linux-kernel - Re: [PATCH 1/4] cpumask: relax cpumask_any

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Message-ID: <2aa4169d-a26a-429b-9deb-dcf19baa763e@intel.com>
Date: Wed, 23 Apr 2025 14:28:03 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Yury Norov <yury.norov@...il.com>, Tony Luck <tony.luck@...el.com>,
	"Thomas Gleixner" <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	"Borislav Petkov" <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Rasmus Villemoes
	<linux@...musvillemoes.dk>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] cpumask: relax cpumask_any_but()

Hi Yury,

On 4/7/25 8:38 AM, Yury Norov wrote:
> From: Yury Norov [NVIDIA] <yury.norov@...il.com>
> 
> Similarly to other cpumask search functions, accept -1, and consider
> it as 'any cpu' hint. This helps users to avoid coding special cases.
> 
> Signed-off-by: Yury Norov [NVIDIA] <yury.norov@...il.com>
> ---
>  include/linux/cpumask.h | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index beff4d26e605..0f816092c891 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -413,6 +413,7 @@ unsigned int cpumask_next_wrap(int n, const struct cpumask *src)
>   * @cpu: the cpu to ignore.
>   *
>   * Often used to find any cpu but smp_processor_id() in a mask.
> + * If @cpu == -1, the function is equivalent to cpumask_any().

Now that -1 is a legal argument, should the "cpu" parameter be of "int" type (instead of
"unsigned int")?


>   * Return: >= nr_cpu_ids if no cpus set.
>   */
>  static __always_inline
> @@ -420,7 +421,10 @@ unsigned int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
>  {
>  	unsigned int i;
>  
> -	cpumask_check(cpu);
> +	/* -1 is a legal arg here. */
> +	if (cpu != -1)
> +		cpumask_check(cpu);
> +
>  	for_each_cpu(i, mask)
>  		if (i != cpu)
>  			break;
> @@ -433,6 +437,7 @@ unsigned int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
>   * @mask2: the second input cpumask
>   * @cpu: the cpu to ignore
>   *
> + * If @cpu == -1, the function is equivalent to cpumask_any_and().
>   * Returns >= nr_cpu_ids if no cpus set.
>   */
>  static __always_inline
> @@ -442,7 +447,10 @@ unsigned int cpumask_any_and_but(const struct cpumask *mask1,

Same question here regarding type of "cpu" parameter.

>  {
>  	unsigned int i;
>  
> -	cpumask_check(cpu);
> +	/* -1 is a legal arg here. */
> +	if (cpu != -1)
> +		cpumask_check(cpu);
> +
>  	i = cpumask_first_and(mask1, mask2);
>  	if (i != cpu)
>  		return i;

Reinette