Commit 6a2c1d45 authored Jan 23, 2022 by Yury Norov Committed by Paul E. McKenney Feb 14, 2022

rcu: Replace cpumask_weight with cpumask_empty where appropriate

In some places, RCU code calls cpumask_weight() to check if any bit of a
given cpumask is set. We can do it more efficiently with cpumask_empty()
because cpumask_empty() stops traversing the cpumask as soon as it finds
first set bit, while cpumask_weight() counts all bits unconditionally.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent e6339d3b

kernel/rcu/tree_nocb.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -1169,7 +1169,7 @@ void __init rcu_init_nohz(void)
		struct rcu_data *rdp;

		#if defined(CONFIG_NO_HZ_FULL)
		if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
		if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
		need_rcu_nocb_mask = true;
		#endif /* #if defined(CONFIG_NO_HZ_FULL) */

		@@ -1348,7 +1348,7 @@ static void __init rcu_organize_nocb_kthreads(void)
		*/
		void rcu_bind_current_to_nocb(void)
		{
		if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
		if (cpumask_available(rcu_nocb_mask) && !cpumask_empty(rcu_nocb_mask))
		WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
		}
		EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);

kernel/rcu/tree_plugin.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -1220,7 +1220,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
		cpu != outgoingcpu)
		cpumask_set_cpu(cpu, cm);
		cpumask_and(cm, cm, housekeeping_cpumask(HK_FLAG_RCU));
		if (cpumask_weight(cm) == 0)
		if (cpumask_empty(cm))
		cpumask_copy(cm, housekeeping_cpumask(HK_FLAG_RCU));
		set_cpus_allowed_ptr(t, cm);
		mutex_unlock(&rnp->boost_kthread_mutex);