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Tue, 7 Jul 2026 00:27:02 -0700 Date: Tue, 7 Jul 2026 00:27:00 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , "Joerg Roedel (AMD)" , Jean-Philippe Brucker , , Robin Murphy , Will Deacon , David Matlack , "Pasha Tatashin" , , "Pranjal Shrivastava" , Samiullah Khawaja , Mostafa Saleh Subject: Re: [PATCH v2 3/8] iommu/arm-smmu-v3: Optimize range invalidation for latency Message-ID: References: <0-v2-43074a57a53a+fb95-smmu_tlbi_jgg@nvidia.com> <3-v2-43074a57a53a+fb95-smmu_tlbi_jgg@nvidia.com> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <3-v2-43074a57a53a+fb95-smmu_tlbi_jgg@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001F1:EE_|SA1PR12MB8120:EE_ X-MS-Office365-Filtering-Correlation-Id: 3cceb60d-e0fe-4b1b-1f69-08dedbf93093 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|1800799024|376014|7416014|23010399003|82310400026|22082099003|18002099003|4143699003|11063799006|56012099006; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: oRwdp5pkFQq3Mh+WtdgE3IuY6MgbpYfitKFoMhDDkfmsm6vcpjL/Cl2YdUW9qkzFhDH/PW2qXwys1C55oB+vdCjKtwO1XwRsy9aC+5CzncZ2BbGHRAQdoSQNXEKvn+kOZ/l6x48XysTogu1vq1DGfppqC+TTIKHctA9iz5YGvf18nR5t8ze+OlFf73gNy3KEuxwRdJrcjDVwP6xNvcYU/z4ftiPEkz19OgU0aWjDTUl6jyImrl6QOeuKcHPe5sZP/adqOlD0Ic0u2Hyruc6pEHkODA/XNL/Q8/w4SlUVYzXGZEKWtptakbfGIJoLExLVdyiMSzL4CcgI06yHaQIOrzo7GlEmB1vOtd2QcwaB3WdxdWyEQkL5s+qMtXuwJ6jyvbwUJWvYxIedr+RHITkbajOdPgtTBIGkdgoVxrH7BoRu/US+nAMve98B3uLj95Pc X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jul 2026 07:27:24.0194 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3cceb60d-e0fe-4b1b-1f69-08dedbf93093 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001F1.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB8120 On Mon, Jul 06, 2026 at 01:26:40PM -0300, Jason Gunthorpe wrote: > + /* > + * There are at most 5 possible values for NUM based on SCALE. The Mind elaborating the "at most 5 possible values for NUM"? > + * highest NUM is at the lowest SCALE where: > + * ceil(num_tg / 2^SCALE) <= 32 > + * scale >= ceil(log2(num_tg / 32)) > + * The lowest value is 1 where 2^SCALE covers the whole range. Pick the > + * highest since it trivially also gives the tightest range. The spec only mentions: Range = ((NUM+1) * 2^SCALE) * Translation_Granule_Size Since CMDQ_TLBI_RANGE_NUM_MAX + 1 is 32, so we can get: num_tg <= 32 * 2^SCALE .. and then get that "ceil(num_tg / 2^SCALE) <= 32". Maybe worth adding the first two steps to help readability? Nicolin