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Subject[PATCH 49/63] sched: numa: use group fault statistics in numa placement
Date
This patch uses the fraction of faults on a particular node for both task
and group, to figure out the best node to place a task. If the task and
group statistics disagree on what the preferred node should be then a full
rescan will select the node with the best combined weight.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
include/linux/sched.h | 1 +
kernel/sched/fair.c | 124 +++++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 108 insertions(+), 17 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4f51ceb..46fb36a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1347,6 +1347,7 @@ struct task_struct {
* The values remain static for the duration of a PTE scan
*/
unsigned long *numa_faults;
+ unsigned long total_numa_faults;

/*
* numa_faults_buffer records faults per node during the current
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 896cf87..801fc74 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -897,6 +897,7 @@ struct numa_group {
struct list_head task_list;

struct rcu_head rcu;
+ atomic_long_t total_faults;
atomic_long_t faults[0];
};

@@ -919,6 +920,51 @@ static inline unsigned long task_faults(struct task_struct *p, int nid)
p->numa_faults[task_faults_idx(nid, 1)];
}

+static inline unsigned long group_faults(struct task_struct *p, int nid)
+{
+ if (!p->numa_group)
+ return 0;
+
+ return atomic_long_read(&p->numa_group->faults[2*nid]) +
+ atomic_long_read(&p->numa_group->faults[2*nid+1]);
+}
+
+/*
+ * These return the fraction of accesses done by a particular task, or
+ * task group, on a particular numa node. The group weight is given a
+ * larger multiplier, in order to group tasks together that are almost
+ * evenly spread out between numa nodes.
+ */
+static inline unsigned long task_weight(struct task_struct *p, int nid)
+{
+ unsigned long total_faults;
+
+ if (!p->numa_faults)
+ return 0;
+
+ total_faults = p->total_numa_faults;
+
+ if (!total_faults)
+ return 0;
+
+ return 1000 * task_faults(p, nid) / total_faults;
+}
+
+static inline unsigned long group_weight(struct task_struct *p, int nid)
+{
+ unsigned long total_faults;
+
+ if (!p->numa_group)
+ return 0;
+
+ total_faults = atomic_long_read(&p->numa_group->total_faults);
+
+ if (!total_faults)
+ return 0;
+
+ return 1200 * group_faults(p, nid) / total_faults;
+}
+
static unsigned long weighted_cpuload(const int cpu);
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);
@@ -1018,8 +1064,10 @@ static void task_numa_compare(struct task_numa_env *env, long imp)
if (!cpumask_test_cpu(env->src_cpu, tsk_cpus_allowed(cur)))
goto unlock;

- imp += task_faults(cur, env->src_nid) -
- task_faults(cur, env->dst_nid);
+ imp += task_weight(cur, env->src_nid) +
+ group_weight(cur, env->src_nid) -
+ task_weight(cur, env->dst_nid) -
+ group_weight(cur, env->dst_nid);
}

if (imp < env->best_imp)
@@ -1098,7 +1146,7 @@ static int task_numa_migrate(struct task_struct *p)
.best_cpu = -1
};
struct sched_domain *sd;
- unsigned long faults;
+ unsigned long weight;
int nid, ret;
long imp;

@@ -1115,10 +1163,10 @@ static int task_numa_migrate(struct task_struct *p)
env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
rcu_read_unlock();

- faults = task_faults(p, env.src_nid);
+ weight = task_weight(p, env.src_nid) + group_weight(p, env.src_nid);
update_numa_stats(&env.src_stats, env.src_nid);
env.dst_nid = p->numa_preferred_nid;
- imp = task_faults(env.p, env.dst_nid) - faults;
+ imp = task_weight(p, env.dst_nid) + group_weight(p, env.dst_nid) - weight;
update_numa_stats(&env.dst_stats, env.dst_nid);

/* If the preferred nid has capacity, try to use it. */
@@ -1131,8 +1179,8 @@ static int task_numa_migrate(struct task_struct *p)
if (nid == env.src_nid || nid == p->numa_preferred_nid)
continue;

- /* Only consider nodes that recorded more faults */
- imp = task_faults(env.p, nid) - faults;
+ /* Only consider nodes where both task and groups benefit */
+ imp = task_weight(p, nid) + group_weight(p, nid) - weight;
if (imp < 0)
continue;

@@ -1183,8 +1231,8 @@ static void numa_migrate_preferred(struct task_struct *p)

static void task_numa_placement(struct task_struct *p)
{
- int seq, nid, max_nid = -1;
- unsigned long max_faults = 0;
+ int seq, nid, max_nid = -1, max_group_nid = -1;
+ unsigned long max_faults = 0, max_group_faults = 0;

seq = ACCESS_ONCE(p->mm->numa_scan_seq);
if (p->numa_scan_seq == seq)
@@ -1195,7 +1243,7 @@ static void task_numa_placement(struct task_struct *p)

