[RFC PATCH 0/8] *** Per context fencing ***

[Gerd Hoffmann]

  Hi,

> >> At virtio level it is pretty simple:  The host completes the SUBMIT_3D
> >> virtio command when it finished rendering, period.
> >>
> >>
> >> On the guest side we don't need the fence_id.  The completion callback
> >> gets passed the virtio_gpu_vbuffer, so it can figure which command did
> >> actually complete without looking at virtio_gpu_ctrl_hdr->fence_id.
> >>
> >> On the host side we depend on the fence_id right now, but only because
> >> that is the way the virgl_renderer_callbacks->write_fence interface is
> >> designed.  We have to change that anyway for per-context (or whatever)
> >> fences, so it should not be a problem to drop the fence_id dependency
> >> too and just pass around an opaque pointer instead.
> 
> I am still catching up, but IIUC, indeed I don't think the host needs
> to depend on fence_id.  We should be able to repurpose fence_id.

I'd rather ignore it altogether for FENCE_V2 (or whatever we call the
feature flag).

> On the other hand, the VIRTIO_GPU_FLAG_FENCE flag is interesting, and
> it indicates that the vbuf is on the host GPU timeline instead of the
> host CPU timeline.

Yep, we have to keep that (unless we do command completion on GPU
timeline unconditionally with FENCE_V2).

cheers,
  Gerd