From edb839a29c08b4313c4cbecfae666677ce1815b9 Mon Sep 17 00:00:00 2001 From: Morten Rasmussen Date: Thu, 25 Feb 2016 12:47:54 +0000 Subject: [PATCH] sched: Add group_misfit_task load-balance type To maximize throughput in systems with reduced capacity cpus (e.g. high RT/IRQ load and/or 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 that are scheduled on a reduced capacity cpu need to be identified and migrated to a higher capacity cpu if possible. 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 tasks that are not suitable for its per-cpu capacity. group_misfit_task is only considered if the system is not overloaded in any other way (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. Signed-off-by: Morten Rasmussen --- kernel/sched/fair.c | 29 ++++++++++++++++++++++------- kernel/sched/sched.h | 1 + 2 files changed, 23 insertions(+), 7 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 618e94ef803b..6c791547225c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5760,6 +5760,8 @@ again: if (hrtick_enabled(rq)) hrtick_start_fair(rq, p); + rq->misfit_task = !task_fits_max(p, rq->cpu); + return p; simple: cfs_rq = &rq->cfs; @@ -5781,9 +5783,12 @@ simple: if (hrtick_enabled(rq)) hrtick_start_fair(rq, p); + rq->misfit_task = !task_fits_max(p, rq->cpu); + return p; idle: + rq->misfit_task = 0; /* * This is OK, because current is on_cpu, which avoids it being picked * for load-balance and preemption/IRQs are still disabled avoiding @@ -5996,6 +6001,13 @@ 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 @@ -6467,12 +6479,6 @@ 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 */ @@ -6488,6 +6494,7 @@ struct sg_lb_stats { unsigned int group_weight; enum group_type group_type; int group_no_capacity; + int group_misfit_task; /* A cpu has a task too big for its capacity */ #ifdef CONFIG_NUMA_BALANCING unsigned int nr_numa_running; unsigned int nr_preferred_running; @@ -6804,6 +6811,9 @@ group_type group_classify(struct sched_group *group, if (sg_imbalanced(group)) return group_imbalanced; + if (sgs->group_misfit_task) + return group_misfit_task; + return group_other; } @@ -6851,8 +6861,11 @@ static inline void update_sg_lb_stats(struct lb_env *env, if (idle_cpu(i)) sgs->idle_cpus++; - if (cpu_overutilized(i)) + if (cpu_overutilized(i)) { *overutilized = true; + if (!sgs->group_misfit_task && rq->misfit_task) + sgs->group_misfit_task = capacity_of(i); + } } /* Adjust by relative CPU capacity of the group */ @@ -8433,6 +8446,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) if (!rq->rd->overutilized && cpu_overutilized(task_cpu(curr))) rq->rd->overutilized = true; + + rq->misfit_task = !task_fits_max(curr, rq->cpu); } /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 33583123792e..d4f9ddfbff73 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -584,6 +584,7 @@ struct rq { #define CPU_LOAD_IDX_MAX 5 unsigned long cpu_load[CPU_LOAD_IDX_MAX]; unsigned long last_load_update_tick; + unsigned int misfit_task; #ifdef CONFIG_NO_HZ_COMMON u64 nohz_stamp; unsigned long nohz_flags; -- 2.34.1