[Feature request] Multiple X servers on one graphics card?

[Alex Deucher]

On Tue, Aug 2, 2011 at 10:22 AM, Prof. Dr. Klaus Kusche
<klaus.kusche at computerix.info> wrote:
> On 2011-08-02 14:59, Alex Deucher wrote:
>>
>> On Mon, Aug 1, 2011 at 3:41 PM, Prof. Dr. Klaus Kusche
>> <klaus.kusche at computerix.info>  wrote:
>>>
>>> Hmmm, what's about the opposite approach?
>>> To me, it sounds simpler and more logical when the kernel always creates
>>> one device node per output (or maybe dynamically per connected output),
>>> without any need for configuration or device assignment.
>>
>> You almost always have more connectors than display controllers (e.g.,
>> you might have displayport, svideo, DVI-I and VGA, but only two
>> display controllers so you can only use two of the connectors at any
>> time).  Also certain combinations of connectors are not possible
>> depending on the hw (e.g., the svideo and the VGA port may share the
>> same DAC, so you can only use one or the other at the same time).
>
> Hmmm, for my purposes I was only thinking about new, current hardware,
> not about previous-generation cards, and only about digital outputs:
>
> * The professional, high-quality solution would be ATI's FirePro 2460:
> 4 mini Displayports, all active at the same time, single slot
> (passive cooling, < 20 W, so that's a great energy saver, too,
> competing with thin and zero clients,
> and it's silent and long-lived)
>
> * The XFX HD-677X-Z5F3 most likely offers most ports per Euro and space:
> 5 mini Displayports, all active at the same time, single slot,
> for less than 100 Euro
>
> (this would result in 16/20 seats with any quad-crossfire mainboard
> and 28/35 seats with some server mainboards if the BIOS is able
> to assign addresses to 7 graphics cards)
>
> Even the low-cost 6450 supports 3 and the 6570 supports 4
> independent simultaneous outputs, so any ATI 6xxx card can drive
> all its outputs at the same time
> (and I believe that was also true for ATI 5xxx)
> However, cards with 3 or 4 digital outputs are hard to find
> in that price range... (XFX HD6570 is one of them)
>
> But you're correct, my suggestion above needs to be refined:
> One DRI device per display controller.

Even then it gets a little tricky.  AMD cards are fairly flexible, but
some other cards may have restrictions about which encoders can be
driven by which display controllers.  Then how do you decide which
display controller gets assigned to which connector(s)?  You also need
to factor in things like memory bandwidth.  E.g., a low end card may
not be able to drive four huge displays properly, but can drive four
smaller displays.

Alex