity(env->src_rq, sd)) + return 1; }
return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2); @@ -6656,6 +6676,9 @@ static int load_balance(int this_cpu, struct rq *this_rq,
schedstat_add(sd, lb_imbalance[idle], env.imbalance);
+ env.src_cpu = busiest->cpu; + env.src_rq = busiest; + ld_moved = 0; if (busiest->nr_running > 1) { /* @@ -6665,8 +6688,6 @@ 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);
more_balance: @@ -7372,10 +7393,12 @@ 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. */ @@ -7385,9 +7408,10 @@ 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 @@ -7401,38 +7425,44 @@ 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) && + check_cpu_capacity(rq, sd)) { + 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; - - rcu_read_unlock(); - return 0; + kick = true;
-need_kick_unlock: +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) { }