sched: Validate assumptions in sched_init_numa()

Add some code to validate assumptions we're making and output
warnings if they are not.

If this trigger we want to know about it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alex Shi <lkml.alex@gmail.com>
Link: http://lkml.kernel.org/n/tip-6uc3wk5s9udxtdl9cnku0vtt@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 80 insertions, 19 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 725ee7c1c8cf..2bdd17616437 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5556,15 +5556,20 @@ static cpumask_var_t sched_domains_tmpmask; /* sched_domains_mutex */
 
 #ifdef CONFIG_SCHED_DEBUG
 
-static __read_mostly int sched_domain_debug_enabled;
+static __read_mostly int sched_debug_enabled;
 
-static int __init sched_domain_debug_setup(char *str)
+static int __init sched_debug_setup(char *str)
 {
-        sched_domain_debug_enabled = 1;
+        sched_debug_enabled = 1;
 
         return 0;
 }
-early_param("sched_debug", sched_domain_debug_setup);
+early_param("sched_debug", sched_debug_setup);
+
+static inline bool sched_debug(void)
+{
+        return sched_debug_enabled;
+}
 
 static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
                                   struct cpumask *groupmask)
@@ -5657,7 +5662,7 @@ static void sched_domain_debug(struct sched_domain *sd, int cpu)
 {
         int level = 0;
 
-        if (!sched_domain_debug_enabled)
+        if (!sched_debug_enabled)
                 return;
 
         if (!sd) {
@@ -5678,6 +5683,10 @@ static void sched_domain_debug(struct sched_domain *sd, int cpu)
 }
 #else /* !CONFIG_SCHED_DEBUG */
 # define sched_domain_debug(sd, cpu) do { } while (0)
+static inline bool sched_debug(void)
+{
+        return false;
+}
 #endif /* CONFIG_SCHED_DEBUG */
 
 static int sd_degenerate(struct sched_domain *sd)
@@ -6373,7 +6382,6 @@ static struct sched_domain_topology_level *sched_domain_topology = default_topol
 #ifdef CONFIG_NUMA
 
 static int sched_domains_numa_levels;
-static int sched_domains_numa_scale;
 static int *sched_domains_numa_distance;
 static struct cpumask ***sched_domains_numa_masks;
 static int sched_domains_curr_level;
@@ -6438,6 +6446,42 @@ static const struct cpumask *sd_numa_mask(int cpu)
         return sched_domains_numa_masks[sched_domains_curr_level][cpu_to_node(cpu)];
 }
 
+static void sched_numa_warn(const char *str)
+{
+        static int done = false;
+        int i,j;
+
+        if (done)
+                return;
+
+        done = true;
+
+        printk(KERN_WARNING "ERROR: %s\n\n", str);
+
+        for (i = 0; i < nr_node_ids; i++) {
+                printk(KERN_WARNING "  ");
+                for (j = 0; j < nr_node_ids; j++)
+                        printk(KERN_CONT "%02d ", node_distance(i,j));
+                printk(KERN_CONT "\n");
+        }
+        printk(KERN_WARNING "\n");
+}
+
+static bool find_numa_distance(int distance)
+{
+        int i;
+
+        if (distance == node_distance(0, 0))
+                return true;
+
+        for (i = 0; i < sched_domains_numa_levels; i++) {
+                if (sched_domains_numa_distance[i] == distance)
+                        return true;
+        }
+
+        return false;
+}
+
 static void sched_init_numa(void)
 {
         int next_distance, curr_distance = node_distance(0, 0);
@@ -6445,7 +6489,6 @@ static void sched_init_numa(void)
         int level = 0;
         int i, j, k;
 
-        sched_domains_numa_scale = curr_distance;
         sched_domains_numa_distance = kzalloc(sizeof(int) * nr_node_ids, GFP_KERNEL);
         if (!sched_domains_numa_distance)
                 return;
@@ -6456,23 +6499,41 @@ static void sched_init_numa(void)
          *
          * Assumes node_distance(0,j) includes all distances in
          * node_distance(i,j) in order to avoid cubic time.
-         *
-         * XXX: could be optimized to O(n log n) by using sort()
          */
         next_distance = curr_distance;
         for (i = 0; i < nr_node_ids; i++) {
                 for (j = 0; j < nr_node_ids; j++) {
-                        int distance = node_distance(0, j);
-                        if (distance > curr_distance &&
-                                        (distance < next_distance ||
-                                         next_distance == curr_distance))
-                                next_distance = distance;
+                        for (k = 0; k < nr_node_ids; k++) {
+                                int distance = node_distance(i, k);
+
+                                if (distance > curr_distance &&
+                                    (distance < next_distance ||
+                                     next_distance == curr_distance))
+                                        next_distance = distance;
+
+                                /*
+                                 * While not a strong assumption it would be nice to know
+                                 * about cases where if node A is connected to B, B is not
+                                 * equally connected to A.
+                                 */
+                                if (sched_debug() && node_distance(k, i) != distance)
+                                        sched_numa_warn("Node-distance not symmetric");
+
+                                if (sched_debug() && i && !find_numa_distance(distance))
+                                        sched_numa_warn("Node-0 not representative");
+                        }
+                        if (next_distance != curr_distance) {
+                                sched_domains_numa_distance[level++] = next_distance;
+                                sched_domains_numa_levels = level;
+                                curr_distance = next_distance;
+                        } else break;
                 }
-                if (next_distance != curr_distance) {
-                        sched_domains_numa_distance[level++] = next_distance;
-                        sched_domains_numa_levels = level;
-                        curr_distance = next_distance;
-                } else break;
+
+                /*
+                 * In case of sched_debug() we verify the above assumption.
+                 */
+                if (!sched_debug())
+                        break;
         }
         /*
          * 'level' contains the number of unique distances, excluding the