On Tue, 21 Jul 2020 at 18:47, Thomas Hellström (Intel) <thomas_os@xxxxxxxxxxxx> wrote: > > > On 7/21/20 9:45 AM, Christian König wrote: > > Am 21.07.20 um 09:41 schrieb Daniel Vetter: > >> On Mon, Jul 20, 2020 at 01:15:17PM +0200, Thomas Hellström (Intel) > >> wrote: > >>> Hi, > >>> > >>> On 7/9/20 2:33 PM, Daniel Vetter wrote: > >>>> Comes up every few years, gets somewhat tedious to discuss, let's > >>>> write this down once and for all. > >>>> > >>>> What I'm not sure about is whether the text should be more explicit in > >>>> flat out mandating the amdkfd eviction fences for long running compute > >>>> workloads or workloads where userspace fencing is allowed. > >>> Although (in my humble opinion) it might be possible to completely > >>> untangle > >>> kernel-introduced fences for resource management and dma-fences used > >>> for > >>> completion- and dependency tracking and lift a lot of restrictions > >>> for the > >>> dma-fences, including prohibiting infinite ones, I think this makes > >>> sense > >>> describing the current state. > >> Yeah I think a future patch needs to type up how we want to make that > >> happen (for some cross driver consistency) and what needs to be > >> considered. Some of the necessary parts are already there (with like the > >> preemption fences amdkfd has as an example), but I think some clear docs > >> on what's required from both hw, drivers and userspace would be really > >> good. > > > > I'm currently writing that up, but probably still need a few days for > > this. > > Great! I put down some (very) initial thoughts a couple of weeks ago > building on eviction fences for various hardware complexity levels here: > > https://gitlab.freedesktop.org/thomash/docs/-/blob/master/Untangling%20dma-fence%20and%20memory%20allocation.odt We are seeing HW that has recoverable GPU page faults but only for compute tasks, and scheduler without semaphores hw for graphics. So a single driver may have to expose both models to userspace and also introduces the problem of how to interoperate between the two models on one card. Dave.
