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Mon, 24 Aug 2026 15:15:30 +0000 Message-ID: <1a78d1e2-f3b2-487b-9bd8-8d22ee680b01@intel.com> Date: Mon, 24 Aug 2026 23:15:19 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/9] x86/resctrl: Require 64-bit x86 for resctrl support To: Dave Hansen , Chen Yu , "Reinette Chatre" CC: Borislav Petkov , "Luck, Tony" , "tglx@kernel.org" , "mingo@redhat.com" , "dave.hansen@linux.intel.com" , "hpa@zytor.com" , "fenghuay@nvidia.com" , "babu.moger@amd.com" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" References: <980c4d9c15862de0b0dbc535b646f6b96ea46abe.1784968626.git.yu.c.chen@intel.com> <6c933b5c-620d-4684-b651-48a7ebdfc956@intel.com> <7911abea-d508-4401-b6de-2f6f598f08bf@intel.com> <20260821023700.GAaoe5zEH173SJwxga@fat_crate.local> <03e10b76-01d7-47cf-b139-a29f41e0c47f@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI1PR02CA0009.apcprd02.prod.outlook.com (2603:1096:4:1f7::10) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|IA1PR11MB8200:EE_ X-MS-Office365-Filtering-Correlation-Id: 216bb179-c240-4745-0b14-08df01f2892c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|366016|1800799024|376014|7416014|10067099003|56012099006|22082099003|18002099003|4143699003|5023799004|11063799006; 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New CPU features are generally >> not enabled for 32-bit system, its test coverage keeps shrinking, and modern >> 32-bit distributions have become rare." > > What would folks think about plopping something like the following text > in to Documentation/arch/x86/32bit-kernels.rst ? > > Would that clear things up? > Thanks, Dave, for the detailed document. It will be very helpful. > --- > > ========================================= > Supporting new features on 32-bit kernels > ========================================= > > While it is possible to compile and run a 32-bit kernel on 64-bit > capable hardware, it is impractical and discouraged. Processors > capable of running 64-bit kernels are expected to do so. > > The last 32-bit processor to come out of Intel or AMD was a Quark CPU > in 2013. Before that the most recent were some Atom CPUs in 2008. > > Distros supporting 32-bit kernels and userspace are disappearing. For > example, in 2026 Ubuntu and Fedora no longer have support, with Debian > being the most notable holdout still maintaining 32-bit options. According to https://www.debian.org/releases/trixie/release-notes/issues.en.html#i386-reduced-support "From trixie, i386 is no longer supported as a regular architecture" > > New Processor Features > ====================== > > When adding support for a new processor feature in 2026 and beyond it > should, by default, be: > > config NEW_SNAZZY_CPU_FEATURE > depends X86_64 depends on X86_64 thanks, Chenyu > > This ensures that the folks developing this feature do not waste > resources making it work on 32-bit kernels running on 64-bit hardware. > > It is also acceptable to add this restriction to existing processor > features if 32-bit kernel support is adding maintenance burden, > especially if the feature was only ever available on 64-bit processors. > > New Software Features > ===================== > > Let's say you are enhancing ftrace or adding a debugging feature that > has no strict dependency on processor features. It does not need to > be restricted to 64-bit only. But you might want to consider doing so > if it simplifies your implementation. > > For instance, sometimes it adds complexity to support HIGHMEM. You may > add a dependency on X86_64 in cases where it is impractical or simply > challenging to support 32-bit kernels.