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x86/mp: don't create empty cpu groups

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When some APICs are disabled by tunables, some cpu groups could end up
empty. An empty cpu group causes the system to panic because not all
functions handle them correctly. Additionally, it's wasted time to
handle and inspect empty cpu groups. Therefore, just don't create them.

Reviewed by:	kib, avg, cem
Sponsored by:	Beckhoff Automation GmbH & Co. KG
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D24927
This commit is contained in:
Corvin Köhne 2022-05-30 11:19:14 +02:00 committed by Emmanuel Vadot
parent 3ba952e1a2
commit 7468332f55
1 changed files with 28 additions and 2 deletions
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30
sys/x86/x86/mp_x86.c
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@ -871,6 +871,25 @@ x86topo_add_sched_group(struct topo_node *root, struct cpu_group *cg_root)
nchildren = 0;
node = root;
while (node != NULL) {
/*
* When some APICs are disabled by tunables, nodes can end up
* with an empty cpuset. Nodes with an empty cpuset will be
* translated into cpu groups with empty cpusets. smp_topo_fill
* will then set cg_first and cg_last to -1. This isn't
* correctly handled in all functions. E.g. when
* cpu_search_lowest and cpu_search_highest loop through all
* cpus, they call CPU_ISSET on cpu -1 which ends up in a
* general protection fault.
*
* We could fix the scheduler to handle empty cpu groups
* correctly. Nevertheless, empty cpu groups are causing
* overhead for no value. So, it makes more sense to just don't
* create them.
*/
if (CPU_EMPTY(&node->cpuset)) {
node = topo_next_node(root, node);
continue;
}
if (CPU_CMP(&node->cpuset, &root->cpuset) == 0) {
if (node->type == TOPO_TYPE_CACHE &&
cg_root->cg_level < node->subtype)
@ -896,8 +915,14 @@ x86topo_add_sched_group(struct topo_node *root, struct cpu_group *cg_root)
if (nchildren == root->cpu_count)
return;
cg_root->cg_child = smp_topo_alloc(nchildren);
/*
* We are not interested in nodes without children.
*/
cg_root->cg_children = nchildren;
if (nchildren == 0)
return;
cg_root->cg_child = smp_topo_alloc(nchildren);
/*
* Now find again the same cache nodes as above and recursively
@ -909,7 +934,8 @@ x86topo_add_sched_group(struct topo_node *root, struct cpu_group *cg_root)
if ((node->type != TOPO_TYPE_GROUP &&
node->type != TOPO_TYPE_NODE &&
node->type != TOPO_TYPE_CACHE) ||
CPU_CMP(&node->cpuset, &root->cpuset) == 0) {
CPU_CMP(&node->cpuset, &root->cpuset) == 0 ||
CPU_EMPTY(&node->cpuset)) {
node = topo_next_node(root, node);
continue;
}