Date:	Tue, 2 Jul 2013 20:15:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/8] sched: Reschedule task on preferred NUMA node once
 selected



Something like this should avoid tasks being lumped back onto one node..

Compile tested only, need food.

---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1037,6 +1037,23 @@ struct migration_arg {
 
 static int migration_cpu_stop(void *data);
 
+#ifdef CONFIG_NUMA_BALANCING
+int migrate_curr_to(int cpu)
+{
+	struct task_struct *p = current;
+	struct migration_arg arg = { p, cpu };
+	int curr_cpu = task_cpu(p);
+
+	if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(p)))
+		return -EINVAL;
+
+	if (curr_cpu == cpu)
+		return 0;
+
+	return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
+}
+#endif
+
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *
@@ -5183,30 +5200,6 @@ enum s_alloc {
 
 struct sched_domain_topology_level;
 
-#ifdef CONFIG_NUMA_BALANCING
-
-/* Set a tasks preferred NUMA node and reschedule to it */
-void sched_setnuma(struct task_struct *p, int nid, int idlest_cpu)
-{
-	int curr_cpu = task_cpu(p);
-	struct migration_arg arg = { p, idlest_cpu };
-
-	p->numa_preferred_nid = nid;
-	p->numa_migrate_seq = 0;
-
-	/* Do not reschedule if already running on the target CPU */
-	if (idlest_cpu == curr_cpu)
-		return;
-
-	/* Ensure the target CPU is eligible */
-	if (!cpumask_test_cpu(idlest_cpu, tsk_cpus_allowed(p)))
-		return;
-
-	/* Move current running task to idlest CPU on preferred node */
-	stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
-}
-#endif /* CONFIG_NUMA_BALANCING */
-
 typedef struct sched_domain *(*sched_domain_init_f)(struct sched_domain_topology_level *tl, int cpu);
 typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);
 
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -838,34 +838,76 @@ unsigned int sysctl_numa_balancing_scan_
  */
 unsigned int sysctl_numa_balancing_settle_count __read_mostly = 3;
 
-static unsigned long weighted_cpuload(const int cpu);
 
-static int find_idlest_cpu_node(int this_cpu, int nid)
-{
-	unsigned long load, min_load = ULONG_MAX;
-	int i, idlest_cpu = this_cpu;
+static unsigned long source_load(int cpu, int type);
+static unsigned long target_load(int cpu, int type);
+static unsigned long power_of(int cpu);
+static long effective_load(struct task_group *tg, int cpu, long wl, long wg);
+
+static int task_numa_find_cpu(struct task_struct *p)
+{
+	int nid = p->numa_preferred_nid;
+	int node_cpu = cpumask_first(cpumask_of_node(nid));
+	int cpu, src_cpu = task_cpu(p), dst_cpu = src_cpu;
+	unsigned long src_load, dst_load, min_load = ULONG_MAX;
+	struct task_group *tg = task_group(p);
+	s64 src_eff_load, dst_eff_load;
+	struct sched_domain *sd;
+	unsigned long weight;
+	bool balanced;
+	int idx;
 
-	BUG_ON(cpu_to_node(this_cpu) == nid);
+	rcu_read_lock();
+	for_each_domain(src_cpu, sd) {
+		if (cpumask_test_cpu(src_cpu,  sched_domain_span(sd)) &&
+		    cpumask_test_cpu(node_cpu, sched_domain_span(sd)))
+			break;
+	}
 
-	for_each_cpu(i, cpumask_of_node(nid)) {
-		load = weighted_cpuload(i);
+	if (WARN_ON_ONCE(!sd)) {
+		rcu_read_unlock();
+		return dst_cpu;
+	}
 
-		if (load < min_load) {
-			struct task_struct *p;
-			struct rq *rq = cpu_rq(i);
+	/*
+	 * XXX the below is mostly nicked from wake_affine(); we should
+	 * see about sharing a bit if at all possible; also it might want
+	 * some per entity weight love.
+	 */
 
