From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 87CA5C61D85 for ; Thu, 23 Nov 2023 19:33:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229586AbjKWTdI (ORCPT ); Thu, 23 Nov 2023 14:33:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45566 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229453AbjKWTdG (ORCPT ); Thu, 23 Nov 2023 14:33:06 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0A473D59 for ; Thu, 23 Nov 2023 11:33:13 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E872EC433CA; Thu, 23 Nov 2023 19:33:10 +0000 (UTC) Date: Thu, 23 Nov 2023 19:33:08 +0000 From: Catalin Marinas To: "Christoph Lameter (Ampere)" Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Anshuman.Khandual@arm.com, Valentin.Schneider@arm.com, Vanshidhar Konda , Jonathan Cameron , Robin Murphy , Dave Kleikamp , Matteo Carlini Subject: Re: [PATCH ARM64]: Introduce CONFIG_MAXSMP to allow up to 512 cpus Message-ID: References: <6a854175-5f89-c754-17b8-deda18447f1f@gentwo.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6a854175-5f89-c754-17b8-deda18447f1f@gentwo.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 20, 2023 at 05:04:35PM -0800, Christoph Lameter (Ampere) wrote: > Index: linux/arch/arm64/Kconfig > =================================================================== > --- linux.orig/arch/arm64/Kconfig > +++ linux/arch/arm64/Kconfig > @@ -1402,10 +1402,56 @@ config SCHED_SMT > MultiThreading at a cost of slightly increased overhead in some > places. If unsure say N here. > > + > +config MAXSMP > + bool "Compile kernel with support for the maximum number of SMP Processors" > + depends on SMP && DEBUG_KERNEL > + select CPUMASK_OFFSTACK > + help > + Enable maximum number of CPUS and NUMA Nodes for this architecture. > + If unsure, say N. > + > +# > +# The maximum number of CPUs supported: > +# > +# The main config value is NR_CPUS, which defaults to NR_CPUS_DEFAULT, > +# and which can be configured interactively in the > +# [NR_CPUS_RANGE_BEGIN ... NR_CPUS_RANGE_END] range. > +# > +# ( If MAXSMP is enabled we just use the highest possible value and disable > +# interactive configuration. ) > +# > + > +config NR_CPUS_RANGE_BEGIN > + int > + default NR_CPUS_RANGE_END if MAXSMP > + default 1 if !SMP > + default 2 We don't support !SMP on arm64. > + > +config NR_CPUS_RANGE_END > + int > + default 8192 if SMP && CPUMASK_OFFSTACK > + default 512 if SMP && !CPUMASK_OFFSTACK > + default 1 if !SMP > + > +config NR_CPUS_DEFAULT > + int > + default 512 if MAXSMP > + default 64 if SMP > + default 1 if !SMP > + > config NR_CPUS > - int "Maximum number of CPUs (2-4096)" > - range 2 4096 > - default "256" > + int "Set maximum number of CPUs" if SMP && !MAXSMP > + range NR_CPUS_RANGE_BEGIN NR_CPUS_RANGE_END > + default NR_CPUS_DEFAULT > + help > + This allows you to specify the maximum number of CPUs which this > + kernel will support. If CPUMASK_OFFSTACK is enabled, the maximum > + supported value is 8192, otherwise the maximum value is 512. The > + minimum value which makes sense is 2. > + > + This is purely to save memory: each supported CPU adds about 8KB > + to the kernel image. Is this all needed just to select CPUMASK_OFFSTACK if larger NR_CPUS? Would something like this do: diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7b071a00425d..697d5700bad1 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -119,6 +119,7 @@ config ARM64 select CLONE_BACKWARDS select COMMON_CLK select CPU_PM if (SUSPEND || CPU_IDLE) + select CPUMASK_OFFSTACK if NR_CPUS > 512 select CRC32 select DCACHE_WORD_ACCESS select DYNAMIC_FTRACE if FUNCTION_TRACER togehther with a larger NR_CPUS in defconfig? -- Catalin