sched/numa: Use group fault statistics in numa placement

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: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-50-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8563e3dd5c0fcae385b3f23f88b3b479f4fafd43..724482200b83e640667cc7a392bda015ef05b72d 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1356,6 +1356,7 @@ 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 35661b8afb4e042b16ad79fc9b718df74089c94d..4c40e13310e9527534da84a6d3e46b357db3ea4e 100644 (file)
--- 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;
        }
 
        /*
@@ -4572,12 +4651,17 @@ 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;
@@ -4597,11 +4681,17 @@ 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;