Use cpumask_weighted_or() instead of cpumask_or() and cpumask_weight() on
the result, which walks the same bitmap twice. Results in 10-20% less
cycles, which reduces the runqueue lock hold time.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/sched/core.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10375,6 +10375,7 @@ void call_trace_sched_update_nr_running(
 static inline void mm_update_cpus_allowed(struct mm_struct *mm, const struct cpumask *affmsk)
 {
 	struct cpumask *mm_allowed;
+	unsigned int weight;
 
 	if (!mm)
 		return;
@@ -10385,8 +10386,8 @@ static inline void mm_update_cpus_allowe
 	 */
 	guard(raw_spinlock)(&mm->mm_cid.lock);
 	mm_allowed = mm_cpus_allowed(mm);
-	cpumask_or(mm_allowed, mm_allowed, affmsk);
-	WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, cpumask_weight(mm_allowed));
+	weight = cpumask_weighted_or(mm_allowed, mm_allowed, affmsk);
+	WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, weight);
 }
 
 void sched_mm_cid_exit_signals(struct task_struct *t)

On 2025-10-29 09:09, Thomas Gleixner wrote:
> Use cpumask_weighted_or() instead of cpumask_or() and cpumask_weight() on
> the result, which walks the same bitmap twice. Results in 10-20% less
> cycles, which reduces the runqueue lock hold time.
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com