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charset=UTF-8 Date: Mon, 17 Aug 2026 16:03:51 +0900 Message-Id: Cc: "Danilo Krummrich" , "Alice Ryhl" , "Burak Emir" , "Yury Norov" , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , "Daniel Almeida" , "Tamir Duberstein" , "Alexandre Courbot" , =?utf-8?q?Onur_=C3=96zkan?= , "David Airlie" , "Simona Vetter" , "Greg Kroah-Hartman" , "John Hubbard" , "Alistair Popple" , "Timur Tabi" , "Zhi Wang" , , , , , "dri-devel" Subject: Re: [PATCH v5 5/5] gpu: nova-core: add ChannelIdPool From: "Eliot Courtney" To: "Yury Norov" , "Eliot Courtney" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260812-chid-v5-0-6c767770b3f4@nvidia.com> <20260812-chid-v5-5-6c767770b3f4@nvidia.com> In-Reply-To: X-ClientProxiedBy: DUZPR01CA0227.eurprd01.prod.exchangelabs.com (2603:10a6:10:4b4::15) To BL0PR12MB2353.namprd12.prod.outlook.com (2603:10b6:207:4c::31) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL0PR12MB2353:EE_|MW4PR12MB6732:EE_ X-MS-Office365-Filtering-Correlation-Id: bad77bc2-192c-46e1-7e33-08defc2db59a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|7416014|1800799024|366016|10070799003|376014|10067099003|4143699003|11063799006|56012099006|18002099003|22082099003|3023799007; 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Provide a nz! macro to create constant non-zero things. Provide s= ome >> > > constants for common alignments >> > > >> > > Potentially, we could use build_assert! for cases it is provably >> > > non-zero but not a literal (although tbh not sure this is a good ide= a - >> > > at least not do this initially).=20 >> > > >> > > So either: nz!: const { NonZero::new(value).unwrap() }, or, nz!: som= e >> > > build assert gated construction of NonZero. A general nz! macro coul= d >> > > also help ergonomics for other use cases too. >> > > >> > > That looks like this: >> > > >> > > pool.alloc_area(nz!(8), Alignment::AL_8)?; >> >=20 >> > Actually found that if we implement SizeConstants for Alignment then w= e >> > can get Alignment::SZ_4K etc almost for free. >>=20 >> Then maybe pass SZ_4K directly, and allow the alloc_area() to >> calculate the alignment: >>=20 >> pool.alloc_area(nz!(8), SZ_4K)?; > > Even worse, you can advertise the function like: allocate a contiguous > set of channel IDs enough to represent XXX bytes of memory with YYY > alignment. And that way, you'll be able to do: > > pool.alloc_area(SZ_8K, SZ_4K)?; > > If my understanding of the function is right, it would be a clear > improvement, because the user now doesn't think about ID channels pool > as a set of bits, but an abstraction over the memory access technique, > which it really is. If we pass SZ_4K directly, we are back to using plain integers, which is not what we should be doing for rust interfaces according to Miguel. Let me send a new version of this with my Alignment constants + nz! macro idea, IMO it helps with the verbosity. I don't quite understand your point about memory access. The purpose here is just to be an allocator of IDs, not memory - it's just that we have some contiguousness and alignment requirements of the IDs themselves. The values we're passing in just represent numbers of channels and constraints on those. I think that callers will naturally want to allocate a particular number of channels, not a specific amount of memory that corresponds to some number of channels in some way (e.g. USERD?). On pre-Blackwell, OpenRM makes channel ID area reservations for vGPU power of two number of channels and and places them so the base channel ID is aligned to the number of channels. Sorry if I have misunderstood your point. Maybe we should rename `alloc_area` to `reserve_ids` or something like that if it would make it clearer?