Commit 3b1baa64 authored by Morten Rasmussen's avatar Morten Rasmussen Committed by Ingo Molnar

sched/fair: Add 'group_misfit_task' load-balance type

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.
Signed-off-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: gaku.inami.xh@renesas.com
Cc: valentin.schneider@arm.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1530699470-29808-3-git-send-email-morten.rasmussen@arm.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent df054e84
......@@ -693,6 +693,7 @@ 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)
......@@ -1446,7 +1447,6 @@ 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 {
......@@ -3647,6 +3647,29 @@ 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 */
#define UPDATE_TG 0x0
......@@ -3676,6 +3699,7 @@ 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 */
......@@ -6201,7 +6225,7 @@ 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);
}
/*
......@@ -6618,9 +6642,12 @@ 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);
/*
......@@ -6826,6 +6853,13 @@ 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
......@@ -7399,12 +7433,6 @@ 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
*/
......@@ -7420,6 +7448,7 @@ 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;
......@@ -7712,6 +7741,9 @@ 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;
}
......@@ -7786,6 +7818,10 @@ 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 */
......@@ -9567,6 +9603,8 @@ 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);
}
/*
......
......@@ -842,6 +842,8 @@ struct rq {
unsigned char idle_balance;
unsigned long misfit_task_load;
/* For active balancing */
int active_balance;
int push_cpu;
......
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