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Tue, 7 Jul 2026 14:07:43 -0700 Date: Tue, 7 Jul 2026 14:07:42 -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> <20260707191329.GC226829@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260707191329.GC226829@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF000066E7:EE_|MW6PR12MB7070:EE_ X-MS-Office365-Filtering-Correlation-Id: af4042fd-7b8d-4c7c-d50e-08dedc6bd52c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|82310400026|36860700016|376014|7416014|1800799024|4143699003|56012099006|11063799006|18002099003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: B1OZjVB9/xJtaDUqqdHbw81qyUwwMvrDVrs07ujm0IZmtBNYSGd+6CMjRV5+ytVxf3d+LTGqaUEy3mHjQYuvsqmqwjUHkgk98s9joEZ+sl+frrh2K3S9T8Xt+Eu+q+FZT+NJy8f6pNHaSlc4u7+h7TrZJ0NR4drqkiJrsCNVnF0zDHQv1WBwcbETEhXQmIOCq6QsJOkIVOUxP/KFx20cSY7h8baO8J5OhRCdDHCimsuvdEnxGb+10cRuzDMN9bVf5ZttIlIDiKAmPsUf/0HWDgn7O5DSQd1b6kY6IMMxKfweCwFvFCVCjPdX8M0BSP6gToUMmUX2UpPyEBPR9ygry5fxB+kOCMcTzDGfiVHtbcIQl0Hf+x3QvvrLPI5bi3IG81dD0mDm58jjSpEqRhmqFNSm0cPzmTSfvTl0HhSI+jPcXaNPWgUxh5dTCo3j6zha X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jul 2026 21:08:02.8383 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: af4042fd-7b8d-4c7c-d50e-08dedc6bd52c X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.233];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000066E7.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW6PR12MB7070 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260707_140817_680199_B28E7625 X-CRM114-Status: GOOD ( 13.61 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jul 07, 2026 at 04:13:29PM -0300, Jason Gunthorpe wrote: > On Tue, Jul 07, 2026 at 12:27:00AM -0700, Nicolin Chen wrote: > > 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"? > > Oh, I guess it is at most 6 since it is +1 Yea, that's what I thought. log2(NUM + 1) could be 5, 4, 3, 2, 1, or 0. So, totally 6. > How about: > > /* > * The spec defines the invalidated range as: > * Range = ((NUM+1) * 2^SCALE) * Translation_Granule_Size > * NUM is 5 bits, so (NUM+1) covers 1..32 granules and SCALE scales > * that by a power of two. We must pick NUM and SCALE so the range > * covers num_tg granules, i.e. (NUM+1) * 2^SCALE >= num_tg with > * NUM+1 <= 32. That constrains SCALE to: > * ceil(num_tg / 2^SCALE) <= 32 > * SCALE >= ceil(log2(num_tg / 32)) > * Choosing the smallest such SCALE gives the finest granularity and > * thus the tightest (least over-covering) range, and equivalently the > * largest NUM. > * > * Unlike other IOMMUs the spec has no alignment requirement on the > * address beyond alignment to tg (so long as TTL=0). > */ This reads good to me. With that, Reviewed-by: Nicolin Chen