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Sun, 18 May 2025 08:19:36 -0700 Date: Sun, 18 May 2025 08:19:34 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "corbet@lwn.net" , "will@kernel.org" , "bagasdotme@gmail.com" , "robin.murphy@arm.com" , "joro@8bytes.org" , "thierry.reding@gmail.com" , "vdumpa@nvidia.com" , "jonathanh@nvidia.com" , "shuah@kernel.org" , "jsnitsel@redhat.com" , "nathan@kernel.org" , "peterz@infradead.org" , "Liu, Yi L" , "mshavit@google.com" , "praan@google.com" , "zhangzekun11@huawei.com" , "iommu@lists.linux.dev" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "patches@lists.linux.dev" , "mochs@nvidia.com" , "alok.a.tiwari@oracle.com" , "vasant.hegde@amd.com" Subject: Re: [PATCH v4 11/23] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC ioctl Message-ID: References: Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 May 2025 15:19:46.7276 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8b4b9fb6-155f-4436-fe52-08dd961f6cbb X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000A345.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR12MB9272 Hi Kevin, On Thu, May 15, 2025 at 09:05:11PM -0700, Nicolin Chen wrote: > On Fri, May 16, 2025 at 03:52:16AM +0000, Tian, Kevin wrote: > > But hey, we are already adding various restrictions to the uAPI > > about dependency, contiguity, etc. which the VMM should conform > > to. What hurts if we further say that the VMM should allocate > > virtual index in an ascending order along with hw queue allocation? > > You mean adding another flag to manage the dependency in the core, > right? > > I talked with Jason offline when adding that depend API. He didn't > want it to be in the core, saying that is a driver thing. > > But that was before we added pin and contiguity, which he doesn't > really enjoy being in the core either. > > So, yea, I think you have a point here.. It seems Jason is out of office. And in the last sync w.r.t this, he thinks that this ascending order stuff is too unique/weird to make sense as a feature in the core, that there would be unlikely a second HW wanting this.. I think that's a valid point too. The pin/contiguity requirement at least serves for HW that reads in physical address space, and it could result in a slightly faster memory access since it does not need a translation, which though gives software some trouble yet still makes sense IMHO. So, in v5, I kept the dependency APIs rather than moving to the core. I think we can move to the core later if we see another HW doing the same thing. Thanks Nicolin