sched/topology: Allocate per-CPU sched_domain_shared in s_data

The "sched_domain_shared" object is allocated for every topology level
in __sdt_alloc() and is freed post sched domain rebuild if they aren't
assigned during sd_init().

"sd->shared" is only assigned for SD_SHARE_LLC domains and out of all
the assigned objects, only "sd_llc_shared" is ever used by the
scheduler.

Since only "sd_llc_shared" is ever used, and since SD_SHARE_LLC domains
never overlap, allocate only a single range of per-CPU
"sched_domain_shared" object with s_data instead of doing it per
topology level.

The subsequent commit uses the degeneration path to correctly assign the
"sd->shared" to the topmost SD_SHARE_LLC domain.

No functional changes are expected at this point.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://patch.msgid.link/20260312044434.1974-4-kprateek.nayak@amd.com

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6303790a414370d75e894d82930cfd43b8f46906..9006586720bf05a2f0b5864698811aaeb40b4148 100644 (file)
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -782,6 +782,7 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 }
 
 struct s_data {
+       struct sched_domain_shared * __percpu *sds;
        struct sched_domain * __percpu *sd;
        struct root_domain      *rd;
 };
@@ -789,6 +790,7 @@ struct s_data {
 enum s_alloc {
        sa_rootdomain,
        sa_sd,
+       sa_sd_shared,
        sa_sd_storage,
        sa_none,
 };
@@ -1535,6 +1537,9 @@ static void set_domain_attribute(struct sched_domain *sd,
 static void __sdt_free(const struct cpumask *cpu_map);
 static int __sdt_alloc(const struct cpumask *cpu_map);
 
+static void __sds_free(struct s_data *d, const struct cpumask *cpu_map);
+static int __sds_alloc(struct s_data *d, const struct cpumask *cpu_map);
+
 static void __free_domain_allocs(struct s_data *d, enum s_alloc what,
                                 const struct cpumask *cpu_map)
 {
@@ -1546,6 +1551,9 @@ static void __free_domain_allocs(struct s_data *d, enum s_alloc what,
        case sa_sd:
                free_percpu(d->sd);
                fallthrough;
+       case sa_sd_shared:
+               __sds_free(d, cpu_map);
+               fallthrough;
        case sa_sd_storage:
                __sdt_free(cpu_map);
                fallthrough;
@@ -1561,9 +1569,11 @@ __visit_domain_allocation_hell(struct s_data *d, const struct cpumask *cpu_map)
 
        if (__sdt_alloc(cpu_map))
                return sa_sd_storage;
+       if (__sds_alloc(d, cpu_map))
+               return sa_sd_shared;
        d->sd = alloc_percpu(struct sched_domain *);
        if (!d->sd)
-               return sa_sd_storage;
+               return sa_sd_shared;
        d->rd = alloc_rootdomain();
        if (!d->rd)
                return sa_sd;
@@ -2464,6 +2474,42 @@ static void __sdt_free(const struct cpumask *cpu_map)
        }
 }
 
+static int __sds_alloc(struct s_data *d, const struct cpumask *cpu_map)
+{
+       int j;
+
+       d->sds = alloc_percpu(struct sched_domain_shared *);
+       if (!d->sds)
+               return -ENOMEM;
+
+       for_each_cpu(j, cpu_map) {
+               struct sched_domain_shared *sds;
+
+               sds = kzalloc_node(sizeof(struct sched_domain_shared),
+                               GFP_KERNEL, cpu_to_node(j));
+               if (!sds)
+                       return -ENOMEM;
+
+               *per_cpu_ptr(d->sds, j) = sds;
+       }
+
+       return 0;
+}
+
+static void __sds_free(struct s_data *d, const struct cpumask *cpu_map)
+{
+       int j;
+
+       if (!d->sds)
+               return;
+
+       for_each_cpu(j, cpu_map)
+               kfree(*per_cpu_ptr(d->sds, j));
+
+       free_percpu(d->sds);
+       d->sds = NULL;
+}
+
 static struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl,
                const struct cpumask *cpu_map, struct sched_domain_attr *attr,
                struct sched_domain *child, int cpu)