[PATCH] sched, numa: migrates_degrades_locality()

[Peter Zijlstra]

Subject: sched, numa: migrates_degrades_locality()
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon Jul 22 14:02:54 CEST 2013

It just makes heaps of sense; so add it and make both it and
migrate_improve_locality() a sched_feat().

Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-fwfjk3f8a29o3zx03h1ejb0y@xxxxxxxxxxxxxx
---
 kernel/sched/fair.c     |   35 +++++++++++++++++++++++++++++++++--
 kernel/sched/features.h |    2 ++
 2 files changed, 35 insertions(+), 2 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4323,7 +4323,7 @@ static bool migrate_improves_locality(st
 {
 	int src_nid, dst_nid;
 
-	if (!sched_feat(NUMA_BALANCE))
+	if (!sched_feat(NUMA_BALANCE) || !sched_feat(NUMA_FAULTS_UP))
 		return false;
 
 	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
@@ -4336,7 +4336,30 @@ static bool migrate_improves_locality(st
 	    p->numa_migrate_seq >= sysctl_numa_balancing_settle_count)
 		return false;
 
-	if (p->numa_preferred_nid == dst_nid)
+	if (task_faults(p, dst_nid) > task_faults(p, src_nid))
+		return true;
+
+	return false;
+}
+
+static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
+{
+	int src_nid, dst_nid;
+
+	if (!sched_feat(NUMA_BALANCE) || !sched_feat(NUMA_FAULTS_DOWN))
+		return false;
+
+	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);
+
+	if (src_nid == dst_nid ||
+	    p->numa_migrate_seq >= sysctl_numa_balancing_settle_count)
+		return false;
+
+	if (task_faults(p, dst_nid) < task_faults(p, src_nid))
 		return true;
 
 	return false;
@@ -4347,6 +4370,12 @@ static inline bool migrate_improves_loca
 {
 	return false;
 }
+
+static inline bool migrate_degrades_locality(struct task_struct *p,
+					     struct lb_env *env)
+{
+	return false;
+}
 #endif
 
 /*
@@ -4409,6 +4438,8 @@ int can_migrate_task(struct task_struct
 	 * 3) too many balance attempts have failed.
 	 */
 	tsk_cache_hot = task_hot(p, rq_clock_task(env->src_rq), env->sd);
+	if (!tsk_cache_hot)
+		tsk_cache_hot = migrate_degrades_locality(p, env);
 
 	if (migrate_improves_locality(p, env)) {
 #ifdef CONFIG_SCHEDSTATS
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -70,4 +70,6 @@ SCHED_FEAT(LB_MIN, false)
 SCHED_FEAT(NUMA,	false)
 SCHED_FEAT(NUMA_FORCE,	false)
 SCHED_FEAT(NUMA_BALANCE, true)
+SCHED_FEAT(NUMA_FAULTS_UP, true)
+SCHED_FEAT(NUMA_FAULTS_DOWN, false)
 #endif
--
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