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From:   Sven Schnelle <svens@linux.ibm.com>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        David Laight <David.Laight@aculab.com>,
        Joe Perches <joe@perches.com>, Dennis Zhou <dennis@kernel.org>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Nicholas Piggin <npiggin@gmail.com>,
        Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
        Alexey Klimov <aklimov@redhat.com>,
        linux-kernel@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
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        Sumanth Korikkar <sumanthk@linux.ibm.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Jiapeng Chong <jiapeng.chong@linux.alibaba.com>,
        kernel test robot <lkp@intel.com>, linux-s390@vger.kernel.org
Subject: Re: [PATCH 39/49] arch/s390: replace cpumask_weight with
 cpumask_weight_eq where appropriate
References: <20220210224933.379149-1-yury.norov@gmail.com>
        <20220210224933.379149-40-yury.norov@gmail.com>
Date:   Fri, 11 Feb 2022 07:54:26 +0100
In-Reply-To: <20220210224933.379149-40-yury.norov@gmail.com> (Yury Norov's
        message of "Thu, 10 Feb 2022 14:49:23 -0800")
Message-ID: <yt9dwni17v19.fsf@linux.ibm.com>
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Hi Yury,

Yury Norov <yury.norov@gmail.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@gmail.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