Re: [PATCH 39/49] arch/s390: replace cpumask_weight with cpumask_weight_eq where appropriate

[Sven Schnelle]

Hi Yury,

Yury Norov <yury.norov@xxxxxxxxx> writes:

> cfset_all_start() calls cpumask_weight() to compare the weight of cpumask
> with a given number. We can do it more efficiently with
> cpumask_weight_{eq, ...} because conditional cpumask_weight may stop
> traversing the cpumask earlier, as soon as condition is (or can't be) met.
>
> Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
> ---
>  arch/s390/kernel/perf_cpum_cf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
> index ee8707abdb6a..4d217f7f5ccf 100644
> --- a/arch/s390/kernel/perf_cpum_cf.c
> +++ b/arch/s390/kernel/perf_cpum_cf.c
> @@ -975,7 +975,7 @@ static int cfset_all_start(struct cfset_request *req)
>  		return -ENOMEM;
>  	cpumask_and(mask, &req->mask, cpu_online_mask);
>  	on_each_cpu_mask(mask, cfset_ioctl_on, &p, 1);
> -	if (atomic_read(&p.cpus_ack) != cpumask_weight(mask)) {
> +	if (!cpumask_weight_eq(mask, atomic_read(&p.cpus_ack))) {
>  		on_each_cpu_mask(mask, cfset_ioctl_off, &p, 1);
>  		rc = -EIO;
>  		debug_sprintf_event(cf_dbg, 4, "%s CPUs missing", __func__);

given that you're adding a bunch of these functions - gt,lt,eq and
others, i wonder whether it makes sense to also add cpumask_weight_ne(),
so one could just write:

if (cpumask_weight_ne(mask, atomic_read(&p.cpus_ack))) {
	...
}

?

/Sven