-			/* Do not preempt a task running on its preferred node */
-			raw_spin_lock_irq(&rq->lock);
-			p = rq->curr;
-			if (p->numa_preferred_nid != nid) {
-				min_load = load;
-				idlest_cpu = i;
-			}
-			raw_spin_unlock_irq(&rq->lock);
+	idx = sd->busy_idx; /* XXX do we want another idx? */
+	weight = p->se.load.weight;
+
+	src_load = source_load(src_cpu, idx);
+
+	src_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
+	src_eff_load *= power_of(src_cpu);
+	src_eff_load *= src_load + effective_load(tg, src_cpu, -weight, -weight);
+
+	rcu_read_unlock();
+
+	for_each_cpu(cpu, cpumask_of_node(nid)) {
+		dst_load = target_load(cpu, idx);
+
+		dst_eff_load = 100;
+		dst_eff_load *= power_of(cpu);
+		dst_eff_load *= dst_load + effective_load(tg, cpu, weight, weight);
+
+		balanced = (dst_eff_load <= src_eff_load);
+
+		/*
+		 * If the dst cpu wasn't idle; don't allow imbalances
+		 */
+		if (dst_load && !balanced)
+			continue;
+
+		if (dst_load < min_load) {
+			min_load = dst_load;
+			dst_cpu = cpu;
 		}
 	}
 
-	return idlest_cpu;
+	return dst_cpu;
 }
 
 static inline int task_faults_idx(int nid, int priv)
@@ -915,29 +957,31 @@ static void task_numa_placement(struct t
 	 * the working set placement.
 	 */
 	if (max_faults && max_nid != p->numa_preferred_nid) {
-		int preferred_cpu;
 		int old_migrate_seq = p->numa_migrate_seq;
 
-		/*
-		 * If the task is not on the preferred node then find the most
-		 * idle CPU to migrate to.
-		 */
-		preferred_cpu = task_cpu(p);
-		if (cpu_to_node(preferred_cpu) != max_nid)
-			preferred_cpu = find_idlest_cpu_node(preferred_cpu,
-							     max_nid);
-
-		sched_setnuma(p, max_nid, preferred_cpu);
+		p->numa_preferred_nid = max_nid;
+		p->numa_migrate_seq = 0;
 
 		/*
 		 * If preferred nodes changes frequently then the scan rate
 		 * will be continually high. Mitigate this by increaseing the
 		 * scan rate only if the task was settled.
 		 */
-		if (old_migrate_seq >= sysctl_numa_balancing_settle_count)
-			p->numa_scan_period = max(p->numa_scan_period >> 1,
-					sysctl_numa_balancing_scan_period_min);
+		if (old_migrate_seq >= sysctl_numa_balancing_settle_count) {
+			p->numa_scan_period =
+				max(p->numa_scan_period >> 1,
+				    sysctl_numa_balancing_scan_period_min);
+		}
 	}
+
+	if (p->numa_preferred_nid == numa_node_id())
+		return;
+
+	/*
+	 * If the task is not on the preferred node then find the most
+	 * idle CPU to migrate to.
+	 */
+	migrate_curr_to(task_numa_find_cpu(p));
 }
 
 /*
@@ -956,7 +1000,7 @@ void task_numa_fault(int last_nid, int n
 		int size = sizeof(*p->numa_faults) * 2 * nr_node_ids;
 
 		/* numa_faults and numa_faults_buffer share the allocation */
-		p->numa_faults = kzalloc(size * 4, GFP_KERNEL);
+		p->numa_faults = kzalloc(size * 2, GFP_KERNEL);
 		if (!p->numa_faults)
 			return;
 
@@ -968,9 +1012,10 @@ void task_numa_fault(int last_nid, int n
 	 * If pages are properly placed (did not migrate) then scan slower.
 	 * This is reset periodically in case of phase changes
 	 */
-        if (!migrated)
+        if (!migrated) {
 		p->numa_scan_period = min(sysctl_numa_balancing_scan_period_max,
 			p->numa_scan_period + jiffies_to_msecs(10));
+	}
 
 	task_numa_placement(p);
 
@@ -3245,8 +3290,7 @@ static long effective_load(struct task_g
 }
 #else
 
-static inline unsigned long effective_load(struct task_group *tg, int cpu,
-		unsigned long wl, unsigned long wg)
+static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 {
 	return wl;
 }
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -555,7 +555,7 @@ static inline u64 rq_clock_task(struct r
 }
 
 #ifdef CONFIG_NUMA_BALANCING
-extern void sched_setnuma(struct task_struct *p, int nid, int idlest_cpu);
+extern int migrate_curr_to(int cpu);
 static inline void task_numa_free(struct task_struct *p)
 {
 	kfree(p->numa_faults);



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