Introduction and updates from NVIDIA

[Miguel Angel Vico]

On Wed, 6 Apr 2016 13:14:26 +0100
Daniel Stone <daniel at fooishbar.org> wrote:

> Hi,
> 
> On 6 April 2016 at 09:41, Jonas Ådahl <jadahl at gmail.com> wrote:
> > On Mon, Apr 04, 2016 at 04:27:56PM +0100, Daniel Stone wrote:  
> >> Again this comes down to the synchronisation. In this case,
> >> assuming a mailbox stream:
> >>   - wl_egl_surface_resize(w1, h1)
> >>   - gl*()
> >>   - eglSwapBuffers() <- commit 1
> >>   - wl_egl_surface_resize(w2, h2)
> >>   - gl*()
> >>   - eglSwapBuffers() <- commit 2
> >>
> >> For this, you would need some kind of synchronisation, to ensure
> >> that processing commit 1 didn't pick up on the differently-sized
> >> frames for commit 2.  
> >
> > Just to point out the obvious, using wl_egl_surface_resize as a
> > barrier/separator/synchronization-triggerer is not enough for this.
> > The mailbox vs FIFO mode needs to be tightly coupled with subsurface
> > asynchronous/synchronous mode. For example, ignoring the resize
> > calls in the above code, commit 1 and commit 2 might have drawn UI
> > elements that are expected to be aligned with subsurface that were
> > moved.  
> 
> Yep, subsurface in particular. It sounds like FIFO mode will DTRT with
> some adjustments to the patches, but I just can't for the life of me
> see how mailbox mode would work properly in all cases. You'd really
> need some kind of explicit synchronisation barriers with the
> compositor in order to determine when it was safe to replace one frame
> with a newer frame.

Agree. Mailbox mode is something we are aware we need to revisit for
this particular use case.

> 
> Cheers,
> Daniel


-- 
Miguel