linux-kernel - Re: [PATCH] arm64: allow NR_CPUS=1 for non-SMP and adjust default accordingly

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Message-ID: <aINB80UeE9pqKvrC@arm.com>
Date: Fri, 25 Jul 2025 09:36:03 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Suchit Karunakaran <suchitkarunakaran@...il.com>
Cc: will@...nel.org, linux-arm-kernel@...ts.infradead.org,
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: allow NR_CPUS=1 for non-SMP and adjust default
 accordingly

On Thu, Jul 24, 2025 at 10:26:39PM +0530, Suchit Karunakaran wrote:
> The arm64 Kconfig for NR_CPUS previously required a minimum of 2 CPUs.
> This patch changes the minimum allowed CPUs to 1, enabling single-core
> non-SMP configurations.

Do you have such single-core system?

>  config NR_CPUS
> -	int "Maximum number of CPUs (2-4096)"
> -	range 2 4096
> -	default "512"
> +	int "Maximum number of CPUs (1-4096)"
> +	range 1 4096
> +	default "1" if !SMP
> +	default "512" if SMP

It's been some time since we forced CONFIG_SMP always on for arm64.

-- 
Catalin