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Thread: 2x ATI 5670 & 3 Monitors - How?

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  1. #1
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    Question 2x ATI 5670 & 3 Monitors - How?

    Hi All,

    I have done a bit of googling on this, but haven't found a solution yet (just dissatisfied 'customers'). What I would like to be able to do is run 3 monitors on 2 ATI 5670's.

    So far I got 2 of the monitors working on one card with fglrx, but the driver doesn't seem to find the other card (just says unknown on the 3rd monitor.)

    Is there some switch I missed? Or do I need to go over to the open source driver?

    Anyone got experience with a 3 Monitor/2 ATI card setup?

  2. #2
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    Have you already managed to have X working with each monitor at a single time?

    I know how to have triple head using 2 ATI cards using xinerama (no direct rendering), but I guess eyefinity enabled cards can do triple head with direct rendering. At least, that's what I see in this video: http://www.youtube.com/watch?v=N6Vf8R_gOec.

  3. #3
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    Ok. Figured it out. After a quick 'sudo aticonfig --adapter=all --initial' I got the second card working.

    The only thing is that compiz is turned off because of Xinerama (needed to drag across all three sceens). The 2D is somewhat choppy, but it's working.


  4. #4
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    There used to be an aticonfig option (-all ?) that was required to initialize multiple adapters. Not sure if it is still required but check the end of aticonfig --help output.

    Many Evergreen cards will drive 3 displays off a single GPU if you use a DP-to-whatever adapter for the third display.

    EDIT - looks like we crossed in the mail, never mind - glad you got it running.

  5. #5
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    Thanks bridgman.

    Yeah, it seems to run 3 displays now, but the latest is that it crashes X as soon as I open a window and try to click on anything.

    Not sure what is going on.

  6. #6
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    Ok, turning OFF xinerama seems to stop the madness. I tried opening ccc and everytime I HOVER over the window, X would crash.

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    Were those crashes before you turned off Xinerama or after ?

  8. #8
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    Quote Originally Posted by bridgman View Post
    Were those crashes before you turned off Xinerama or after ?
    Before. After I turned it off, everything was working fine. Found a thread that mentioned that Xinerama with more than 3 monitors will crash X (with nvidia as well).

    I now purged the fglrx driver and switched back to the open source driver. Found a xorg.conf online that someone got working with XRandR and 3 monitors. Just changed it to fit my setup and I am up and running with 3 monitors and the open source driver.

  9. #9
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    bridgman, here is the link to the thread: http://ubuntuforums.org/showthread.php?t=1489377

    If you go down a few posts, you'll see that there are a few that have issues with Xinerama.

    I am now realizing (never had a 3 monitor setup before) that Xinerama is a pile of poo. Not even compiz can be enabled when you have more than 2 monitors (neither ATI, nor nvidia).

    Hopefully Wayland will give Linux the edge it really needs. X is antiquated.

  10. #10
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    Quote Originally Posted by gtrawoger View Post
    Hopefully Wayland will give Linux the edge it really needs. X is antiquated.
    I love the uninformed "Wayland will make everything better!"-hype

    Xinerama is a very old attempt at multi-GPU-rendering from the last millenium, where multi-GPU cards didn't exist yet. It was designed to work in the use cases common during that time.
    Basically your desktop is divided by monitors, and each GPU is responsible for all drawing operations that occur on it's own monitor.
    This works well in cases where your applications are mostly restricted to a single monitor, but still allows you to drag a window to a different monitor when needed - the application and all it's textures and pixmaps are moved to the other GPU and it continues to run there.

    There are limits to the solution Xinerama chooses: applications spanning multiple monitors, like fullscreen games or even a window sitting between two monitors. Now all rendering commands must be performend by both GPUs. Each GPU will only render half the window, but fillrate is rarely the bottleneck. Using Xinerama, these use cases are always *slower* with 2 GPUs than with one, which somewhat defeats the purpose of a modern multi-GPU system.

    Then along came compositing: now your application does not live on a monitor any more, it's just a texture somewhere in video memory, waiting to be copied by the compositor. Which of the GPUs should be responsible?
    And the compositor is a fullscreen application with all the caveats listed in the previous paragraph.


    Xinerama was never meant to satisfy these use cases, it is the wrong solution, and it's not surprising that nobody really cares to maintain it or to fix bugs that arise from compositing. In fact, Xinerama is officially deprecated.
    (that said, your specific bug is already fixed.)


    Back my favourite topic, Wayland. Wayland will magically solve everything, bring world peace and give us free puppies.
    Unfortunately, it doesn't even have a multi-GPU solution. None at all. Works even less than Xinerama.


    Yes, linux needs a good multi-GPU solution that satisfies modern needs, but this is anything but trivial. There have been some attempts to hack something up, but it's a lot of work to get all the corner cases right, and AFAIK it's not high on the priority lists of any major contributor.
    It's likely that any multi-GPU solution would end up somewhere in the DRI stack, thus outside of X or Wayland. If a multi-GPU solution arrives in the future, it can be expected to work equally well for both display systems.


    Now you know why your specific setup cannot work as well as you hope, why it won't work as well as you hope for the near future, and why wayland really shouldn't give you any hope at all. Did I manage to spread some christmas cheer


    (seriously: get an active (!) DP->DVI adapter and toss out the second GPU, it'll make things way easier for you.)

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