#ifdef CONFIG_SCHED_SMT
/*
- * The sched_smt_present static key needs to be evaluated on every
- * hotplug event because at boot time SMT might be disabled when
- * the number of booted CPUs is limited.
- *
- * If then later a sibling gets hotplugged, then the key would stay
- * off and SMT scheduling would never be functional.
+ * When going up, increment the number of cores with SMT present.
*/
- if (cpumask_weight(cpu_smt_mask(cpu)) > 1)
- static_branch_enable_cpuslocked(&sched_smt_present);
+ if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+ static_branch_inc_cpuslocked(&sched_smt_present);
#endif
set_cpu_active(cpu, true);
*/
synchronize_rcu();
+#ifdef CONFIG_SCHED_SMT
+ /*
+ * When going down, decrement the number of cores with SMT present.
+ */
+ if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+ static_branch_dec_cpuslocked(&sched_smt_present);
+#endif
+
if (!sched_smp_initialized)
return 0;
/*
* There's no userspace yet to cause hotplug operations; hence all the
* CPU masks are stable and all blatant races in the below code cannot
- * happen.
+ * happen. The hotplug lock is nevertheless taken to satisfy lockdep,
+ * but there won't be any contention on it.
*/
+ cpus_read_lock();
mutex_lock(&sched_domains_mutex);
sched_init_domains(cpu_active_mask);
mutex_unlock(&sched_domains_mutex);
+ cpus_read_unlock();
/* Move init over to a non-isolated CPU */
if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)