[Intel-gfx] [iGVT-g] Ask for comments of getting guest framebuffer in igvt-g

[Gerd Hoffmann]

  Hi,

> btw I don't think this vblank issue would be very significant. The main
> targeted usage of GVT-g is for server virtualization/cloud, where 
> a remoting protocol is required for customer to see the content through
> network.

The plan for that is to let the gpu video encoder process the guest
framebuffer.  So the video encoder still being busy processing the
buffer while the guest already started updating it can certainly lead to
visible tearing.

I think using vblank to signal the guest when the host is done
processing the framebuffer makes sense.  It'll simply throttle the guest
in case the host is too busy to keep up.

Storing the guest framebuffer via blit somewhere else, just to allow the
guest render at full frame rate even if the host isn't able to process
the frames fast enough looks pointless to me.  We are simply wasting gpu
cycles then.

cheers,
  Gerd