Commit-ID: 3b1baa6496e6b7ad016342a9d256bdfb072ce902
Gitweb: https://git.kernel.org/tip/3b1baa6496e6b7ad016342a9d256bdfb072ce902
Author: Morten Rasmussen <morten.rasmus...@arm.com>
AuthorDate: Wed, 4 Jul 2018 11:17:40 +0100
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Mon, 10 Sep 2018 11:05:49 +0200
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: Morten Rasmussen <morten.rasmus...@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: dietmar.eggem...@arm.com
Cc: gaku.inami...@renesas.com
Cc: valentin.schnei...@arm.com
Cc: vincent.guit...@linaro.org
Link:
http://lkml.kernel.org/r/1530699470-29808-3-git-send-email-morten.rasmus...@arm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
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 3e5071aeb117..6e04bea5b11a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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);
}
/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0f36adc31ba5..7dbf67d147a2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -842,6 +842,8 @@ struct rq {
unsigned char idle_balance;
+ unsigned long misfit_task_load;
+
/* For active balancing */
int active_balance;
int push_cpu;
