powerpc/numa: stub out numa_update_cpu_topology()

Previous changes have removed the code which sets bits in
cpu_associativity_changes_mask and thus it is never modifed at
runtime. From this we can reason that numa_update_cpu_topology()
always returns 0 without doing anything. Remove the body of
numa_update_cpu_topology() and remove all code which becomes
unreachable as a result.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200612051238.1007764-10-nathanl@linux.ibm.com

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 8749d7f2b1a63a6b2e4955508035d7a6944a6ece..b220e5b60140f13440e6cc1e76f9f5a0b7fab2e1 100644 (file)
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1122,14 +1122,6 @@ u64 memory_hotplug_max(void)
 
 /* Virtual Processor Home Node (VPHN) support */
 #ifdef CONFIG_PPC_SPLPAR
-struct topology_update_data {
-       struct topology_update_data *next;
-       unsigned int cpu;
-       int old_nid;
-       int new_nid;
-};
-
-static cpumask_t cpu_associativity_changes_mask;
 static int topology_inited;
 
 /*
@@ -1219,192 +1211,9 @@ int find_and_online_cpu_nid(int cpu)
        return new_nid;
 }
 
-/*
- * Update the CPU maps and sysfs entries for a single CPU when its NUMA
- * characteristics change. This function doesn't perform any locking and is
- * only safe to call from stop_machine().
- */
-static int update_cpu_topology(void *data)
-{
-       struct topology_update_data *update;
-       unsigned long cpu;
-
-       if (!data)
-               return -EINVAL;
-
-       cpu = smp_processor_id();
-
-       for (update = data; update; update = update->next) {
-               int new_nid = update->new_nid;
-               if (cpu != update->cpu)
-                       continue;
-
-               unmap_cpu_from_node(cpu);
-               map_cpu_to_node(cpu, new_nid);
-               set_cpu_numa_node(cpu, new_nid);
-               set_cpu_numa_mem(cpu, local_memory_node(new_nid));
-               vdso_getcpu_init();
-       }
-
-       return 0;
-}
-
-static int update_lookup_table(void *data)
-{
-       struct topology_update_data *update;
-
-       if (!data)
-               return -EINVAL;
-
-       /*
-        * Upon topology update, the numa-cpu lookup table needs to be updated
-        * for all threads in the core, including offline CPUs, to ensure that
-        * future hotplug operations respect the cpu-to-node associativity
-        * properly.
-        */
-       for (update = data; update; update = update->next) {
-               int nid, base, j;
-
-               nid = update->new_nid;
-               base = cpu_first_thread_sibling(update->cpu);
-
-               for (j = 0; j < threads_per_core; j++) {
-                       update_numa_cpu_lookup_table(base + j, nid);
-               }
-       }
-
-       return 0;
-}
-
-/*
- * Update the node maps and sysfs entries for each cpu whose home node
- * has changed. Returns 1 when the topology has changed, and 0 otherwise.
- *
- * cpus_locked says whether we already hold cpu_hotplug_lock.
- */
 int numa_update_cpu_topology(bool cpus_locked)
 {
-       unsigned int cpu, sibling, changed = 0;
-       struct topology_update_data *updates, *ud;
-       cpumask_t updated_cpus;
-       struct device *dev;
-       int weight, new_nid, i = 0;
-
-       if (topology_inited)
-               return 0;
-
-       weight = cpumask_weight(&cpu_associativity_changes_mask);
-       if (!weight)
-               return 0;
-
-       updates = kcalloc(weight, sizeof(*updates), GFP_KERNEL);
-       if (!updates)
-               return 0;
-
-       cpumask_clear(&updated_cpus);
-
-       for_each_cpu(cpu, &cpu_associativity_changes_mask) {
-               /*
-                * If siblings aren't flagged for changes, updates list
-                * will be too short. Skip on this update and set for next
-                * update.
-                */
-               if (!cpumask_subset(cpu_sibling_mask(cpu),
-                                       &cpu_associativity_changes_mask)) {
-                       pr_info("Sibling bits not set for associativity "
-                                       "change, cpu%d\n", cpu);
-                       cpumask_or(&cpu_associativity_changes_mask,
-                                       &cpu_associativity_changes_mask,
-                                       cpu_sibling_mask(cpu));
-                       cpu = cpu_last_thread_sibling(cpu);
-                       continue;
-               }
-
-               new_nid = find_and_online_cpu_nid(cpu);
-
-               if (new_nid == numa_cpu_lookup_table[cpu]) {
-                       cpumask_andnot(&cpu_associativity_changes_mask,
-                                       &cpu_associativity_changes_mask,
-                                       cpu_sibling_mask(cpu));
-                       dbg("Assoc chg gives same node %d for cpu%d\n",
-                                       new_nid, cpu);
-                       cpu = cpu_last_thread_sibling(cpu);
-                       continue;
-               }
-
-               for_each_cpu(sibling, cpu_sibling_mask(cpu)) {
-                       ud = &updates[i++];
-                       ud->next = &updates[i];
-                       ud->cpu = sibling;
-                       ud->new_nid = new_nid;
-                       ud->old_nid = numa_cpu_lookup_table[sibling];
-                       cpumask_set_cpu(sibling, &updated_cpus);
-               }
-               cpu = cpu_last_thread_sibling(cpu);
-       }
-
-       /*
-        * Prevent processing of 'updates' from overflowing array
-        * where last entry filled in a 'next' pointer.
-        */
-       if (i)
-               updates[i-1].next = NULL;
-
-       pr_debug("Topology update for the following CPUs:\n");
-       if (cpumask_weight(&updated_cpus)) {
-               for (ud = &updates[0]; ud; ud = ud->next) {
-                       pr_debug("cpu %d moving from node %d "
-                                         "to %d\n", ud->cpu,
-                                         ud->old_nid, ud->new_nid);
-               }
-       }
-
-       /*
-        * In cases where we have nothing to update (because the updates list
-        * is too short or because the new topology is same as the old one),
-        * skip invoking update_cpu_topology() via stop-machine(). This is
-        * necessary (and not just a fast-path optimization) since stop-machine
-        * can end up electing a random CPU to run update_cpu_topology(), and
-        * thus trick us into setting up incorrect cpu-node mappings (since
-        * 'updates' is kzalloc()'ed).
-        *
-        * And for the similar reason, we will skip all the following updating.
-        */
-       if (!cpumask_weight(&updated_cpus))
-               goto out;
-
-       if (cpus_locked)
-               stop_machine_cpuslocked(update_cpu_topology, &updates[0],
-                                       &updated_cpus);
-       else
-               stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
-
-       /*
-        * Update the numa-cpu lookup table with the new mappings, even for
-        * offline CPUs. It is best to perform this update from the stop-
-        * machine context.
-        */
-       if (cpus_locked)
-               stop_machine_cpuslocked(update_lookup_table, &updates[0],
-                                       cpumask_of(raw_smp_processor_id()));
-       else
-               stop_machine(update_lookup_table, &updates[0],
-                            cpumask_of(raw_smp_processor_id()));
-
-       for (ud = &updates[0]; ud; ud = ud->next) {
-               unregister_cpu_under_node(ud->cpu, ud->old_nid);
-               register_cpu_under_node(ud->cpu, ud->new_nid);
-
-               dev = get_cpu_device(ud->cpu);
-               if (dev)
-                       kobject_uevent(&dev->kobj, KOBJ_CHANGE);
-               cpumask_clear_cpu(ud->cpu, &cpu_associativity_changes_mask);
-               changed = 1;
-       }
-
-out:
-       kfree(updates);
-       return changed;
+       return 0;
 }
 
 int arch_update_cpu_topology(void)