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charset=UTF-8 Date: Fri, 21 Mar 2025 12:09:59 +0900 Message-Id: Cc: "Danilo Krummrich" , "David Airlie" , "John Hubbard" , "Ben Skeggs" , "Miguel Ojeda" , "Alex Gaynor" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Simona Vetter" , , , , Subject: Re: [PATCH RFC v3 6/7] gpu: nova-core: add basic timer device From: "Alexandre Courbot" To: "Daniel Brooks" X-Mailer: aerc 0.20.1-0-g2ecb8770224a References: <20250320-nova_timer-v3-0-79aa2ad25a79@nvidia.com> <20250320-nova_timer-v3-6-79aa2ad25a79@nvidia.com> <87v7s3zoha.fsf@db48x.net> In-Reply-To: <87v7s3zoha.fsf@db48x.net> X-ClientProxiedBy: TYWP286CA0024.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:262::9) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) 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: CH2PR12MB3990:EE_|SJ0PR12MB6831:EE_ X-MS-Office365-Filtering-Correlation-Id: 7ca91771-d72e-4e0d-230f-08dd6825e025 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024|10070799003; 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>> + >> + fn add(mut self, rhs: Duration) -> Self::Output { >> + let mut nanos =3D rhs.as_nanos(); >> + while nanos > u64::MAX as u128 { >> + self.0 =3D self.0.wrapping_add(nanos as u64); >> + nanos -=3D u64::MAX as u128; >> + } >> + >> + Timestamp(self.0.wrapping_add(nanos as u64)) >> + } >> +} > > Perhaps I missed something, but couldn=E2=80=99t you simplify this method= like > this: > > fn add(mut self, rhs: Duration) -> Self::Output { > let stamp =3D self.0 as u128; > Timestamp(stamp.wrapping_add(rhs.as_nanos()) as u64) > } You are absolutely right, this loop will just wrap self.0 to the same value after the initial pass. ... or at least it would if there weren't two bugs in it. >_< - It adds the lower part of nanos while substracting u64::MAX from rhs, which is completely wrong; - Substracting u64::MAX is also wrong, it should be u64::MAX as u128 + 1. So thanks a lot for pointing this out!