[Mesa-dev] [PATCH 0/7] dma-buf: Add an API for exporting sync files (v11)

[Chia-I Wu]

On Tue, May 25, 2021 at 2:18 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
> Modern userspace APIs like Vulkan are built on an explicit
> synchronization model.  This doesn't always play nicely with the
> implicit synchronization used in the kernel and assumed by X11 and
> Wayland.  The client -> compositor half of the synchronization isn't too
> bad, at least on intel, because we can control whether or not i915
> synchronizes on the buffer and whether or not it's considered written.
We might have an important use case for this half, for virtio-gpu and Chrome OS.

When the guest compositor acts as a proxy to connect guest apps to the
host compositor, implicit fencing requires the guest compositor to do
a wait before forwarding the buffer to the host compositor.  With this
patch, the guest compositor can extract the dma-fence from the buffer,
and if the fence is a virtio-gpu fence, forward both the fence and the
buffer to the host compositor.  It will allow us to convert a
guest-side wait into a host-side wait.