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Wed, 12 Nov 2025 00:45:58 +0000 Received: from CH2PR12MB3990.namprd12.prod.outlook.com ([fe80::7de1:4fe5:8ead:5989]) by CH2PR12MB3990.namprd12.prod.outlook.com ([fe80::7de1:4fe5:8ead:5989%6]) with mapi id 15.20.9298.015; Wed, 12 Nov 2025 00:45:58 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 12 Nov 2025 09:45:53 +0900 Message-Id: To: "Lyude Paul" , "Joel Fernandes" , "Timur Tabi" , "John Hubbard" Cc: "dakr@kernel.org" , "lossin@kernel.org" , "ojeda@kernel.org" , "boqun.feng@gmail.com" , "a.hindborg@kernel.org" , "simona@ffwll.ch" , "tmgross@umich.edu" , "alex.gaynor@gmail.com" , "mripard@kernel.org" , "linux-kernel@vger.kernel.org" , "maarten.lankhorst@linux.intel.com" , "dri-devel@lists.freedesktop.org" , "nouveau@lists.freedesktop.org" , "rust-for-linux@vger.kernel.org" , "gary@garyguo.net" , "bjorn3_gh@protonmail.com" , "tzimmermann@suse.de" , "airlied@gmail.com" , "aliceryhl@google.com" , "Alexandre Courbot" , "joel@joelfernandes.org" , "Alistair Popple" , "Nouveau" Subject: Re: [PATCH v2 08/12] nova-core: sequencer: Add register opcodes From: "Alexandre Courbot" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20251102235920.3784592-1-joelagnelf@nvidia.com> <20251102235920.3784592-9-joelagnelf@nvidia.com> <0FF9536C-8740-42C3-8EF1-5C8CD5520E49@nvidia.com> <93c758298250d2be9262256a698c243343b64ebc.camel@nvidia.com> <3c625930-348a-4c96-a63a-6a3e98e59734@nvidia.com> <80e57b47579df4cb603205935cc5e46fcb0eb409.camel@redhat.com> In-Reply-To: <80e57b47579df4cb603205935cc5e46fcb0eb409.camel@redhat.com> X-ClientProxiedBy: TY4PR01CA0118.jpnprd01.prod.outlook.com (2603:1096:405:379::15) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|DS7PR12MB6069:EE_ X-MS-Office365-Filtering-Correlation-Id: d2628ac1-cb42-4e8d-d745-08de2184d824 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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I've tried. >> >=20 >> > This works great for me: >> >=20 >> > modprobe nouveau dyndbg=3D"+p" modeset=3D1 debug=3D"gsp=3Dspam" config= =3DNvGspRm=3D1 >> >=20 >> > I get all sequencer messages when I boot with these options. >> >=20 >> > > ftrace/bpftrace, maybe those are the real way to "trace"...or someth= ing >> > > other than this. >> >=20 >> > You could say the same thing about most dev_dbg() statements. >> >=20 >> > I agree that dev_dbg for sequencer commands is excessive, and that imp= lementing new debug levels >> > just to get sequencer prints is also excessive. But Nouveau implement= nvkm_trace for a reason. And >> > we all know that because of ? in Rust, NovaCore does a terrible job at= telling us where an error >> > actually occurred. So there is a lot of room for improvement. >>=20 >> IMO, the best way to do this is the tracing subsystem. It is the lowest = overhead >> runtime kernel logging system that I know off, lockless, independent of = the >> serial console etc, next to no runtime overhead when off, etc. >>=20 > > I agree. FWIW, it's worth noting that honestly avoiding logging is the wa= y to > go for anything spammy. I've seen quite a number of heisenbugs that only > appear when trace logging isn't turned on in nouveau or vice-versa (igt t= ests > that fail because logging causes things to time out=E2=80=A6). +1 for tracing, when debugging we are typically interested in a very small subset of the debug logs and the ability to only enable what is needed is essential. Though I am not sure about the current state of tracing support in Rust...