[PATCH 5.14 028/334] sched/topology: Skip updating masks for non-online nodes

Greg Kroah-Hartman
2021-09-13T14:26:09Z

From: Valentin Schneider <valentin.schneider@arm.com>

[ Upstream commit 0083242c93759dde353a963a90cb351c5c283379 ]

The scheduler currently expects NUMA node distances to be stable from
init onwards, and as a consequence builds the related data structures
once-and-for-all at init (see sched_init_numa()).

Unfortunately, on some architectures node distance is unreliable for
offline nodes and may very well change upon onlining.

Skip over offline nodes during sched_init_numa(). Track nodes that have
been onlined at least once, and trigger a build of a node's NUMA masks
when it is first onlined post-init.

Reported-by: Geetika Moolchandani <Geetika.Moolchandani1@ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210818074333.48645-1-srikar@linux.vnet.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sched/topology.c | 65 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index b77ad49dc14f..4e8698e62f07 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1482,6 +1482,8 @@ int sched_max_numa_distance;
static int *sched_domains_numa_distance;
static struct cpumask ***sched_domains_numa_masks;
int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE;
+
+static unsigned long __read_mostly *sched_numa_onlined_nodes;
#endif

/*
@@ -1833,6 +1835,16 @@ void sched_init_numa(void)
sched_domains_numa_masks[i][j] = mask;

for_each_node(k) {
+ /*
+ * Distance information can be unreliable for
+ * offline nodes, defer building the node
+ * masks to its bringup.
+ * This relies on all unique distance values
+ * still being visible at init time.
+ */
+ if (!node_online(j))
+ continue;
+
if (sched_debug() && (node_distance(j, k) != node_distance(k, j)))
sched_numa_warn("Node-distance not symmetric");

@@ -1886,6 +1898,53 @@ void sched_init_numa(void)
sched_max_numa_distance = sched_domains_numa_distance[nr_levels - 1];

init_numa_topology_type();
+
+ sched_numa_onlined_nodes = bitmap_alloc(nr_node_ids, GFP_KERNEL);
+ if (!sched_numa_onlined_nodes)
+ return;
+
+ bitmap_zero(sched_numa_onlined_nodes, nr_node_ids);
+ for_each_online_node(i)
+ bitmap_set(sched_numa_onlined_nodes, i, 1);
+}
+
+static void __sched_domains_numa_masks_set(unsigned int node)
+{
+ int i, j;
+
+ /*
+ * NUMA masks are not built for offline nodes in sched_init_numa().
+ * Thus, when a CPU of a never-onlined-before node gets plugged in,
+ * adding that new CPU to the right NUMA masks is not sufficient: the
+ * masks of that CPU's node must also be updated.
+ */
+ if (test_bit(node, sched_numa_onlined_nodes))
+ return;
+
+ bitmap_set(sched_numa_onlined_nodes, node, 1);
+
+ for (i = 0; i < sched_domains_numa_levels; i++) {
+ for (j = 0; j < nr_node_ids; j++) {
+ if (!node_online(j) || node == j)
+ continue;
+
+ if (node_distance(j, node) > sched_domains_numa_distance[i])
+ continue;
+
+ /* Add remote nodes in our masks */
+ cpumask_or(sched_domains_numa_masks[i][node],
+ sched_domains_numa_masks[i][node],
+ sched_domains_numa_masks[0][j]);
+ }
+ }
+
+ /*
+ * A new node has been brought up, potentially changing the topology
+ * classification.
+ *
+ * Note that this is racy vs any use of sched_numa_topology_type :/
+ */
+ init_numa_topology_type();
}

void sched_domains_numa_masks_set(unsigned int cpu)
@@ -1893,8 +1952,14 @@ void sched_domains_numa_masks_set(unsigned int cpu)
int node = cpu_to_node(cpu);
int i, j;

+ __sched_domains_numa_masks_set(node);
+
for (i = 0; i < sched_domains_numa_levels; i++) {
for (j = 0; j < nr_node_ids; j++) {
+ if (!node_online(j))
+ continue;
+
+ /* Set ourselves in the remote node's masks */
if (node_distance(j, node) <= sched_domains_numa_distance[i])
cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]);
}
--
2.30.2