virtio_gpu_cmd_resource_flush

[Kasireddy, Vivek]

Hi Josh,

> 
> > If virgl=true (which means blob=false at the moment), then things work
> > very differently.
> Yes, we're using virglrenderer. The flushed resources are backed by host
Virgl is not my forte. Someone working on virgl should be able to help you.

Thanks,
Vivek

> allocated buffers.  We tried posting the flushed resource directly to the
> display and replied to the flush immediately (since not fenced), but I see
> artifacts - I assume the guest is reusing the resource as its being posted.
> 
> So now I'm doing a gpu-blit from the flushed resource into a separate set of
> backbuffers for display.  The blit is done in another thread and I have it
> synchronized so that a second flush can't return until the first flush's
> resource has been copied, making it safe for the guest to reuse.
> 
> This is working ok with a double buffered guest compositor, but its not ideal
> as it can still hold up processing the virtio controlq.  I really need these
> flushes to be fenced so I can defer their response...
> 
> So in my case, what's the best way to handle the flush?
> 
> In case its relevant, at the moment I'm supporting an older virglrenderer that
> doesn't make use of the virtio-v1.2 VIRTIO_GPU_F_RESOURCE_BLOB or
> VIRTIO_GPU_F_CONTEXT_INIT features.
> 
> Thanks,
> Josh