[Wayland-bugs] [Bug 98766] We need fences support in Wayland compositors

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98766

--- Comment #9 from James Jones <jajones at nvidia.com> ---
Yes, the overhead is in the ioctls needed to instantiate a sync object into a
usermode driver or another command queue in our kernel driver.  It's relatively
expensive on NV hardware when not using a global GPU virtual address space.

There's an API to import general Vulkan sync primitives (Including dma
fences/sync FDs, but also persistent-style Vulkan semaphores) directly to GL
via the GL/Vulkan interop extensions which I believe Mesa supports.

KMS may need sync FDs, but not all compositing happens in KMS.  There's also
the hypothetical-at-this-point Vulkan-only compositor implementation that
doesn't use KMS.  Having Weston/Mesa/Mutter/etc. support only KMS and even only
sync FDs/dma-fences is the current design norm, but baking that assumption in
the protocol is another thing.  The core wayland protocols aimed for platform
independence, and this seems like something that's likely to become a
relatively central concept in Wayland frame delivery in the future.

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