Am 10.08.2018 um 10:32 schrieb Daniel Vetter: > 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. Yeah, but that is for the userspace API. Not for any internal handling in the driver. Christian. > -Daniel
