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Date:   Wed, 13 Dec 2023 08:59:42 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: Re: [PATCH v3 6/7] lib/group_cpus: drop unneeded cpumask_empty()
 call in __group_cpus_evenly()
Message-ID: <ZXkB/qozJo2Nm9iE@fedora>
References: <20231212042108.682072-1-yury.norov@gmail.com>
 <20231212042108.682072-7-yury.norov@gmail.com>
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On Mon, Dec 11, 2023 at 08:21:06PM -0800, Yury Norov wrote:
> The function is called twice. First time it's called with
> cpumask_present as a parameter, which can't be empty. Second time it's
> called with a mask created with cpumask_andnot(), which returns false if
> the result is an empty mask.
> 
> We can safely drop redundand cpumask_empty() call from the
> __group_cpus_evenly() and save few cycles.
> 
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> ---
>  lib/group_cpus.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/group_cpus.c b/lib/group_cpus.c
> index c7fcd04c87bf..664a56171a1b 100644
> --- a/lib/group_cpus.c
> +++ b/lib/group_cpus.c
> @@ -252,9 +252,6 @@ static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
>  	nodemask_t nodemsk = NODE_MASK_NONE;
>  	struct node_groups *node_groups;
>  
> -	if (cpumask_empty(cpu_mask))
> -		return 0;
> -
>  	nodes = get_nodes_in_cpumask(node_to_cpumask, cpu_mask, &nodemsk);
>  
>  	/*
> @@ -394,9 +391,14 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
>  		curgrp = 0;
>  	else
>  		curgrp = nr_present;
> -	cpumask_andnot(npresmsk, cpu_possible_mask, npresmsk);
> -	ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
> -				  npresmsk, nmsk, masks);
> +
> +	if (cpumask_andnot(npresmsk, cpu_possible_mask, npresmsk))
> +		/* If npresmsk is not empty */
> +		ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
> +					  npresmsk, nmsk, masks);
> +	else
> +		ret = 0;
> +
>  	if (ret >= 0)
>  		nr_others = ret;

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming