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Subject[PATCH 53/63] sched: numa: Decide whether to favour task or group weights based on swap candidate relationships
Date
From: Rik van Riel <riel@redhat.com>

This patch separately considers task and group affinities when searching
for swap candidates during task NUMA placement. If tasks are not part of
a group or the same group then the task weights are considered.
Otherwise the group weights are compared.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
kernel/sched/fair.c | 59 ++++++++++++++++++++++++++++++++---------------------
1 file changed, 36 insertions(+), 23 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cd1b862..60ca698 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1039,13 +1039,15 @@ static void task_numa_assign(struct task_numa_env *env,
* into account that it might be best if task running on the dst_cpu should
* be exchanged with the source task
*/
-static void task_numa_compare(struct task_numa_env *env, long imp)
+static void task_numa_compare(struct task_numa_env *env,
+ long taskimp, long groupimp)
{
struct rq *src_rq = cpu_rq(env->src_cpu);
struct rq *dst_rq = cpu_rq(env->dst_cpu);
struct task_struct *cur;
long dst_load, src_load;
long load;
+ long imp = (groupimp > 0) ? groupimp : taskimp;

rcu_read_lock();
cur = ACCESS_ONCE(dst_rq->curr);
@@ -1064,10 +1066,19 @@ 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_weight(cur, env->src_nid) +
- group_weight(cur, env->src_nid) -
- task_weight(cur, env->dst_nid) -
- group_weight(cur, env->dst_nid);
+ /*
+ * If dst and source tasks are in the same NUMA group, or not
+ * in any group then look only at task weights otherwise give
+ * priority to the group weights.
+ */
+ if (!cur->numa_group || !env->p->numa_group ||
+ cur->numa_group == env->p->numa_group) {
+ imp = taskimp + task_weight(cur, env->src_nid) -
+ task_weight(cur, env->dst_nid);
+ } else {
+ imp = groupimp + group_weight(cur, env->src_nid) -
+ group_weight(cur, env->dst_nid);
+ }
}

if (imp < env->best_imp)
@@ -1117,7 +1128,8 @@ unlock:
rcu_read_unlock();
}

-static void task_numa_find_cpu(struct task_numa_env *env, long imp)
+static void task_numa_find_cpu(struct task_numa_env *env,
+ long taskimp, long groupimp)
{
int cpu;

@@ -1127,7 +1139,7 @@ static void task_numa_find_cpu(struct task_numa_env *env, long imp)
continue;

env->dst_cpu = cpu;
- task_numa_compare(env, imp);
+ task_numa_compare(env, taskimp, groupimp);
}
}

@@ -1146,9 +1158,9 @@ static int task_numa_migrate(struct task_struct *p)
.best_cpu = -1
};
struct sched_domain *sd;
- unsigned long weight;
+ unsigned long taskweight, groupweight;
int nid, ret;
- long imp;
+ long taskimp, groupimp;

/*
* Pick the lowest SD_NUMA domain, as that would have the smallest
@@ -1163,15 +1175,17 @@ static int task_numa_migrate(struct task_struct *p)
env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
rcu_read_unlock();

- weight = task_weight(p, env.src_nid) + group_weight(p, env.src_nid);
+ taskweight = task_weight(p, env.src_nid);
+ groupweight = group_weight(p, env.src_nid);
update_numa_stats(&env.src_stats, env.src_nid);
env.dst_nid = p->numa_preferred_nid;
- imp = task_weight(p, env.dst_nid) + group_weight(p, env.dst_nid) - weight;
+ taskimp = task_weight(p, env.dst_nid) - taskweight;
+ groupimp = group_weight(p, env.dst_nid) - groupweight;
update_numa_stats(&env.dst_stats, env.dst_nid);

/* If the preferred nid has capacity, try to use it. */
if (env.dst_stats.has_capacity)
- task_numa_find_cpu(&env, imp);
+ task_numa_find_cpu(&env, taskimp, groupimp);

/* No space available on the preferred nid. Look elsewhere. */
if (env.best_cpu == -1) {
@@ -1180,13 +1194,14 @@ static int task_numa_migrate(struct task_struct *p)
continue;

/* Only consider nodes where both task and groups benefit */
- imp = task_weight(p, nid) + group_weight(p, nid) - weight;
- if (imp < 0)
+ taskimp = task_weight(p, nid) - taskweight;
+ groupimp = group_weight(p, nid) - groupweight;
+ if (taskimp < 0 && groupimp < 0)
continue;

env.dst_nid = nid;
update_numa_stats(&env.dst_stats, env.dst_nid);
- task_numa_find_cpu(&env, imp);
+ task_numa_find_cpu(&env, taskimp, groupimp);
}
}

@@ -4632,10 +4647,9 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
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))
+ /* If both task and group weight improve, this move is a winner. */
+ if (task_weight(p, dst_nid) > task_weight(p, src_nid) &&
+ group_weight(p, dst_nid) > group_weight(p, src_nid))
return true;

return false;
@@ -4662,10 +4676,9 @@ static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
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))
+ /* If either task or group weight get worse, don't do it. */
+ if (task_weight(p, dst_nid) < task_weight(p, src_nid) ||
+ group_weight(p, dst_nid) < group_weight(p, src_nid))
return true;

return false;
--
1.8.1.4


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