[PATCH] Per Sched domain over utilization - eas-dev

25 Jan 2017

The current implementation of overutilization, aborts energy aware
scheduling if any cpu in the system is over-utilized. This patch introduces
over utilization flag per sched domain level instead of a single flag
system wide.  Load balancing is done at the sched domain where any
of the cpu is over utilized. If energy aware scheduling is
enabled and no cpu in a sched domain is overuttilized,
load balancing is skipped for that sched domain and energy aware
scheduling continues at that level.
The implementation takes advantage of the shared sched_domain structure
that is common across all the sched domains at a level. The new flag
introduced is placed in this structure so that all the sched domains the
same level share the flag. In case of an overutilized cpu, the flag gets
set at level1 sched_domain. The flag at the parent sched_domain level gets
set in either of the two following scenarios.
 1. There is a misfit task in one of the cpu's in this sched_domain.
 2. The total utilization of the domain is greater than the domain capacity
The flag is cleared if no cpu in a sched domain is overutilized.
Signed-off-by: Thara Gopinath thara.gopinath@linaro.org
---
 include/linux/sched.h |   1 +
 kernel/sched/core.c   |   7 ++-
 kernel/sched/fair.c   | 120 +++++++++++++++++++++++++++++++++++++++-----------
 3 files changed, 99 insertions(+), 29 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1c5122e..971842a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1112,6 +1112,7 @@ struct sched_domain_shared {
    atomic_t	ref;
    atomic_t	nr_busy_cpus;
    int		has_idle_cores;
+	bool		overutilized;
 };
struct sched_domain {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 31a466f..e0a8758 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6659,11 +6659,10 @@ sd_init(struct sched_domain_topology_level *tl,
     * For all levels sharing cache; connect a sched_domain_shared
     * instance.
     */
-	if (sd->flags & SD_SHARE_PKG_RESOURCES) {
-		sd->shared = *per_cpu_ptr(sdd->sds, sd_id);
-		atomic_inc(&sd->shared->ref);
+	sd->shared = *per_cpu_ptr(sdd->sds, sd_id);
+	atomic_inc(&sd->shared->ref);
+	if (sd->flags & SD_SHARE_PKG_RESOURCES)
    	atomic_set(&sd->shared->nr_busy_cpus, sd_weight);
-	}
sd->private = sdd;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 489f6d3..485f597 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4735,6 +4735,30 @@ static inline void hrtick_update(struct rq *rq)
static bool cpu_overutilized(int cpu);
+static bool
+is_sd_overutilized(struct sched_domain *sd)
+{
+	if (sd)
+		return sd->shared->overutilized;
+	else
+		return false;
+}
+
+static void
+set_sd_overutilized(struct sched_domain *sd)
+{
+	if (sd)
+		sd->shared->overutilized = true;
+}
+
+static void
+clear_sd_overutilized(struct sched_domain *sd)
+{
+	if (sd)
+		sd->shared->overutilized = false;
+}
+
+
 /*
  * The enqueue_task method is called before nr_running is
  * increased. Here we update the fair scheduling stats and
@@ -4744,6 +4768,7 @@ static void
 enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
    struct cfs_rq *cfs_rq;
+	struct sched_domain *sd;
    struct sched_entity *se = &p->se;
    int task_new = !(flags & ENQUEUE_WAKEUP);
@@ -4787,9 +4812,12 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
if (!se) {
    	add_nr_running(rq, 1);
-		if (!task_new && !rq->rd->overutilized &&
-		    cpu_overutilized(rq->cpu))
-			rq->rd->overutilized = true;
+		rcu_read_lock();
+		sd = rcu_dereference(rq->sd);
+		if (!task_new && !is_sd_overutilized(sd) &&
+			cpu_overutilized(rq->cpu))
+				set_sd_overutilized(sd);
+		rcu_read_unlock();
    }
    hrtick_update(rq);
 }
@@ -6173,8 +6201,7 @@ static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu)
    unsigned long max_spare = 0;
    struct sched_domain *sd;
-	rcu_read_lock();
-
+	/* The rcu lock is/should be held in the caller function */
    sd = rcu_dereference(per_cpu(sd_ea, prev_cpu));
if (!sd)
@@ -6212,8 +6239,6 @@ static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu)
    }
unlock:
-	rcu_read_unlock();
-
    if (energy_cpu == prev_cpu && !cpu_overutilized(prev_cpu))
    	return prev_cpu;
@@ -6247,10 +6272,16 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
    		      && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
    }
-	if (energy_aware() && !(cpu_rq(prev_cpu)->rd->overutilized))
-		return select_energy_cpu_brute(p, prev_cpu);
-
    rcu_read_lock();
+	sd = rcu_dereference(cpu_rq(prev_cpu)->sd);
+	if (energy_aware() &&
+			!is_sd_overutilized(sd)) {
+		new_cpu = select_energy_cpu_brute(p, prev_cpu);
+		goto unlock;
+	}
+
+	sd = NULL;
+
    for_each_domain(cpu, tmp) {
    	if (!(tmp->flags & SD_LOAD_BALANCE))
    		break;
@@ -6315,6 +6346,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
    	}
    	/* while loop will break here if sd == NULL */
    }
+
+unlock:
    rcu_read_unlock();
return new_cpu;
