Merge branch 'sched/urgent' into sched/core, to pick up fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

4 files changed, 84 insertions, 15 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 625bc9897f62..ad97f3ba5ec5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1167,7 +1167,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 
 	if (task_cpu(p) != new_cpu) {
 		if (p->sched_class->migrate_task_rq)
-			p->sched_class->migrate_task_rq(p);
+			p->sched_class->migrate_task_rq(p, new_cpu);
 		p->se.nr_migrations++;
 		rseq_migrate(p);
 		perf_event_task_migrate(p);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 997ea7b839fa..91e4202b0634 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1607,7 +1607,7 @@ out:
 	return cpu;
 }
 
-static void migrate_task_rq_dl(struct task_struct *p)
+static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused)
 {
 	struct rq *rq;
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6bd142d19549..1d92ed2eca8b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1492,6 +1492,21 @@ struct task_numa_env {
 static void task_numa_assign(struct task_numa_env *env,
 			     struct task_struct *p, long imp)
 {
+	struct rq *rq = cpu_rq(env->dst_cpu);
+
+	/* Bail out if run-queue part of active NUMA balance. */
+	if (xchg(&rq->numa_migrate_on, 1))
+		return;
+
+	/*
+	 * Clear previous best_cpu/rq numa-migrate flag, since task now
+	 * found a better CPU to move/swap.
+	 */
+	if (env->best_cpu != -1) {
+		rq = cpu_rq(env->best_cpu);
+		WRITE_ONCE(rq->numa_migrate_on, 0);
+	}
+
 	if (env->best_task)
 		put_task_struct(env->best_task);
 	if (p)
@@ -1531,6 +1546,13 @@ static bool load_too_imbalanced(long src_load, long dst_load,
 }
 
 /*
+ * Maximum NUMA importance can be 1998 (2*999);
+ * SMALLIMP @ 30 would be close to 1998/64.
+ * Used to deter task migration.
+ */
+#define SMALLIMP	30
+
+/*
  * This checks if the overall compute and NUMA accesses of the system would
  * be improved if the source tasks was migrated to the target dst_cpu taking
  * into account that it might be best if task running on the dst_cpu should
@@ -1547,6 +1569,9 @@ static void task_numa_compare(struct task_numa_env *env,
 	long moveimp = imp;
 	int dist = env->dist;
 
+	if (READ_ONCE(dst_rq->numa_migrate_on))
+		return;
+
 	rcu_read_lock();
 	cur = task_rcu_dereference(&dst_rq->curr);
 	if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
@@ -1560,7 +1585,7 @@ static void task_numa_compare(struct task_numa_env *env,
 		goto unlock;
 
 	if (!cur) {
-		if (maymove || imp > env->best_imp)
+		if (maymove && moveimp >= env->best_imp)
 			goto assign;
 		else
 			goto unlock;
@@ -1603,16 +1628,22 @@ static void task_numa_compare(struct task_numa_env *env,
 			       task_weight(cur, env->dst_nid, dist);
 	}
 
-	if (imp <= env->best_imp)
-		goto unlock;
-
 	if (maymove && moveimp > imp && moveimp > env->best_imp) {
-		imp = moveimp - 1;
+		imp = moveimp;
 		cur = NULL;
 		goto assign;
 	}
 
 	/*
+	 * If the NUMA importance is less than SMALLIMP,
+	 * task migration might only result in ping pong
+	 * of tasks and also hurt performance due to cache
+	 * misses.
+	 */
+	if (imp < SMALLIMP || imp <= env->best_imp + SMALLIMP / 2)
+		goto unlock;
+
+	/*
 	 * In the overloaded case, try and keep the load balanced.
 	 */
 	load = task_h_load(env->p) - task_h_load(cur);
@@ -1688,6 +1719,7 @@ static int task_numa_migrate(struct task_struct *p)
 		.best_cpu = -1,
 	};
 	struct sched_domain *sd;
+	struct rq *best_rq;
 	unsigned long taskweight, groupweight;
 	int nid, ret, dist;
 	long taskimp, groupimp;
@@ -1783,20 +1815,17 @@ static int task_numa_migrate(struct task_struct *p)
 	if (env.best_cpu == -1)
 		return -EAGAIN;
 
