On Wed, 2020-03-11 at 12:31 -0500, Jason Ekstrand wrote: > - X11: With present, it has these "explicit" fence objects but > they're always a shmfence which lets the X server and client do a > userspace CPU-side hand-off without going over the socket (and > round-tripping through the kernel). However, the only thing that > fence does is order the OpenGL API calls in the client and server and > the real synchronization is still implicit. I'm pretty sure "the only thing that fence does" is an implementation detail. PresentPixmap blocks until the wait-fence signals, but when and how it signals are properties of the fence itself. You could have drm give the client back a fence fd, pass that to xserver to create a fence object, and name that in the PresentPixmap request, and then drm can do whatever it wants to signal the fence. > From my perspective, as a Vulkan driver developer, I have to deal with > the fact that Vulkan is an explicit sync API but Wayland and X11 > aren't. I'm quite sure we can give you an explicit-sync X11 API. I think you may already have one. - ajax
