powerpc/smp: Optimize remove_cpu_from_masks

While offlining a CPU, system currently iterate through all the CPUs in
the DIE to clear sibling, l2_cache and smallcore maps. However if there
are more cores in a DIE, system can end up spending more time iterating
through CPUs which are completely unrelated.

Optimize this by only iterating through smaller but relevant cpumap.
If shared_cache is set, cpu_l2_cache_map should be relevant else
cpu_sibling_map would be relevant.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200921095653.9701-5-srikar@linux.vnet.ibm.com

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index aecc01f0e95e4db09100ea095c401bbf56f0e1d8..9cdb966f00b39d9af580b3ef4d2780ee024cb369 100644 (file)
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1263,14 +1263,21 @@ static bool update_mask_by_l2(int cpu, struct cpumask *(*mask_fn)(int))
 #ifdef CONFIG_HOTPLUG_CPU
 static void remove_cpu_from_masks(int cpu)
 {
+       struct cpumask *(*mask_fn)(int) = cpu_sibling_mask;
        int i;
 
-       for_each_cpu(i, cpu_cpu_mask(cpu)) {
+       if (shared_caches)
+               mask_fn = cpu_l2_cache_mask;
+
+       for_each_cpu(i, mask_fn(cpu)) {
                set_cpus_unrelated(cpu, i, cpu_l2_cache_mask);
                set_cpus_unrelated(cpu, i, cpu_sibling_mask);
                if (has_big_cores)
                        set_cpus_unrelated(cpu, i, cpu_smallcore_mask);
-               if (has_coregroup_support())
+       }
+
+       if (has_coregroup_support()) {
+               for_each_cpu(i, cpu_coregroup_mask(cpu))
                        set_cpus_unrelated(cpu, i, cpu_coregroup_mask);
        }
 }