linux-kernel - [PATCH 15/15] sched: Favour moving tasks towards nodes that incurred more faults

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Date:	Sat,  6 Jul 2013 00:09:02 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
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>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 15/15] sched: Favour moving tasks towards nodes that incurred more faults

The scheduler already favours moving tasks towards its preferred node but
does nothing special if the destination node is anything else. This patch
favours moving tasks towards a destination node if more NUMA hinting faults
were recorded on it. Similarly if migrating to a destination node would
degrade locality based on NUMA hinting faults then it will be resisted.

Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 kernel/sched/fair.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c303ba6..1a4af96 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4069,24 +4069,65 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
 }
 
 #ifdef CONFIG_NUMA_BALANCING
-/* Returns true if the destination node has incurred more faults */
-static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
+
+static bool migrate_locality_prepare(struct task_struct *p, struct lb_env *env,
+			int *src_nid, int *dst_nid,
+			unsigned long *src_faults, unsigned long *dst_faults)
 {
-	int src_nid, dst_nid;
+	int priv;
 
 	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
 		return false;
 
-	src_nid = cpu_to_node(env->src_cpu);
-	dst_nid = cpu_to_node(env->dst_cpu);
+	*src_nid = cpu_to_node(env->src_cpu);
+	*dst_nid = cpu_to_node(env->dst_cpu);
 
-	if (src_nid == dst_nid ||
+	if (*src_nid == *dst_nid ||
 	    p->numa_migrate_seq >= sysctl_numa_balancing_settle_count)
 		return false;
 
+	/* Calculate private/shared faults on the two nodes */
+	*src_faults = 0;
+	*dst_faults = 0;
+	for (priv = 0; priv < 2; priv++) {
+		*src_faults += p->numa_faults[task_faults_idx(*src_nid, priv)];
+		*dst_faults += p->numa_faults[task_faults_idx(*dst_nid, priv)];
+	}
+
+	return true;
+}
+
+/* Returns true if the destination node has incurred more faults */
+static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
+{
+	int src_nid, dst_nid;
+	unsigned long src, dst;
+
+	if (!migrate_locality_prepare(p, env, &src_nid, &dst_nid, &src, &dst))
+		return false;
+
+	/* Move towards node if it is the preferred node */
 	if (p->numa_preferred_nid == dst_nid)
 		return true;
 
+	/* Move towards node if there were more NUMA hinting faults recorded */
+	if (dst > src)
+		return true;
+
+	return false;
+}
+
+static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
+{
+	int src_nid, dst_nid;
+	unsigned long src, dst;
+
+	if (!migrate_locality_prepare(p, env, &src_nid, &dst_nid, &src, &dst))
+		return false;
+
+	if (src > dst)
+		return true;
+
 	return false;
 }
 #else
@@ -4095,6 +4136,14 @@ static inline bool migrate_improves_locality(struct task_struct *p,
 {
 	return false;
 }
+
+
+static inline bool migrate_degrades_locality(struct task_struct *p,
+					     struct lb_env *env)
+{
+	return false;
+}
+
 #endif
 
 /*
@@ -4150,6 +4199,8 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 	 * 3) too many balance attempts have failed.
 	 */
 	tsk_cache_hot = task_hot(p, env->src_rq->clock_task, env->sd);
+	if (!tsk_cache_hot)
+		tsk_cache_hot = migrate_degrades_locality(p, env);
 
 	if (migrate_improves_locality(p, env)) {
 #ifdef CONFIG_SCHEDSTATS
-- 
1.8.1.4

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