-	/*
-	 * Reset the scan period if the task is being rescheduled on an
-	 * alternative node to recheck if the tasks is now properly placed.
-	 */
-	p->numa_scan_period = task_scan_start(p);
-
+	best_rq = cpu_rq(env.best_cpu);
 	if (env.best_task == NULL) {
 		ret = migrate_task_to(p, env.best_cpu);
+		WRITE_ONCE(best_rq->numa_migrate_on, 0);
 		if (ret != 0)
 			trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
 		return ret;
 	}
 
 	ret = migrate_swap(p, env.best_task, env.best_cpu, env.src_cpu);
+	WRITE_ONCE(best_rq->numa_migrate_on, 0);
 
 	if (ret != 0)
 		trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
@@ -2574,6 +2603,39 @@ void task_tick_numa(struct rq *rq, struct task_struct *curr)
 	}
 }
 
+static void update_scan_period(struct task_struct *p, int new_cpu)
+{
+	int src_nid = cpu_to_node(task_cpu(p));
+	int dst_nid = cpu_to_node(new_cpu);
+
+	if (!static_branch_likely(&sched_numa_balancing))
+		return;
+
+	if (!p->mm || !p->numa_faults || (p->flags & PF_EXITING))
+		return;
+
+	if (src_nid == dst_nid)
+		return;
+
+	/*
+	 * Allow resets if faults have been trapped before one scan
+	 * has completed. This is most likely due to a new task that
+	 * is pulled cross-node due to wakeups or load balancing.
+	 */
+	if (p->numa_scan_seq) {
+		/*
+		 * Avoid scan adjustments if moving to the preferred
+		 * node or if the task was not previously running on
+		 * the preferred node.
+		 */
+		if (dst_nid == p->numa_preferred_nid ||
+		    (p->numa_preferred_nid != -1 && src_nid != p->numa_preferred_nid))
+			return;
+	}
+
+	p->numa_scan_period = task_scan_start(p);
+}
+
 #else
 static void task_tick_numa(struct rq *rq, struct task_struct *curr)
 {
@@ -2587,6 +2649,10 @@ static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
 {
 }
 
+static inline void update_scan_period(struct task_struct *p, int new_cpu)
+{
+}
+
 #endif /* CONFIG_NUMA_BALANCING */
 
 static void
@@ -6280,7 +6346,7 @@ static void detach_entity_cfs_rq(struct sched_entity *se);
  * cfs_rq_of(p) references at time of call are still valid and identify the
  * previous CPU. The caller guarantees p->pi_lock or task_rq(p)->lock is held.
  */
-static void migrate_task_rq_fair(struct task_struct *p)
+static void migrate_task_rq_fair(struct task_struct *p, int new_cpu)
 {
 	/*
 	 * As blocked tasks retain absolute vruntime the migration needs to
@@ -6333,6 +6399,8 @@ static void migrate_task_rq_fair(struct task_struct *p)
 
 	/* We have migrated, no longer consider this task hot */
 	p->se.exec_start = 0;
+
+	update_scan_period(p, new_cpu);
 }
 
 static void task_dead_fair(struct task_struct *p)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3a4ef8f73f08..632804fa0b12 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -787,6 +787,7 @@ struct rq {
 #ifdef CONFIG_NUMA_BALANCING
 	unsigned int		nr_numa_running;
 	unsigned int		nr_preferred_running;
+	unsigned int		numa_migrate_on;
 #endif
 	#define CPU_LOAD_IDX_MAX 5
 	unsigned long		cpu_load[CPU_LOAD_IDX_MAX];
@@ -1531,7 +1532,7 @@ struct sched_class {
 
 #ifdef CONFIG_SMP
 	int  (*select_task_rq)(struct task_struct *p, int task_cpu, int sd_flag, int flags);
-	void (*migrate_task_rq)(struct task_struct *p);
+	void (*migrate_task_rq)(struct task_struct *p, int new_cpu);
 
 	void (*task_woken)(struct rq *this_rq, struct task_struct *task);