From 67c9ab800f28628d0cdd99a90eca2924dd571944 Mon Sep 17 00:00:00 2001 From: Nicholas Mc Guire Date: Mon, 24 Mar 2014 13:18:48 +0100 Subject: sched: dont calculate hweight in update_migrate_disable() Proposal for a minor optimization in update_migrate_disable - its only a few instructions saved but those are in the hot path of locks so it might be worth it When being scheduled out while migrate_disable > 0 and migrate_disabled_updated is not yet set we end up here (kernel/sched/core.c): static inline void update_migrate_disable(struct task_struct *p) { ... mask = tsk_cpus_allowed(p); if (p->sched_class->set_cpus_allowed) p->sched_class->set_cpus_allowed(p, mask); p->nr_cpus_allowed = cpumask_weight(mask); as we only can get here if migrate_disable > 0 there is no need to calculate the cpumask_weight(mask) as tsk_cpus_allowed in that case will return cpumask_of(task_cpu(p)) which only can have a hamming weight of 1 anyway. So we can simply do: p->nr_cpus_allowed = 1; without changing the behavior. Reviewed-by: Steven Rostedt Signed-off-by: Nicholas Mc Guire Signed-off-by: Sebastian Andrzej Siewior diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1105e72..e98f555 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2394,7 +2394,8 @@ static inline void update_migrate_disable(struct task_struct *p) if (p->sched_class->set_cpus_allowed) p->sched_class->set_cpus_allowed(p, mask); - p->nr_cpus_allowed = cpumask_weight(mask); + /* mask==cpumask_of(task_cpu(p)) which has a cpumask_weight==1 */ + p->nr_cpus_allowed = 1; /* Let migrate_enable know to fix things back up */ p->migrate_disable |= MIGRATE_DISABLE_SET_AFFIN; -- cgit v0.10.2