1 files changed, 109 insertions, 107 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 373ff5f55884..48b6f0ca13ac 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1064,6 +1064,23 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
  * Scheduling class queueing methods:
  */
 
+static inline bool is_core_idle(int cpu)
+{
+#ifdef CONFIG_SCHED_SMT
+	int sibling;
+
+	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
+		if (cpu == sibling)
+			continue;
+
+		if (!idle_cpu(sibling))
+			return false;
+	}
+#endif
+
+	return true;
+}
+
 #ifdef CONFIG_NUMA
 #define NUMA_IMBALANCE_MIN 2
 
@@ -1700,23 +1717,6 @@ struct numa_stats {
 	int idle_cpu;
 };
 
-static inline bool is_core_idle(int cpu)
-{
-#ifdef CONFIG_SCHED_SMT
-	int sibling;
-
-	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
-		if (cpu == sibling)
-			continue;
-
-		if (!idle_cpu(sibling))
-			return false;
-	}
-#endif
-
-	return true;
-}
-
 struct task_numa_env {
 	struct task_struct *p;
 
@@ -9331,96 +9331,61 @@ group_type group_classify(unsigned int imbalance_pct,
 }
 
 /**
- * asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks
- * @dst_cpu:	Destination CPU of the load balancing
+ * sched_use_asym_prio - Check whether asym_packing priority must be used
+ * @sd:		The scheduling domain of the load balancing
+ * @cpu:	A CPU
+ *
+ * Always use CPU priority when balancing load between SMT siblings. When
+ * balancing load between cores, it is not sufficient that @cpu is idle. Only
+ * use CPU priority if the whole core is idle.
+ *
+ * Returns: True if the priority of @cpu must be followed. False otherwise.
+ */
+static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
+{
+	if (!sched_smt_active())
+		return true;
+
+	return sd->flags & SD_SHARE_CPUCAPACITY || is_core_idle(cpu);
+}
+
+/**
+ * sched_asym - Check if the destination CPU can do asym_packing load balance
+ * @env:	The load balancing environment
  * @sds:	Load-balancing data with statistics of the local group
  * @sgs:	Load-balancing statistics of the candidate busiest group
- * @sg:		The candidate busiest group
- *
- * Check the state of the SMT siblings of both @sds::local and @sg and decide
- * if @dst_cpu can pull tasks.
+ * @group:	The candidate busiest group
  *
- * If @dst_cpu does not have SMT siblings, it can pull tasks if two or more of
- * the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks
- * only if @dst_cpu has higher priority.
+ * @env::dst_cpu can do asym_packing if it has higher priority than the
+ * preferred CPU of @group.
  *
- * If both @dst_cpu and @sg have SMT siblings, and @sg has exactly one more
- * busy CPU than @sds::local, let @dst_cpu pull tasks if it has higher priority.
- * Bigger imbalances in the number of busy CPUs will be dealt with in
- * update_sd_pick_busiest().
+ * SMT is a special case. If we are balancing load between cores, @env::dst_cpu
+ * can do asym_packing balance only if all its SMT siblings are idle. Also, it
+ * can only do it if @group is an SMT group and has exactly on busy CPU. Larger
+ * imbalances in the number of CPUS are dealt with in find_busiest_group().
  *
- * If @sg does not have SMT siblings, only pull tasks if all of the SMT siblings
- * of @dst_cpu are idle and @sg has lower priority.
+ * If we are balancing load within an SMT core, or at DIE domain level, always
+ * proceed.
  *
- * Return: true if @dst_cpu can pull tasks, false otherwise.
+ * Return: true if @env::dst_cpu can do with asym_packing load balance. False
+ * otherwise.
  */
-static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
-				    struct sg_lb_stats *sgs,
-				    struct sched_group *sg)
+static inline bool
+sched_asym(struct lb_env *env, struct sd_lb_stats *sds,  struct sg_lb_stats *sgs,
+	   struct sched_group *group)
 {
-#ifdef CONFIG_SCHED_SMT
-	bool local_is_smt, sg_is_smt;
-	int sg_busy_cpus;
-
-	local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY;
-	sg_is_smt = sg->flags & SD_SHARE_CPUCAPACITY;
-
-	sg_busy_cpus = sgs->group_weight - sgs->idle_cpus;
-
-	if (!local_is_smt) {
-		/*
-		 * If we are here, @dst_cpu is idle and does not have SMT
-		 * siblings. Pull tasks if candidate group has two or more
-		 * busy CPUs.
-		 */
-		if (sg_busy_cpus >= 2) /* implies sg_is_smt */
-			return true;
-
-		/*
-		 * @dst_cpu does not have SMT siblings. @sg may have SMT
-		 * siblings and only one is busy. In such case, @dst_cpu
-		 * can help if it has higher priority and is idle (i.e.,
-		 * it has no running tasks).
-		 */
-		return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
-	}
-
-	/* @dst_cpu has SMT siblings. */
-
-	if (sg_is_smt) {
-		int local_busy_cpus = sds->local->group_weight -
-				      sds->local_stat.idle_cpus;
-		int busy_cpus_delta = sg_busy_cpus - local_busy_cpus;
-
-		if (busy_cpus_delta == 1)
-			return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
-
+	/* Ensure that the whole local core is idle, if applicable. */
+	if (!sched_use_asym_prio(env->sd, env->dst_cpu))
 		return false;
-	}
 
