[Libdlo] Ubuntu 9.10 report

[Bernie Thompson]

On Tue, Nov 3, 2009 at 2:39 PM, Luke Kenneth Casson Leighton
<lkcl at lkcl.net> wrote:
>  i was thinking of running qemu direct onto fbdev screens.
>  on the ARM boards, that would mean being able to run Wince
>  on one screen, Android on another, ubuntu on a third etc.
>  with the upcoming Cortex A9 dual-core ARM, expected to top out
>  at 2ghz, that's perfectly reasonable.

Hi Luke,

It'll be great to have some information on how well that works -- it's
a great scenario.  I've not used qemu yet, but have used vmware, which
virtualizes USB 2.0 at a low level well enough that DisplayLink
devices functionally work transparently over it -- so in the past I've
had Windows running as host, and tested connecting/assigning
DisplayLink devices to individual VMs (thus giving each ownership of
their own graphics device/screen) running Linux and other OSes, and it
worked surprisingly well.  qemu direct to fbdev should be way more
efficient/quick.

One note, though -- that I'm not sure udlfb or displaylink-mod yet
trigger the way you'd expect to direct framebuffer writes.
displaylinkfb (Jaya's driver), however, does automatical trigger via
page faults.

> so - bernie, how does the data efficiency of the displaylink algorithm
> compare with VNC for example?

They're designed with different constraints, including type of network
(DisplayLink's works great over "networks" like USB bulk) and ease of
implementation in hardware, so it's hard to compare.  If you have a
general purpose CPU on both ends, practically you're probably better
off using VNC over the network, then DL to the screen.  Ndiyo actually
has played with both models, and still finds using VNC convenient.  In
May Quentin contributed a VNC client which natively renders to DL
devices via libdlo
http://lists.freedesktop.org/archives/libdlo/2009-May/000067.html .
libdlo just needs a little love to make it performant.  Again, another
great scenario to prove out.

Best wishes,
Bernie