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sched: Add group_misfit_task load-balance type

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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 <morten.rasmussen@arm.com>
This commit is contained in:
Morten Rasmussen
2016-02-25 12:47:54 +00:00
committed by Leo Yan
parent 563ddb604e
commit f2a8923298
2 changed files with 23 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
kernel/sched/fair.c
View File

@@ -5739,6 +5739,8 @@ 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;
@@ -5760,9 +5762,12 @@ 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
@@ -5975,6 +5980,13 @@ 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
@@ -6446,12 +6458,6 @@ 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
*/
@@ -6467,6 +6473,7 @@ 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;
@@ -6783,6 +6790,9 @@ 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;
}
@@ -6830,8 +6840,11 @@ 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 */
@@ -8412,6 +8425,8 @@ 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);
}
/*

1
kernel/sched/sched.h
View File

@@ -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;