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Fri, 10 Jul 2020 14:23:51 +0000 Date: Fri, 10 Jul 2020 11:23:47 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: Christian =?utf-8?B?S8O2bmln?= , DRI Development , Intel Graphics Development , linux-rdma , Felix Kuehling , kernel test robot , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , Mika Kuoppala , "open list:DMA BUFFER SHARING FRAMEWORK" , "moderated list:DMA BUFFER SHARING FRAMEWORK" , amd-gfx list , Chris Wilson , Maarten Lankhorst , Daniel Vetter Subject: Re: [PATCH 02/25] dma-fence: prime lockdep annotations Message-ID: <20200710142347.GE23821@mellanox.com> References: <20200707201229.472834-1-daniel.vetter@ffwll.ch> <20200707201229.472834-3-daniel.vetter@ffwll.ch> <20200709080911.GP3278063@phenom.ffwll.local> <20200710124357.GB23821@mellanox.com> <5c163d74-4a28-1d74-be86-099b4729a2e0@amd.com> <20200710125453.GC23821@mellanox.com> <4f4a2cf7-f505-8494-1461-bd467870481e@amd.com> <20200710134826.GD23821@mellanox.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BL1PR13CA0060.namprd13.prod.outlook.com (2603:10b6:208:257::35) To VI1PR05MB4141.eurprd05.prod.outlook.com (2603:10a6:803:44::15) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (156.34.48.30) by BL1PR13CA0060.namprd13.prod.outlook.com (2603:10b6:208:257::35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3195.9 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: cppyrSEFdAgkQ1i7W9q/voX0DbtbyyOVjwrEIOo4B7uYYODS8hmJEImRWNNtUiiOZNbaGtDnkKXCJRabgq7Bp4V5pamVdLqGNBMZzoizlzvRIc4PSgtdlF+13VePfAl+oWKQk9qlVh9blVl6PeuQYddj/USevZucky7iGVoqrg2GZ5DN2jMpZhpOaAXMbPu2PunbQ5KcLnjeYp1oJ5ZFWvNgBeIsmktajZlGxvfjkOhMNcqpA0LNpCo5GIpwIT52tIiYKLwRLQ0phw422o6y72JoJWSAwKGLaxj+zVWRs9pmtw6lHvYZwCwaoBSM2OZQeoLsZ7j0uncXth5RBLfm+/2Bv3rmRL42O8pmdQQ2NsxdQPoCFIy/30Yb5MD2tdELN2LR1o4k3i7R1AdJsyZqLM5BvRmDpRJbdg3Nwu/FEhp378GOFB8T6hAOnKknTA8vl95ONAs2NyV2N0CubuBtYkdKjh39nFGqTwJCU9QwM2Q= X-OriginatorOrg: Mellanox.com X-MS-Exchange-CrossTenant-Network-Message-Id: 765aa671-94f1-4fce-ce18-08d824dcde35 X-MS-Exchange-CrossTenant-AuthSource: VI1PR05MB4141.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Jul 2020 14:23:51.4197 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: zwF71M+iqtNMffEf9NDildz9GQ391BR6YYfGlkhI/j0w0yOozGHG4f48p0kC5CNi1e2iLtFsRIITXUxwN0ma/A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR05MB5583 Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Fri, Jul 10, 2020 at 04:02:35PM +0200, Daniel Vetter wrote: > > dma_fence only possibly makes some sense if you intend to expose the > > completion outside a single driver. > > > > The prefered kernel design pattern for this is to connect things with > > a function callback. > > > > So the actual use case of dma_fence is quite narrow and tightly linked > > to DRM. > > > > I don't think we should spread this beyond DRM, I can't see a reason. > > Yeah v4l has a legit reason to use dma_fence, android wants that > there. 'legit' in the sense the v4l is supposed to trigger stuff in DRM when V4L DMA completes? I would still see that as part of DRM Or is it building a parallel DRM like DMA completion graph? > > Trying to improve performance of limited HW by using sketchy > > techniques at the cost of general system stability should be a NAK. > > Well that's pretty much gpu drivers, all the horrors for a bit more speed :-) > > On the text itself, should I upgrade to "must not" instead of "should > not"? Or more needed? Fundamentally having some unknowable graph of dependencies where parts of the graph can be placed in critical regions like notifiers is a complete maintenance nightmare. I think building systems like this should be discouraged :\ Jason