On 5/18/25 18:26, Yiwei Zhang wrote:
> Venus and later native contexts have their own fence context along with
> multiple timelines within. Fences wtih VIRTIO_GPU_FLAG_INFO_RING_IDX in
> the flags must be dispatched to be created on the target context. Fence
> signaling also has to be handled on the specific timeline within that
> target context.
>
> Before this change, venus fencing is completely broken if the host
> driver doesn't support implicit fencing with external memory objects.
> Frames can go backwards along with random artifacts on screen if the
> host driver doesn't attach an implicit fence to the render target. The
> symptom could be hidden by certain guest wsi backend that waits on a
> venus native VkFence object for the actual payload with limited present
> modes or under special configs. e.g. x11 mailbox or xwayland.
>
> After this change, everything related to venus fencing starts making
> sense. Confirmed this via guest and host side perfetto tracing.
>
> Changes since v1:
> - Minor commit msg updates based on feedbacks from BALATON
>
> Cc: qemu-sta...@nongnu.org
> Fixes: 94d0ea1c1928 ("virtio-gpu: Support Venus context")
> Signed-off-by: Yiwei Zhang <zzyi...@gmail.com>
> ---
> hw/display/virtio-gpu-virgl.c | 44 +++++++++++++++++++++++++++++++++++
> 1 file changed, 44 insertions(+)
>
> diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
> index 145a0b3879..94ddc01f91 100644
> --- a/hw/display/virtio-gpu-virgl.c
> +++ b/hw/display/virtio-gpu-virgl.c
> @@ -970,6 +970,15 @@ void virtio_gpu_virgl_process_cmd(VirtIOGPU *g,
> }
>
> trace_virtio_gpu_fence_ctrl(cmd->cmd_hdr.fence_id, cmd->cmd_hdr.type);
> +#if VIRGL_VERSION_MAJOR >= 1
> + if (cmd->cmd_hdr.flags & VIRTIO_GPU_FLAG_INFO_RING_IDX) {
> + virgl_renderer_context_create_fence(cmd->cmd_hdr.ctx_id,
> +
> VIRGL_RENDERER_FENCE_FLAG_MERGEABLE,
> + cmd->cmd_hdr.ring_idx,
> + cmd->cmd_hdr.fence_id);
> + return;
> + }
> +#endif
> virgl_renderer_create_fence(cmd->cmd_hdr.fence_id, cmd->cmd_hdr.type);
> }
>
> @@ -983,6 +992,11 @@ static void virgl_write_fence(void *opaque, uint32_t
> fence)
> * the guest can end up emitting fences out of order
> * so we should check all fenced cmds not just the first one.
> */
> +#if VIRGL_VERSION_MAJOR >= 1
> + if (cmd->cmd_hdr.flags & VIRTIO_GPU_FLAG_INFO_RING_IDX) {
> + continue;
> + }
> +#endif
Is it possible that virglrenderer will ever write a context fence in
virgl_renderer_create_fence()? Do we really need this check?
--
Best regards,
Dmitry
