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sched/topology: Switch to assigning "sd->shared" from s_data

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Use the "sched_domain_shared" object allocated in s_data for
"sd->shared" assignments. Assign "sd->shared" for the topmost
SD_SHARE_LLC domain before degeneration and rely on the degeneration
path to correctly pass down the shared object to "sd_llc".

sd_degenerate_parent() ensures degenerating domains must have the same
sched_domain_span() which ensures 1:1 passing down of the shared object.
If the topmost SD_SHARE_LLC domain degenerates, the shared object is
freed from destroy_sched_domain() when the last reference is dropped.

claim_allocations() NULLs out the objects that have been assigned as
"sd->shared" and the unassigned ones are freed from the __sds_free()
path.

To keep all the claim_allocations() bits in one place,
claim_allocations() has been extended to accept "s_data" and iterate the
domains internally to free both "sched_domain_shared" and the
per-topology-level data for the particular CPU in one place.

Post cpu_attach_domain(), all reclaims of "sd->shared" are handled via
call_rcu() on the sched_domain object via destroy_sched_domains_rcu().

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://patch.msgid.link/20260312044434.1974-5-kprateek.nayak@amd.com
This commit is contained in:
K Prateek Nayak 2026-03-12 04:44:29 +00:00 committed by Peter Zijlstra
parent 1cc8a33ca7
commit bb7a5e44fc
1 changed files with 44 additions and 29 deletions
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73
kernel/sched/topology.c
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@ -685,6 +685,9 @@ static void update_top_cache_domain(int cpu)
if (sd) {
id = cpumask_first(sched_domain_span(sd));
size = cpumask_weight(sched_domain_span(sd));
/* If sd_llc exists, sd_llc_shared should exist too. */
WARN_ON_ONCE(!sd->shared);
sds = sd->shared;
}
@ -733,6 +736,13 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
if (sd_parent_degenerate(tmp, parent)) {
tmp->parent = parent->parent;
/* Pick reference to parent->shared. */
if (parent->shared) {
WARN_ON_ONCE(tmp->shared);
tmp->shared = parent->shared;
parent->shared = NULL;
}
if (parent->parent) {
parent->parent->child = tmp;
parent->parent->groups->flags = tmp->flags;
@ -1586,21 +1596,28 @@ __visit_domain_allocation_hell(struct s_data *d, const struct cpumask *cpu_map)
* sched_group structure so that the subsequent __free_domain_allocs()
* will not free the data we're using.
*/
static void claim_allocations(int cpu, struct sched_domain *sd)
static void claim_allocations(int cpu, struct s_data *d)
{
struct sd_data *sdd = sd->private;
struct sched_domain *sd;
WARN_ON_ONCE(*per_cpu_ptr(sdd->sd, cpu) != sd);
*per_cpu_ptr(sdd->sd, cpu) = NULL;
if (atomic_read(&(*per_cpu_ptr(d->sds, cpu))->ref))
*per_cpu_ptr(d->sds, cpu) = NULL;
if (atomic_read(&(*per_cpu_ptr(sdd->sds, cpu))->ref))
*per_cpu_ptr(sdd->sds, cpu) = NULL;
for (sd = *per_cpu_ptr(d->sd, cpu); sd; sd = sd->parent) {
struct sd_data *sdd = sd->private;
if (atomic_read(&(*per_cpu_ptr(sdd->sg, cpu))->ref))
*per_cpu_ptr(sdd->sg, cpu) = NULL;
WARN_ON_ONCE(*per_cpu_ptr(sdd->sd, cpu) != sd);
*per_cpu_ptr(sdd->sd, cpu) = NULL;
if (atomic_read(&(*per_cpu_ptr(sdd->sgc, cpu))->ref))
*per_cpu_ptr(sdd->sgc, cpu) = NULL;
if (atomic_read(&(*per_cpu_ptr(sdd->sds, cpu))->ref))
*per_cpu_ptr(sdd->sds, cpu) = NULL;
if (atomic_read(&(*per_cpu_ptr(sdd->sg, cpu))->ref))
*per_cpu_ptr(sdd->sg, cpu) = NULL;
if (atomic_read(&(*per_cpu_ptr(sdd->sgc, cpu))->ref))
*per_cpu_ptr(sdd->sgc, cpu) = NULL;
}
}
#ifdef CONFIG_NUMA
@ -1738,16 +1755,6 @@ sd_init(struct sched_domain_topology_level *tl,
sd->cache_nice_tries = 1;
}
/*
* For all levels sharing cache; connect a sched_domain_shared
* instance.
*/
if (sd->flags & SD_SHARE_LLC) {
sd->shared = *per_cpu_ptr(sdd->sds, sd_id);
atomic_inc(&sd->shared->ref);
atomic_set(&sd->shared->nr_busy_cpus, sd_weight);
}
sd->private = sdd;
return sd;
@ -2729,12 +2736,20 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
while (sd->parent && (sd->parent->flags & SD_SHARE_LLC))
sd = sd->parent;
/*
* In presence of higher domains, adjust the
* NUMA imbalance stats for the hierarchy.
*/
if (IS_ENABLED(CONFIG_NUMA) && (sd->flags & SD_SHARE_LLC) && sd->parent)
adjust_numa_imbalance(sd);
if (sd->flags & SD_SHARE_LLC) {
int sd_id = cpumask_first(sched_domain_span(sd));
sd->shared = *per_cpu_ptr(d.sds, sd_id);
atomic_set(&sd->shared->nr_busy_cpus, sd->span_weight);
atomic_inc(&sd->shared->ref);
/*
* In presence of higher domains, adjust the
* NUMA imbalance stats for the hierarchy.
*/
if (IS_ENABLED(CONFIG_NUMA) && sd->parent)
adjust_numa_imbalance(sd);
}
}
/* Calculate CPU capacity for physical packages and nodes */
@ -2742,10 +2757,10 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
if (!cpumask_test_cpu(i, cpu_map))
continue;
for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
claim_allocations(i, sd);
claim_allocations(i, &d);
for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent)
init_sched_groups_capacity(i, sd);
}
}
/* Attach the domains */