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Subject[PATCH 19/27] sched: Resist moving tasks towards nodes with fewer hinting faults
Date
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.

[mgorman@suse.de: changelog]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
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 dad3ae9..f828803 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4057,12 +4057,43 @@ 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

/*
@@ -4125,6 +4156,8 @@ 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
--
1.8.1.4


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