What is required for a game (engine) to support multi GPU(s) systems (because it suppose to be quite

[Calin Banc]

Although a lot of games don't support this or the scaling is bad, it seems our friends at Bohemia consider that having SLI or CF in your game is quite easy: http://steamcommunity.com/app/107410/discussions/0/458606248620063074/#c458606877322824034

game developers do nearly nothing in term of support for Crossfire and SLI
(at max they need properly detect GPU memory available as it's not shared)
everything else is left to IHV's drivers ... in future this might be in hands of DX12+ / Vulkan

Any comments on this? Are the devs that lazy to not offer proper detection for the vRAM in games where this technology isn't usable? Are AMD and nVIDIA that lazy/indifferent to offer support in drivers or the above is just standard PR talk?

 

[Rroff]

Its a common fallacy that game developers need to program in multi GPU support - ostensibly game developers can do absolutely nothing (including any memory detection) and multi GPU would work - it would be better looked at as a game having multi GPU compatibility than multi GPU support. (This ostensibly will change to a certain extent with DX12 where developers will have a bit more direct say in how their program is using the GPU(s)).

The problem gets more complicated when developers use non-standard techniques to implement features - this might be due to an innovative or cutting edge feature or out of the box thinking but equally can be down to lazy development where they do just enough to make the feature work in their game and then move on to the next bit of the project rather than fully implement said feature to standard. Standard use of OpenGL/DX features usually = multi GPU compatibility, non-standard use often means that multi GPU is broken unless the developer specifically tests against it and makes changes as appropriate to retain multi GPU compatibility.

Things get very complicated when games use features (even standard ones) that require information from previous frames and/or data that would require it to be fetched from the other GPU to the currently active one and require the developers to put a lot of thought into their implementation to minimise these kind of issues or sometimes, especially for some post processing effects, it simply isn't possible to implement them and keep multi GPU compatibility or atleast not without subsequent work AMD/nVidia to implement driver level workarounds.

 

[VincentHanna]

Bohemia Interactive, whose games (ARMA series) are all massively CPU bound.