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

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Message-ID: <CAO9wTFjYnNAiGXqczPMgmCMno2Y-T5GCmgBgjGfDRbEcvsyNhg@mail.gmail.com>
Date: Fri, 25 Jul 2025 14:12:14 +0530
From: Suchit K <suchitkarunakaran@...il.com>
To: Catalin Marinas <catalin.marinas@....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 Fri, 25 Jul 2025 at 14:06, Catalin Marinas <catalin.marinas@....com> wrote:
>
> 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?

No, I don't have a single core system. I've just used single core VMs
using QEMU, etc, but I don't know if it's equivalent.

>
> >  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.
>

I'm sorry, I wasn't aware of it. Thanks for the clarification.