From a7455f8123479ddcad3ff7b366ce143cb78a9ae3 Mon Sep 17 00:00:00 2001 From: Chris Redpath Date: Tue, 5 Jun 2018 11:47:57 +0100 Subject: [PATCH] ANDROID: sched/fair: Don't balance misfits if it would overload local group When load balancing in a system with misfit tasks present, if we always pull a misfit task to the local group this can lead to pulling a running task from a smaller capacity CPUs to a bigger CPU which is busy. In this situation, the pulled task is likely not to get a chance to run before an idle balance on another small CPU pulls it back. This penalises the pulled task as it is stopped for a short amount of time and then likely relocated to a different CPU (since the original CPU just did a NEWLY_IDLE balance and reset the periodic interval). If we only do this unconditionally for NEWLY_IDLE balance, we can be sure that any tasks and load which are present on the local group are related to short-running tasks which we are happy to displace for a longer running task in a system with misfit tasks present. However, other balance types should only pull a task if we think that the local group is underutilized - checking the number of tasks gives us a conservative estimate here since if they were short tasks we would have been doing NEWLY_IDLE balances instead. Change-Id: I710add1ab1139482620b6addc8370ad194791beb Signed-off-by: Chris Redpath Signed-off-by: Quentin Perret --- kernel/sched/fair.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1962e68fcf60..af23c63eca32 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8509,8 +8509,18 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s (sds->avg_load - local->avg_load) * local->group_capacity ) / SCHED_CAPACITY_SCALE; - /* Boost imbalance to allow misfit task to be balanced. */ - if (busiest->group_type == group_misfit_task) { + /* Boost imbalance to allow misfit task to be balanced. + * Always do this if we are doing a NEWLY_IDLE balance + * on the assumption that any tasks we have must not be + * long-running (and hence we cannot rely upon load). + * However if we are not idle, we should assume the tasks + * we have are longer running and not override load-based + * calculations above unless we are sure that the local + * group is underutilized. + */ + if (busiest->group_type == group_misfit_task && + (env->idle == CPU_NEWLY_IDLE || + local->sum_nr_running < local->group_weight)) { env->imbalance = max_t(long, env->imbalance, busiest->group_misfit_task_load); }