linux-kernel - Re: [PATCH] ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512

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Message-ID: <ZaVRlHpAOoNIiRiY@shell.armlinux.org.uk>
Date: Mon, 15 Jan 2024 15:39:00 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: "Christoph Lameter (Ampere)" <cl@...ux.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Valentin.Schneider@....com,
	Vanshidhar Konda <vanshikonda@...amperecomputing.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Robin Murphy <robin.murphy@....com>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Matteo Carlini <Matteo.Carlini@....com>, akpm@...ux-foundation.org,
	yang@...amperecomputing.com
Subject: Re: [PATCH] ARM64: Dynamically allocate cpumasks and increase
 supported CPUs to 512

On Thu, Dec 14, 2023 at 04:05:56PM -0800, Christoph Lameter (Ampere) wrote:
> Index: linux/arch/arm64/Kconfig
> ===================================================================
> --- linux.orig/arch/arm64/Kconfig
> +++ linux/arch/arm64/Kconfig
> @@ -1407,7 +1407,21 @@ config SCHED_SMT
>   config NR_CPUS
>   	int "Maximum number of CPUs (2-4096)"
>   	range 2 4096

I think your mailer got to your patch and messed up the white space.
There are two spaces before each of these lines rather than the usual
one.

> -	default "256"
> +	default 512
> +
> +#
> +# Determines the placement of cpumasks.
> +#
> +# With CPUMASK_OFFSTACK the cpumasks are dynamically allocated.
> +# Useful for machines with lots of core because it avoids increasing
> +# the size of many of the data structures in the kernel.
> +#
> +# If this is off then the cpumasks have a static sizes and are
> +# embedded within data structures.
> +#
> +config CPUMASK_OFFSTACK
> +	def_bool y
> +	depends on NR_CPUS > 256

Should that be ">= 256" ?

> 
>   config HOTPLUG_CPU
>   	bool "Support for hot-pluggable CPUs"

Same here.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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