To maximize throughput in systems with asymmetric cpu capacities (e.g. ARM big.LITTLE) load-balancing has to consider task and cpu utilization as well as per-cpu compute capacity when load-balancing in addition to the current average load based load-balancing policy. Tasks with high utilization that are scheduled on a lower capacity cpu need to be identified and migrated to a higher capacity cpu if possible to maximize throughput.
To implement this additional policy an additional group_type (load-balance scenario) is added: group_misfit_task. This represents scenarios where a sched_group has one or more tasks that are not suitable for its per-cpu capacity. group_misfit_task is only considered if the system is not overloaded or imbalanced (group_imbalanced or group_overloaded). Identifying misfit tasks requires the rq lock to be held. To avoid taking remote rq locks to examine source sched_groups for misfit tasks, each cpu is responsible for tracking misfit tasks themselves and update the rq->misfit_task flag. This means checking task utilization when tasks are scheduled and on sched_tick. cc: Ingo Molnar <[email protected]> cc: Peter Zijlstra <[email protected]> Signed-off-by: Morten Rasmussen <[email protected]> --- kernel/sched/fair.c | 54 ++++++++++++++++++++++++++++++++++++++++++++-------- kernel/sched/sched.h | 2 ++ 2 files changed, 48 insertions(+), 8 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6116d1b7e441..ed7eb2ac068f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -697,6 +697,7 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se) static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu); static unsigned long task_h_load(struct task_struct *p); +static unsigned long capacity_of(int cpu); /* Give new sched_entity start runnable values to heavy its load in infant time */ void init_entity_runnable_average(struct sched_entity *se) @@ -1448,7 +1449,6 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page, static unsigned long weighted_cpuload(struct rq *rq); static unsigned long source_load(int cpu, int type); static unsigned long target_load(int cpu, int type); -static unsigned long capacity_of(int cpu); /* Cached statistics for all CPUs within a node */ struct numa_stats { @@ -4043,6 +4043,29 @@ util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep) WRITE_ONCE(p->se.avg.util_est, ue); } +static inline int task_fits_capacity(struct task_struct *p, long capacity) +{ + return capacity * 1024 > task_util_est(p) * capacity_margin; +} + +static inline void update_misfit_status(struct task_struct *p, struct rq *rq) +{ + if (!static_branch_unlikely(&sched_asym_cpucapacity)) + return; + + if (!p) { + rq->misfit_task_load = 0; + return; + } + + if (task_fits_capacity(p, capacity_of(cpu_of(rq)))) { + rq->misfit_task_load = 0; + return; + } + + rq->misfit_task_load = task_h_load(p); +} + #else /* CONFIG_SMP */ static inline int @@ -4078,6 +4101,7 @@ util_est_enqueue(struct cfs_rq *cfs_rq, struct task_struct *p) {} static inline void util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep) {} +static inline void update_misfit_status(struct task_struct *p, struct rq *rq) {} #endif /* CONFIG_SMP */ @@ -6598,7 +6622,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) /* Bring task utilization in sync with prev_cpu */ sync_entity_load_avg(&p->se); - return min_cap * 1024 < task_util(p) * capacity_margin; + return !task_fits_capacity(p, min_cap); } /* @@ -7015,9 +7039,12 @@ done: __maybe_unused; if (hrtick_enabled(rq)) hrtick_start_fair(rq, p); + update_misfit_status(p, rq); + return p; idle: + update_misfit_status(NULL, rq); new_tasks = idle_balance(rq, rf); /* @@ -7223,6 +7250,13 @@ static unsigned long __read_mostly max_load_balance_interval = HZ/10; enum fbq_type { regular, remote, all }; +enum group_type { + group_other = 0, + group_misfit_task, + group_imbalanced, + group_overloaded, +}; + #define LBF_ALL_PINNED 0x01 #define LBF_NEED_BREAK 0x02 #define LBF_DST_PINNED 0x04 @@ -7764,12 +7798,6 @@ static unsigned long task_h_load(struct task_struct *p) /********** Helpers for find_busiest_group ************************/ -enum group_type { - group_other = 0, - group_imbalanced, - group_overloaded, -}; - /* * sg_lb_stats - stats of a sched_group required for load_balancing */ @@ -7785,6 +7813,7 @@ struct sg_lb_stats { unsigned int group_weight; enum group_type group_type; int group_no_capacity; + unsigned long group_misfit_task_load; /* A cpu has a task too big for its capacity */ #ifdef CONFIG_NUMA_BALANCING unsigned int nr_numa_running; unsigned int nr_preferred_running; @@ -8084,6 +8113,9 @@ group_type group_classify(struct sched_group *group, if (sg_imbalanced(group)) return group_imbalanced; + if (sgs->group_misfit_task_load) + return group_misfit_task; + return group_other; } @@ -8158,6 +8190,10 @@ static inline void update_sg_lb_stats(struct lb_env *env, */ if (!nr_running && idle_cpu(i)) sgs->idle_cpus++; + + if (env->sd->flags & SD_ASYM_CPUCAPACITY && + sgs->group_misfit_task_load < rq->misfit_task_load) + sgs->group_misfit_task_load = rq->misfit_task_load; } /* Adjust by relative CPU capacity of the group */ @@ -9939,6 +9975,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) if (static_branch_unlikely(&sched_numa_balancing)) task_tick_numa(rq, curr); + + update_misfit_status(curr, rq); } /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 0fbfbcf5c551..273d07dedc90 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -815,6 +815,8 @@ struct rq { unsigned char idle_balance; + unsigned long misfit_task_load; + /* For active balancing */ int active_balance; int push_cpu; -- 2.7.4