/* Find the node with the highest number of faults */
for_each_online_node(nid) {
- unsigned long faults = 0;
+ unsigned long faults = 0, group_faults = 0;
int priv, i;

for (priv = 0; priv < 2; priv++) {
@@ -1211,9 +1259,12 @@ static void task_numa_placement(struct task_struct *p)

faults += p->numa_faults[i];
diff += p->numa_faults[i];
+ p->total_numa_faults += diff;
if (p->numa_group) {
/* safe because we can only change our own group */
atomic_long_add(diff, &p->numa_group->faults[i]);
+ atomic_long_add(diff, &p->numa_group->total_faults);
+ group_faults += atomic_long_read(&p->numa_group->faults[i]);
}
}

@@ -1221,6 +1272,27 @@ static void task_numa_placement(struct task_struct *p)
max_faults = faults;
max_nid = nid;
}
+
+ if (group_faults > max_group_faults) {
+ max_group_faults = group_faults;
+ max_group_nid = nid;
+ }
+ }
+
+ /*
+ * If the preferred task and group nids are different,
+ * iterate over the nodes again to find the best place.
+ */
+ if (p->numa_group && max_nid != max_group_nid) {
+ unsigned long weight, max_weight = 0;
+
+ for_each_online_node(nid) {
+ weight = task_weight(p, nid) + group_weight(p, nid);
+ if (weight > max_weight) {
+ max_weight = weight;
+ max_nid = nid;
+ }
+ }
}

/* Preferred node as the node with the most faults */
@@ -1276,6 +1348,8 @@ static void task_numa_group(struct task_struct *p, int cpupid)
for (i = 0; i < 2*nr_node_ids; i++)
atomic_long_set(&grp->faults[i], p->numa_faults[i]);

+ atomic_long_set(&grp->total_faults, p->total_numa_faults);
+
list_add(&p->numa_entry, &grp->task_list);
grp->nr_tasks++;
rcu_assign_pointer(p->numa_group, grp);
@@ -1323,6 +1397,8 @@ unlock:
atomic_long_sub(p->numa_faults[i], &my_grp->faults[i]);
atomic_long_add(p->numa_faults[i], &grp->faults[i]);
}
+ atomic_long_sub(p->total_numa_faults, &my_grp->total_faults);
+ atomic_long_add(p->total_numa_faults, &grp->total_faults);

double_lock(&my_grp->lock, &grp->lock);

@@ -1347,6 +1423,8 @@ void task_numa_free(struct task_struct *p)
for (i = 0; i < 2*nr_node_ids; i++)
atomic_long_sub(p->numa_faults[i], &grp->faults[i]);

+ atomic_long_sub(p->total_numa_faults, &grp->total_faults);
+
spin_lock(&grp->lock);
list_del(&p->numa_entry);
grp->nr_tasks--;
@@ -1385,6 +1463,7 @@ void task_numa_fault(int last_cpupid, int node, int pages, int flags)

BUG_ON(p->numa_faults_buffer);
p->numa_faults_buffer = p->numa_faults + (2 * nr_node_ids);
+ p->total_numa_faults = 0;
}

/*
@@ -4525,12 +4604,17 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
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)
+ if (src_nid == dst_nid)
return false;

- if (dst_nid == p->numa_preferred_nid ||
- task_faults(p, dst_nid) > task_faults(p, src_nid))
+ /* Always encourage migration to the preferred node. */
+ if (dst_nid == p->numa_preferred_nid)
+ return true;
+
+ /* After the task has settled, check if the new node is better. */
+ if (p->numa_migrate_seq >= sysctl_numa_balancing_settle_count &&
+ task_weight(p, dst_nid) + group_weight(p, dst_nid) >
+ task_weight(p, src_nid) + group_weight(p, src_nid))
return true;

return false;
@@ -4550,11 +4634,17 @@ static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
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)
+ if (src_nid == dst_nid)
return false;

- if (task_faults(p, dst_nid) < task_faults(p, src_nid))
+ /* Migrating away from the preferred node is always bad. */
+ if (src_nid == p->numa_preferred_nid)
+ return true;
+
+ /* After the task has settled, check if the new node is worse. */
+ if (p->numa_migrate_seq >= sysctl_numa_balancing_settle_count &&
+ task_weight(p, dst_nid) + group_weight(p, dst_nid) <
+ task_weight(p, src_nid) + group_weight(p, src_nid))
return true;

return false;
--
1.8.1.4


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