On 2021-05-19 5:21 p.m., Jason Ekstrand wrote: > On Wed, May 19, 2021 at 5:52 AM Michel Dänzer <mic...@daenzer.net> wrote: >> >> On 2021-05-19 12:06 a.m., Jason Ekstrand wrote: >>> On Tue, May 18, 2021 at 4:17 PM Daniel Vetter <dan...@ffwll.ch> wrote: >>>> >>>> On Tue, May 18, 2021 at 7:40 PM Christian König >>>> <ckoenig.leichtzumer...@gmail.com> wrote: >>>>> >>>>> Am 18.05.21 um 18:48 schrieb Daniel Vetter: >>>>>> On Tue, May 18, 2021 at 2:49 PM Christian König >>>>>> <ckoenig.leichtzumer...@gmail.com> wrote: >>>>>> >>>>>>> And as long as we are all inside amdgpu we also don't have any oversync, >>>>>>> the issue only happens when we share dma-bufs with i915 (radeon and >>>>>>> AFAIK nouveau does the right thing as well). >>>>>> Yeah because then you can't use the amdgpu dma_resv model anymore and >>>>>> have to use the one atomic helpers use. Which is also the one that >>>>>> e.g. Jason is threathening to bake in as uapi with his dma_buf ioctl, >>>>>> so as soon as that lands and someone starts using it, something has to >>>>>> adapt _anytime_ you have a dma-buf hanging around. Not just when it's >>>>>> shared with another device. >>>>> >>>>> Yeah, and that is exactly the reason why I will NAK this uAPI change. >>>>> >>>>> This doesn't works for amdgpu at all for the reasons outlined above. >>>> >>>> Uh that's really not how uapi works. "my driver is right, everyone >>>> else is wrong" is not how cross driver contracts are defined. If that >>>> means a perf impact until you've fixed your rules, that's on you. >>>> >>>> Also you're a few years too late with nacking this, it's already uapi >>>> in the form of the dma-buf poll() support. >>> >>> ^^ My fancy new ioctl doesn't expose anything that isn't already >>> there. It just lets you take a snap-shot of a wait instead of doing >>> an active wait which might end up with more fences added depending on >>> interrupts and retries. The dma-buf poll waits on all fences for >>> POLLOUT and only the exclusive fence for POLLIN. It's already uAPI. >> >> Note that the dma-buf poll support could be useful to Wayland compositors >> for the same purpose as Jason's new ioctl (only using client buffers which >> have finished drawing for an output frame, to avoid missing a refresh cycle >> due to client drawing), *if* it didn't work differently with amdgpu. >> >> Am I understanding correctly that Jason's new ioctl would also work >> differently with amdgpu as things stand currently? If so, that would be a >> real bummer and might hinder adoption of the ioctl by Wayland compositors. > > My new ioctl has identical semantics to poll(). It just lets you take > a snapshot in time to wait on later instead of waiting on whatever > happens to be set right now. IMO, having identical semantics to > poll() isn't something we want to change.
Agreed. I'd argue then that making amdgpu poll semantics match those of other drivers is a pre-requisite for the new ioctl, otherwise it seems unlikely that the ioctl will be widely adopted. -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer
