General Discussions

[crashdog]

Hello,

In my setup I have 2 AMD Vega 64 graphics cards. Both cards are recognized by the system/driver. I can see them in the system page in the AMD Radeon Settings.

But only the primary card recognizes display port screens (have not tried hmdi). I do not have Cross Fire or any linking installed.

Is this a normal behavior ? In my mind the load on the graphic cards are better distributed when each screen is connected to it's own card.

Kind Regards,

Gerhard

[black_zion]

In Radeon Settings under System what does it say? (Primary/Linked adapter, Primary/Disabled adapter, Primary/Secondary adapter, etc)

[crashdog]

It says:

Primary/Master/Descrete and Linked/Discrete.

Does that mean the second cards is sort of "slave" linked to the primary ?

[black_zion]

Linked means Crossfire is enabled and outputs on the second card are disabled.

[crashdog]

Interessting.. I always though Crossfire needs a special cable directly between the graphic cards. Also that in Crossfire mode only one screen works.

Is Crossfire the recomended mode of operation ? or will performace improve on multi monitor setups if it's diabled ?

[arcticwind]

In crossfire, all monitors should be connected to the primary GPU.

From Wikipedia...

GPUs using newer versions of GCN no longer have bridging ports. Instead, they use XDMA to open a direct channel of communication between the multiple GPUs in a system, operating over the same PCI Express bus which is used by AMD Radeon graphics cards.^{[14][15][16][17]}

PCI Express 3.0 lanes provide to up to 17.5 times higher bandwidth (15.754 GB/s for a ×16 slot) when compared to current external bridges (900 MB/s), rendering the use of a CrossFire bridge unnecessary. Thus, XDMA was selected for greater GPU interconnection bandwidth demands generated by AMD Eyefinity, and more recently by 4K resolution monitors. Bandwidth of the data channel opened by XDMA is fully dynamic, scaling itself together with the demands of the game being played, as well as adapting to advanced user settings such as vertical synchronization (vsync).^[14][18]

[black_zion]

AMD ditched the ribbon cable years ago. Attach both display cables to the top card and it'll work just fine.