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sched/topology: Skip updating masks for non-online nodes

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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
This commit is contained in:
Valentin Schneider 2021-08-18 13:13:33 +05:30 committed by Peter Zijlstra
parent 746f5ea9c4
commit 0083242c93
1 changed files with 65 additions and 0 deletions
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65
kernel/sched/topology.c
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@ -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]);
}