Wayland For Very Large Wall of Screens

Daniel Stone daniel at fooishbar.org
Thu Oct 2 15:21:31 PDT 2014


On 2 October 2014 23:13, Dave Airlie <airlied at gmail.com> wrote:

> On 1 October 2014 03:15, Daniel Stone <daniel at fooishbar.org> wrote:
> > On 30 September 2014 16:44, Jasper St. Pierre <jstpierre at mecheye.net>
> wrote:
> >> It's a great question, with a complicated answer. Part of this is the
> >> fault of the DRM kernel interface, which is being improved. Part of it
> is
> >> the fault of GL/EGL, which really doesn't have proper multi-GPU support.
> Also there is a good reason Windows doesn't work with multiple
> graphics cards anymore that aren't from the same vendor and in the
> same general class of chip.
> For running a wall of lots of monitors or you need multiple ATI or
> multiple NVIDIA cards, getting anything else to function in a rational
> manner isn't supported or at least wasn't last I look.
> Since you have a compositor running you no longer have the knowledge
> of on-screen clipping to say where to direct rendering,
> There is unfortunately no "nice" solution to this problem, under X or
> wayland, except making apps that are aware of the problem and use
> interface provided to solve it.
> You also have the optimus style solutions, which is run everything on
> one GPU and just use the other GPUs as slave outputs.

Yeah, actually exploding them is a very difficult problem. Especially in a
system like Wayland rather than X11, where we don't hand out global
co-ordinates, so we can't just say 'this chunk is on this GPU, that chunk
on that GPU, ...'. We'd need a way to explode the surfaces in such a way
that you could atomically attach multiple buffers, plus compositor support
for ensuring coherent presentation of all those buffers, and then try to
keep the display controller side of things as tight as possible, which if
you're doing media or moving anything around between outputs, really means
cross-device genlock.

Long short short, there's nothing in Wayland that precludes it, but it
really is the very very least of your problems.

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