[Spice-devel] [PATCH RFC 00/12] Remote Virgl support

[Gerd Hoffmann]

  Hi,

> > Hmm.  The guest will not give us 2-3 frames though.  We'll have either
> > one or two, depending on whenever the guest uses page-flips or not.  So
> > implementing a buffering scheme as outlined above requires us to copy
> > (or let the gpu copy) the frames.

> Probably 2 are enough, 1 I have to think about it, there may be some
> possible timing problems. What happens if single frame processing
> take too much? Does guest slow down?

Oops, I think I have to correct myself.  You get one frame, period.
Yes, the guest will slow down.  Right now we stop all virgl rendering
until spice signals it is done via QXL_COOKIE_TYPE_GL_DRAW_DONE, to make
sure the user will not see half-rendered frames.

Without page-flipping this is pretty much the only thing we can do.

With page-flipping we can parallelize things a bit: The guest can render
into one frame while spice process the other one.  It isn't implemented
today though[1].  Implementing it will not give additional frames for
queuing, we will get less guest throttling instead.

cheers,
  Gerd

[1] we have to block virgl rendering to current scanout only,
    instead of blocking all virgl rendering.