linux-kernel - Re: [PATCH 39/49] arch/s390: replace cpumask_weight with cpumask_weight

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Date:   Fri, 11 Feb 2022 07:54:26 +0100
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Joe Perches <joe@...ches.com>, Dennis Zhou <dennis@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Nicholas Piggin <npiggin@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Alexey Klimov <aklimov@...hat.com>,
        linux-kernel@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Sumanth Korikkar <sumanthk@...ux.ibm.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
        kernel test robot <lkp@...el.com>, linux-s390@...r.kernel.org
Subject: Re: [PATCH 39/49] arch/s390: replace cpumask_weight with
 cpumask_weight_eq where appropriate

Hi Yury,

Yury Norov <yury.norov@...il.com> 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@...il.com>
> ---
>  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