On Sun, Jan 23, 2022 at 10:38:53AM -0800, Yury Norov wrote:
> 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@xxxxxxxxx>
Good point! Queued and pushed, thank you!
Thanx, Paul
> ---
> kernel/rcu/tree_nocb.h | 4 ++--
> kernel/rcu/tree_plugin.h | 2 +-
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index eeafb546a7a0..f83c7b1d6110 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -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);
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index c5b45c2f68a1..0dc0c8d6717c 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1215,7 +1215,7 @@ 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);
> free_cpumask_var(cm);
> --
> 2.30.2
>
