Re: [patch V4 08/20] sched/mmcid: Use cpumask_weighted_or()

[Yury Norov]

On Sun, Nov 16, 2025 at 09:48:49PM +0100, 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.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

Acked-by: Yury Norov (NVIDIA) <yury.norov@xxxxxxxxx>

> ---
>  kernel/sched/core.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -10377,6 +10377,7 @@ 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;
> @@ -10387,8 +10388,8 @@ 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)