Subject: Re: [PATCH 08/16] smp: optimize smp_call_function_many_cond() for more

From: Peter Zijlstra <[email-masked]>
Date: Mon, 18 Jul 2022 23:29:06 +0200

On Mon, Jul 18, 2022 at 12:28:36PM -0700, Yury Norov wrote:

> ---
>  kernel/smp.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 7ed2b9b12f74..f96fdf944b4a 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -942,7 +942,11 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
>  
>  	if (run_remote) {
>  		cfd = this_cpu_ptr(&cfd_data);
> -		cpumask_and(cfd->cpumask, mask, cpu_online_mask);
> +		if (mask == cpu_online_mask)
> +			cpumask_copy(cfd->cpumask, cpu_online_mask);
> +		else
> +			cpumask_and(cfd->cpumask, mask, cpu_online_mask);
> +

Or... you could optimize cpumask_and() to detect the src1p == src2p case?

>  		__cpumask_clear_cpu(this_cpu, cfd->cpumask);
>  
>  		cpumask_clear(cfd->cpumask_ipi);
> -- 
> 2.34.1
>