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Mon, 29 Sep 2025 16:13:56 +0000 Received: from PH7PR12MB5757.namprd12.prod.outlook.com ([fe80::f012:300c:6bf4:7632]) by PH7PR12MB5757.namprd12.prod.outlook.com ([fe80::f012:300c:6bf4:7632%2]) with mapi id 15.20.9160.014; Mon, 29 Sep 2025 16:13:56 +0000 Date: Mon, 29 Sep 2025 13:13:54 -0300 From: Jason Gunthorpe To: Thomas =?utf-8?Q?Hellstr=C3=B6m?= Cc: Christian =?utf-8?B?S8O2bmln?= , intel-xe@lists.freedesktop.org, Matthew Brost , Maarten Lankhorst , Kasireddy Vivek , Simona Vetter , dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org Subject: Re: [RFC PATCH v2 1/2] dma-buf: Add support for private interconnects Message-ID: <20250929161354.GA2942991@nvidia.com> References: <20250926084624.2288-1-thomas.hellstrom@linux.intel.com> <20250926084624.2288-2-thomas.hellstrom@linux.intel.com> <472f27f0-2f54-45dd-b0a6-3a26b5eec301@amd.com> <20250926144128.GD2617119@nvidia.com> <765e3449-2eb1-49f5-954e-3bab5a5fc9d1@amd.com> <20250926160036.GE2617119@nvidia.com> <20250929124535.GI2617119@nvidia.com> <071c1bedd6fd902da9725c74c1b892c9fe76179c.camel@linux.intel.com> Content-Type: text/plain; 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TBH I think that at > least all fast interconnects we have in the planning for xe either are > fine with falling back to the current pcie-p2p / dma-buf or in worst > case system memory. Yah, fallback is fine, but they will still want to prefer the better paths if they are available. That's my point.. > The virtual interconnect we've been discussing > would probably not be able to fall back at all unless negotiation gets > somehow forwarded to the vm guest. This is basically proposing to open code all the priority and QOR matching in the drivers. I strongly think that will become unmaintainable if things evolve in that direction.. What I'm suggesting is to have just enough infrastructure that we can have the priority selection be in common code and implement the simplest possible selection for right now. Run down the exports list in order and the firt interconnect to match the importer's list is selected. All the more fancy stuff I've mentioned is someone else's problem down the road to enhance the core matcher. Jason