linux-kernel - [tip:sched/core] sched/numa: Resist moving tasks towards nodes with fewer hinting faults

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Date:	Wed, 9 Oct 2013 10:27:42 -0700
From:	tip-bot for Mel Gorman <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	peterz@...radead.org, hannes@...xchg.org, riel@...hat.com,
	aarcange@...hat.com, srikar@...ux.vnet.ibm.com, mgorman@...e.de,
	tglx@...utronix.de
Subject: [tip:sched/core] sched/numa:
  Resist moving tasks towards nodes with fewer hinting faults

Commit-ID:  7a0f308337d11fd5caa9f845c6d08cc5d6067988
Gitweb:     http://git.kernel.org/tip/7a0f308337d11fd5caa9f845c6d08cc5d6067988
Author:     Mel Gorman <mgorman@...e.de>
AuthorDate: Mon, 7 Oct 2013 11:29:01 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 9 Oct 2013 12:40:27 +0200

sched/numa: Resist moving tasks towards nodes with fewer hinting faults

Just as "sched: Favour moving tasks towards the preferred node" favours
moving tasks towards nodes with a higher number of recorded NUMA hinting
faults, this patch resists moving tasks towards nodes with lower faults.

Signed-off-by: Mel Gorman <mgorman@...e.de>
Reviewed-by: Rik van Riel <riel@...hat.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-24-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c     | 33 +++++++++++++++++++++++++++++++++
 kernel/sched/features.h |  8 ++++++++
 2 files changed, 41 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6ffddca..8943124 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4107,12 +4107,43 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
 
 	return false;
 }
+
+
+static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
+{
+	int src_nid, dst_nid;
+
+	if (!sched_feat(NUMA) || !sched_feat(NUMA_RESIST_LOWER))
+		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 (p->numa_faults[dst_nid] < p->numa_faults[src_nid])
+		return true;
+
+	return false;
+}
+
 #else
 static inline bool migrate_improves_locality(struct task_struct *p,
 					     struct lb_env *env)
 {
 	return false;
 }
+
+static inline bool migrate_degrades_locality(struct task_struct *p,
+					     struct lb_env *env)
+{
+	return false;
+}
 #endif
 
 /*
@@ -4177,6 +4208,8 @@ 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, 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
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index d9278ce..5716929 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -74,4 +74,12 @@ SCHED_FEAT(NUMA,	false)
  * balancing.
  */
 SCHED_FEAT(NUMA_FAVOUR_HIGHER, true)
+
+/*
+ * NUMA_RESIST_LOWER will resist moving tasks towards nodes where a
+ * lower number of hinting faults have been recorded. As this has
+ * the potential to prevent a task ever migrating to a new node
+ * due to CPU overload it is disabled by default.
+ */
+SCHED_FEAT(NUMA_RESIST_LOWER, false)
 #endif
--
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