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Date: Mon, 2 Feb 2026 17:05:00 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Julien Grall , Stefano Stabellini , Anthony PERARD , Michal Orzel Subject: Re: [PATCH] CPU: abstract read-mostly-ness for per-CPU cpumask_var_t variables Message-ID: References: <7eed3c7e-b3e8-4a0c-bd6d-c4ba22bb1c10@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7eed3c7e-b3e8-4a0c-bd6d-c4ba22bb1c10@suse.com> X-ClientProxiedBy: MR1P264CA0118.FRAP264.PROD.OUTLOOK.COM (2603:10a6:501:50::25) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|BN8PR03MB5044:EE_ X-MS-Office365-Filtering-Correlation-Id: 5ba6175e-b263-4474-6377-08de6274d3ab X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016|7053199007; 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While the pointer > >> typically is allocated once for a CPU and then only read (i.e. wants to be > >> marked read-mostly), the same isn't necessarily true for the array case. > >> There things depend on how the variable is actually used. cpu_core_mask > >> and cpu_sibling_mask (which all architectures have inherited from x86, > >> which in turn is possibly wrong) are altered only as CPUs are brought up > >> or down, so may remain uniformly read-mostly. Other (x86-only) instances > >> want to change, to avoid disturbing adjacent read-mostly data. > >> > >> While doing the x86 adjustment, also do one in the opposite direction, > >> i.e. where there was no read-mostly annotation when it is applicable in > >> the "pointer" case. > >> > >> Signed-off-by: Jan Beulich > > > > Acked-by: Roger Pau Monné > > Thanks. > > >> --- > >> Really in the pointer case it would be nice if the allocations could then > >> also come from "read-mostly" space. > > > > Hm, I guess for some of them yes, it would make sense to come from > > __read_mostly space, but would require passing an extra parameter to > > the DEFINE_ helper? Or introduce another variant. > > Whether this could be sorted purely at the macro wrapper layer I'm not > sure. It's the actual allocation (which alloc_cpumask_var() et al do) > which would need to be more sophisticated than a simple _x[mz]alloc(). For the array case it could be sorted out in the macro wrapper - for the pointer case it would need to be sorted at allocation, which makes this quite weird to deal with. Anyway, this is better than nothing I guess. Thanks, Roger.