From: Uladzislau 2 Rezki <[email protected]> A load balancer calculates imbalance factor for particular shed domain and tries to steal up the prescribed amount of weighted load. However, a small imbalance factor would sometimes prevent us from stealing any tasks at all. When a CPU is newly idle, it should steal first task which passes a migration criteria.
Signed-off-by: Uladzislau 2 Rezki <[email protected]> --- kernel/sched/fair.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 232ef3c..29e0d7f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6802,6 +6802,14 @@ static int detach_tasks(struct lb_env *env) if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1) break; + /* + * Another CPU can place tasks, since we do not hold dst_rq lock + * while doing balancing. If newly idle CPU already got something, + * give up to reduce latency. + */ + if (env->idle == CPU_NEWLY_IDLE && env->dst_rq->nr_running > 0) + break; + p = list_first_entry(tasks, struct task_struct, se.group_node); env->loop++; @@ -6824,8 +6832,9 @@ static int detach_tasks(struct lb_env *env) if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed) goto next; - if ((load / 2) > env->imbalance) - goto next; + if (env->idle != CPU_NEWLY_IDLE) + if ((load / 2) > env->imbalance) + goto next; detach_task(p, env); list_add(&p->se.group_node, &env->tasks); -- 2.1.4
