On Fri, Aug 10, 2018 at 10:24 AM, Christian König <christian.koenig at amd.com> wrote: > Am 10.08.2018 um 09:51 schrieb Chris Wilson: >> >> Quoting Christian König (2018-08-09 15:54:31) >>> >>> Am 09.08.2018 um 16:22 schrieb Daniel Vetter: >>>> >>>> On Thu, Aug 9, 2018 at 3:58 PM, Christian König >>>> <ckoenig.leichtzumerken at gmail.com> wrote: >>>>> >>>>> Am 09.08.2018 um 15:38 schrieb Daniel Vetter: >>>>>> >>>>>> On Thu, Aug 09, 2018 at 01:37:07PM +0200, Christian König wrote: >>>>>> [SNIP] >>>>> >>>>> See to me the explicit fence in the reservation object is not even >>>>> remotely >>>>> related to implicit or explicit synchronization. >>>> >>>> Hm, I guess that's the confusion then. The only reason we have the >>>> exclusive fence is to implement cross-driver implicit syncing. What >>>> else you do internally in your driver doesn't matter, as long as you >>>> keep up that contract. >>>> >>>> And it's intentionally not called write_fence or anything like that, >>>> because that's not what it tracks. >>>> >>>> Of course any buffer moves the kernel does also must be tracked in the >>>> exclusive fence, because userspace cannot know about these. So you >>>> might have an exclusive fence set and also an explicit fence passed in >>>> through the atomic ioctl. Aside: Right now all drivers only observe >>>> one or the other, not both, so will break as soon as we start moving >>>> shared buffers around. At least on Android or anything else using >>>> explicit fencing. >>> >>> Actually both radeon and nouveau use the approach that shared fences >>> need to wait on as well when they don't come from the current driver. >> >> nouveau has write hazard tracking in its api , and is using the >> excl fence for it was well. >> >> As far as I can tell, this is all about fixing the lack of >> acknowledgement of the requirement for implicit fence tracking in >> amdgpu's (and its radeon predecessor) ABI. > > > Well I agree that implicit fencing was a bad idea to begin with, but the > solution you guys came up with is not going to work in all cases either. > >> Which is fine so long as you >> get userspace to only use explicit fence passing to the compositor. > > > Well exactly that's the problem. > > I can't pass exactly one explicit fence to the compositor because I have > multiple command submissions which run asynchronously and need to finish > before the compositor can start to use the surface. > > So the whole concept of using a single exclusive fence doesn't work in the > case of amdgpu. And to be honest I think all drivers with multiple engines > could benefit of that as well. Fences can be merge. This works, really :-) In amdgpu's implementation of EGL_ANDROID_native_fence_sync you will need to do that before passing the result to the caller. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
