linux-kernel - Re: [PATCH v2 2/7] sparc/irq: Remove on-stack cpumask var

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Message-ID: <20240420082239.GB614130@ravnborg.org>
Date: Sat, 20 Apr 2024 10:22:39 +0200
From: Sam Ravnborg <sam@...nborg.org>
To: Dawei Li <dawei.li@...ngroup.cn>
Cc: davem@...emloft.net, andreas@...sler.com, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] sparc/irq: Remove on-stack cpumask var

On Sat, Apr 20, 2024 at 01:15:42PM +0800, Dawei Li wrote:
> In general it's preferable to avoid placing cpumasks on the stack, as
> for large values of NR_CPUS these can consume significant amounts of
> stack space and make stack overflows more likely.
> 
> - Both 2 arguments of cpumask_equal() is constant and free of change, no
>   need to allocate extra cpumask variables.
> 
> - Merge cpumask_and(), cpumask_first() and cpumask_empty() into
>   cpumask_first_and().
> 
> Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>
Reviewed-by: Sam Ravnborg <sam@...nborg.org>
> ---
>  arch/sparc/kernel/irq_64.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
> index 5280e325d4d6..01ee800efde3 100644
> --- a/arch/sparc/kernel/irq_64.c
> +++ b/arch/sparc/kernel/irq_64.c
> @@ -349,17 +349,13 @@ static unsigned int sun4u_compute_tid(unsigned long imap, unsigned long cpuid)
>  #ifdef CONFIG_SMP
>  static int irq_choose_cpu(unsigned int irq, const struct cpumask *affinity)
>  {
> -	cpumask_t mask;
>  	int cpuid;
>  
> -	cpumask_copy(&mask, affinity);
> -	if (cpumask_equal(&mask, cpu_online_mask)) {
> +	if (cpumask_equal(affinity, cpu_online_mask)) {
>  		cpuid = map_to_cpu(irq);
>  	} else {
> -		cpumask_t tmp;
> -
> -		cpumask_and(&tmp, cpu_online_mask, &mask);
> -		cpuid = cpumask_empty(&tmp) ? map_to_cpu(irq) : cpumask_first(&tmp);
> +		cpuid = cpumask_first_and(affinity, cpu_online_mask);
> +		cpuid = cpuid < nr_cpu_ids ? cpuid : map_to_cpu(irq);
>  	}
>  
>  	return cpuid;
> -- 
> 2.27.0