@@ -7366,6 +7399,7 @@ struct sd_lb_stats {
    struct sched_group *local;	/* Local group in this sd */
    unsigned long total_load;	/* Total load of all groups in sd */
    unsigned long total_capacity;	/* Total capacity of all groups in sd */
+	unsigned long total_util;	/* Total util of all groups in sd */
    unsigned long avg_load;	/* Average load across all groups in sd */
struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */
@@ -7385,6 +7419,7 @@ static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
    	.local = NULL,
    	.total_load = 0UL,
    	.total_capacity = 0UL,
+		.total_util = 0UL,
    	.busiest_stat = {
    		.avg_load = 0UL,
    		.sum_nr_running = 0,
@@ -7664,7 +7699,7 @@ group_type group_classify(struct sched_group *group,
 static inline void update_sg_lb_stats(struct lb_env *env,
    		struct sched_group *group, int load_idx,
    		int local_group, struct sg_lb_stats *sgs,
-			bool *overload, bool *overutilized)
+			bool *overload, bool *overutilized, bool *misfit_task)
 {
    unsigned long load;
    int i, nr_running;
@@ -7699,8 +7734,16 @@ static inline void update_sg_lb_stats(struct lb_env *env,
    	if (!nr_running && idle_cpu(i))
    		sgs->idle_cpus++;
-		if (cpu_overutilized(i))
+		if (cpu_overutilized(i)) {
    		*overutilized = true;
+		/*
+		 * If the cpu is overutilized and if there is only one
+		 * current task in cfs runqueue, it is potentially a misfit
+		 * task.
+		 */
+			if (rq->cfs.h_nr_running == 1)
+				*misfit_task = true;
+		}
    }
/* Adjust by relative CPU capacity of the group */
@@ -7829,7 +7872,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
    struct sched_group *sg = env->sd->groups;
    struct sg_lb_stats tmp_sgs;
    int load_idx, prefer_sibling = 0;
-	bool overload = false, overutilized = false;
+	bool overload = false, overutilized = false, misfit_task = false;
if (child && child->flags & SD_PREFER_SIBLING)
    	prefer_sibling = 1;
@@ -7851,7 +7894,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
    	}
update_sg_lb_stats(env, sg, load_idx, local_group, sgs,
-						&overload, &overutilized);
+						&overload, &overutilized,
+						&misfit_task);
if (local_group)
    		goto next_group;
@@ -7882,6 +7926,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
    	/* Now, start updating sd_lb_stats */
    	sds->total_load += sgs->group_load;
    	sds->total_capacity += sgs->group_capacity;
+		sds->total_util += sgs->group_util;
sg = sg->next;
    } while (sg != env->sd->groups);
@@ -7895,14 +7940,27 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
    	/* update overload indicator if we are at root domain */
    	if (env->dst_rq->rd->overload != overload)
    		env->dst_rq->rd->overload = overload;
-
-		/* Update over-utilization (tipping point, U >= 0) indicator */
-		if (env->dst_rq->rd->overutilized != overutilized)
-			env->dst_rq->rd->overutilized = overutilized;
-	} else {
-		if (!env->dst_rq->rd->overutilized && overutilized)
-			env->dst_rq->rd->overutilized = true;
    }
+
+	if (overutilized)
+		set_sd_overutilized(env->sd);
+	else
+		clear_sd_overutilized(env->sd);
+
+	/*
+	 * If there is a misfit task in one cpu in this sched_domain
+	 * it is likely that the imbalance cannot be sorted out among
+	 * the cpu's in this sched_domain. In this case set the
+	 * overutilized flag at the parent sched_domain.
+	 */
+	if (misfit_task)
+		set_sd_overutilized(env->sd->parent);
+
+	/* If the domain util is greater that domain capacity, load balancing
+	 * needs to be done at the next sched domain level as well
+	 */
+	if (sds->total_capacity * 1024 < sds->total_util * capacity_margin)
+		set_sd_overutilized(env->sd->parent);
 }
/**
@@ -8122,8 +8180,10 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
     */
    update_sd_lb_stats(env, &sds);
-	if (energy_aware() && !env->dst_rq->rd->overutilized)
-		goto out_balanced;
+	if (energy_aware()) {
+		if (!is_sd_overutilized(env->sd))
+			goto out_balanced;
+	}
local = &sds.local_stat;
    busiest = &sds.busiest_stat;
@@ -8981,6 +9041,11 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
rcu_read_lock();
    for_each_domain(cpu, sd) {
+		if (energy_aware()) {
+			if (!is_sd_overutilized(sd))
+				continue;
+		}
+
    	/*
    	 * Decay the newidle max times here because this is a regular
    	 * visit to all the domains. Decay ~1% per second.
@@ -9280,6 +9345,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 {
    struct cfs_rq *cfs_rq;
    struct sched_entity *se = &curr->se;
+	struct sched_domain *sd;
for_each_sched_entity(se) {
    	cfs_rq = cfs_rq_of(se);
@@ -9289,8 +9355,12 @@ 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);
-	if (!rq->rd->overutilized && cpu_overutilized(task_cpu(curr)))
-		rq->rd->overutilized = true;
+	rcu_read_lock();
+	sd = rcu_dereference(rq->sd);
+	if (!is_sd_overutilized(sd) &&
+		cpu_overutilized(task_cpu(curr)))
+			set_sd_overutilized(sd);
+	rcu_read_unlock();
 }
/*
--
2.1.4

    