AMD VR Performance

0h_no_not_again · 10 Oct 2016 at 08:48

Hi All,

I'm trying to figure out how and why AMD cards are showing such sporadic VR performance, ranging from OK to shocking. I'm basing this on personal experience with an R9 290X and HardOCP's benchmarks: http://www.hardocp.com/reviews/vr/

There are two major game engines running 99% of VR content: Unity and UE4

As a huge generalisation, it appears that Unity is getting OK performance on AMD cards, where UE4 is pretty terrible. By OK performance I mean close to but behind NVidia at all price points. Obviously we can live with the Unity performance, but UE4 is unplayable.

Now as far as I can figure, there are two reasons for this happening:
1. AMD haven't worked with UE4 (at all) to get their hardware playing nice.
2. UE4 has adopted vendor specific toolsets that are gimping AMD hardware

Does anyone have some insight on the cause(s)?
Is AMD doing anything to rectify the situation?
I'm quite positive about DX12 integration into these engines, as it might give AMD hardware a decent boost, but when is it coming?

Anyway, any insight is appreciated. Googling didn't turn up much except for the repetition of "LiquidVR" as a buzzword...

Asa · 10 Oct 2016 at 12:11

Ah man, this is the worst thing I've read today. I was so close to pulling the trigger of a Rift, but it looks like the price just went up significantly

0h_no_not_again · 10 Oct 2016 at 12:21

Asa said:
Ah man, this is the worst thing I've read today. I was so close to pulling the trigger of a Rift, but it looks like the price just went up significantly

Ah sorry. I was hoping it wouldn't put anyone off...

At least there are people doing VR Benchmarks now so you don't go in blind. I'm not a huge Kyle from HardOCP fan, but his approach and data looks pretty solid.

ArmitageShanks · 10 Oct 2016 at 13:06

Have nVidia myself, but as far as I can tell the VR performance enhancements have gone completely unused. UE4 doesn't make use of multi-GPU configs either, so that's no good. And DirectX 12 performance is terrible on nVidia hardware compared to AMD

Not looking good for the future...

Asa · 10 Oct 2016 at 13:33

0h_no_not_again said:
Ah sorry. I was hoping it wouldn't put anyone off...

At least there are people doing VR Benchmarks now so you don't go in blind. I'm not a huge Kyle from HardOCP fan, but his approach and data looks pretty solid.

Better to find out now than after I've dropped the cash on it, so thanks. I was going to stick in on a rig with an R9-295X, so effectively the same as you (as I gather crossfire doesn't work?). It's perfectly timed feedback.

Unfortunately it doesn't just add the price of a new GPU, it also adds complication because that PC has a freesync monitor so I'd soft-locked myself into AMD.

I hear that Playstation VR is comfortable :|

mid_gen · 10 Oct 2016 at 14:19

UE4 used a deferred renderer, whereas Unity's default is a forward renderer.

Deferred rendering takes multiple passes on the frame and enables you to use more dynamic lighting setups and fancier post-processing and temporal stuff like TAA (hence no SLI support).

There's a UE4 branch with a forward renderer designed for VR use (I think nVidia made it?)....rumours it'll be incorporated into the main engine soon.

SLI/Crossfire is a big nope for VR anyway, too much latency.

0h_no_not_again · 10 Oct 2016 at 14:36

I've heard rumours that LiquidVR enables Split Frame Rendering for Crossfire (one GPU per eye?). Significant googling turned up terrible anecdotal evidence to back it up...

mid_gen · 10 Oct 2016 at 15:06

Yeah SLI Crossfire is a nope with the usual alternate frame rendering method. Better parallelisatiom with DX12 might solve it but I don't think anything is readily available atm.

SKILL · 10 Oct 2016 at 17:26

Both AMD and nvidia have advertised the ability to do 'one gpu per eye' in crossfire/sli setups, but both require game specific support and hence are, afaik, completely unused which is a bit of a shame...