ubuntu-x-swat team mailing list archive

[Bryce Harrington <316514@xxxxxxxxxxxxxxxxxx>]

** Summary changed:

- MASTER:  Xinerama/Multihead with several video cards is not supported
+ MASTER:  Xinerama/Multihead with multiple video cards is not supported for most video drivers

** Description changed:

  Binary package hint: xorg
  
  [Problem]
  X does not support (or does not support very well) displaying a desktop across more than one video card.  When it is possible, a variety of bugs are experienced.
  
  [Discussion]
  Prior to the introduction of Xrandr it was (sometimes) possible to configure xorg.conf to display on multiple video cards.  One could then use Xinerama, etc. to stitch screens into a contiguous desktop.  Of course, any alterations to this setup usually required hand-tuning xorg.conf.
  
  The introduction of Xrandr made a number of things much easier, however
  it is not good at handling the case of multiple video cards.  It can
  handle dual-head displays, where both monitors are connected to separate
  outputs on the same video card, but does not work as well with outputs
  on two different cards.
  
  The fundamental problem (as I understand it) is essentially that X can
  talk to only one physical "pool" of memory, and each card has its own
  physical pool.  Recent developments including GEM and several kernel
  changes promise to remedy this by enabling these pools to be aggregated
  and managed as a single virtual pool.  Once the X server and drivers are
  updated to utilize this new architecture, they should be able to support
  multi-card functionality with Xrandr as well as (and better than) the
  old Xinerama configuration, including reconfiguring the display without
  needing to edit xorg.conf or restart X.
  
  [Exceptions]
  As mentioned above, the problem is most notable with drivers that have switched from Xinerama to Xrandr.  If you're using an older driver that still uses the old Xinerama approach, you *might* find it works acceptably.
  
  In my own testing, I've found cases where I could get displays across
  multiple cards (separate screens per-card) when running xrandr, but I
  ran into so many different bugs (mouse not working properly, X crashing,
  display corruption, etc.) that it was essentially unusable.  Even if it
  could be made to work, this configuration is quite non-standard and not
  well tested.  Resolving those issues will likely wait until the
  aforementioned architecture is fully in place.
+ 
+ The closed source -nvidia driver still uses Xinerama (it never got
+ around to implementing Xrandr), so you can achieve multiple head
+ displays that way.  The nvidia configuration tool will be able to
+ construct the xorg.conf settings for you to achieve Xinerama multi-head.

-- 
MASTER:  Xinerama/Multihead with multiple video cards is not supported for most video drivers
https://bugs.launchpad.net/bugs/316514
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