 	/*
-	 * @sg does not have SMT siblings. Ensure that @sds::local does not end
-	 * up with more than one busy SMT sibling and only pull tasks if there
-	 * are not busy CPUs (i.e., no CPU has running tasks).
+	 * CPU priorities does not make sense for SMT cores with more than one
+	 * busy sibling.
 	 */
-	if (!sds->local_stat.sum_nr_running)
-		return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
-
-	return false;
-#else
-	/* Always return false so that callers deal with non-SMT cases. */
-	return false;
-#endif
-}
-
-static inline bool
-sched_asym(struct lb_env *env, struct sd_lb_stats *sds,  struct sg_lb_stats *sgs,
-	   struct sched_group *group)
-{
-	/* Only do SMT checks if either local or candidate have SMT siblings */
-	if ((sds->local->flags & SD_SHARE_CPUCAPACITY) ||
-	    (group->flags & SD_SHARE_CPUCAPACITY))
-		return asym_smt_can_pull_tasks(env->dst_cpu, sds, sgs, group);
+	if (group->flags & SD_SHARE_CPUCAPACITY) {
+		if (sgs->group_weight - sgs->idle_cpus != 1)
+			return false;
+	}
 
 	return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
 }
@@ -9610,10 +9575,22 @@ static bool update_sd_pick_busiest(struct lb_env *env,
 		 * contention when accessing shared HW resources.
 		 *
 		 * XXX for now avg_load is not computed and always 0 so we
-		 * select the 1st one.
+		 * select the 1st one, except if @sg is composed of SMT
+		 * siblings.
 		 */
-		if (sgs->avg_load <= busiest->avg_load)
+
+		if (sgs->avg_load < busiest->avg_load)
 			return false;
+
+		if (sgs->avg_load == busiest->avg_load) {
+			/*
+			 * SMT sched groups need more help than non-SMT groups.
+			 * If @sg happens to also be SMT, either choice is good.
+			 */
+			if (sds->busiest->flags & SD_SHARE_CPUCAPACITY)
+				return false;
+		}
+
 		break;
 
 	case group_has_spare:
@@ -10088,7 +10065,6 @@ static void update_idle_cpu_scan(struct lb_env *env,
 
 static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
 {
-	struct sched_domain *child = env->sd->child;
 	struct sched_group *sg = env->sd->groups;
 	struct sg_lb_stats *local = &sds->local_stat;
 	struct sg_lb_stats tmp_sgs;
@@ -10129,8 +10105,13 @@ next_group:
 		sg = sg->next;
 	} while (sg != env->sd->groups);
 
-	/* Tag domain that child domain prefers tasks go to siblings first */
-	sds->prefer_sibling = child && child->flags & SD_PREFER_SIBLING;
+	/*
+	 * Indicate that the child domain of the busiest group prefers tasks
+	 * go to a child's sibling domains first. NB the flags of a sched group
+	 * are those of the child domain.
+	 */
+	if (sds->busiest)
+		sds->prefer_sibling = !!(sds->busiest->flags & SD_PREFER_SIBLING);
 
 
 	if (env->sd->flags & SD_NUMA)
@@ -10440,7 +10421,10 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
 			goto out_balanced;
 	}
 
-	/* Try to move all excess tasks to child's sibling domain */
+	/*
+	 * Try to move all excess tasks to a sibling domain of the busiest
+	 * group's child domain.
+	 */
 	if (sds.prefer_sibling && local->group_type == group_has_spare &&
 	    busiest->sum_nr_running > local->sum_nr_running + 1)
 		goto force_balance;
@@ -10542,8 +10526,15 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 		    nr_running == 1)
 			continue;
 
-		/* Make sure we only pull tasks from a CPU of lower priority */
+		/*
+		 * Make sure we only pull tasks from a CPU of lower priority
+		 * when balancing between SMT siblings.
+		 *
+		 * If balancing between cores, let lower priority CPUs help
+		 * SMT cores with more than one busy sibling.
+		 */
 		if ((env->sd->flags & SD_ASYM_PACKING) &&
+		    sched_use_asym_prio(env->sd, i) &&
 		    sched_asym_prefer(i, env->dst_cpu) &&
 		    nr_running == 1)
 			continue;
@@ -10632,12 +10623,19 @@ static inline bool
 asym_active_balance(struct lb_env *env)
 {
 	/*
-	 * ASYM_PACKING needs to force migrate tasks from busy but
-	 * lower priority CPUs in order to pack all tasks in the
-	 * highest priority CPUs.
+	 * ASYM_PACKING needs to force migrate tasks from busy but lower
+	 * priority CPUs in order to pack all tasks in the highest priority
+	 * CPUs. When done between cores, do it only if the whole core if the
+	 * whole core is idle.
+	 *
+	 * If @env::src_cpu is an SMT core with busy siblings, let
+	 * the lower priority @env::dst_cpu help it. Do not follow
+	 * CPU priority.
 	 */
 	return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&
-	       sched_asym_prefer(env->dst_cpu, env->src_cpu);
+	       sched_use_asym_prio(env->sd, env->dst_cpu) &&
+	       (sched_asym_prefer(env->dst_cpu, env->src_cpu) ||
+		!sched_use_asym_prio(env->sd, env->src_cpu));
 }
 
 static inline bool
@@ -11371,9 +11369,13 @@ static void nohz_balancer_kick(struct rq *rq)
 		 * When ASYM_PACKING; see if there's a more preferred CPU
 		 * currently idle; in which case, kick the ILB to move tasks
 		 * around.
+		 *
+		 * When balancing betwen cores, all the SMT siblings of the
+		 * preferred CPU must be idle.
 		 */
 		for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) {
-			if (sched_asym_prefer(i, cpu)) {
+			if (sched_use_asym_prio(sd, i) &&
+			    sched_asym_prefer(i, cpu)) {
 				flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
 				goto unlock;
 			}