Question Crossfire RX 570

[clorotan7]

I've never been able to see how crossfire works, like, is there something similiar to nvlink that connects them?
If i buy 2x 4gb rx 570, does that make it 8gb?

 

[Metal Messiah.]

You might sometimes need a crossfire bridge, depending on the GPU. Also, the motherboard must be AMD CrossFire certified with at least two PCIe x16 slots available, running at a minimum of PCIe x8 speed.

BUT, only older AMD cards needed a crossfire bridge. From the 200 series up (including the 3xx) you don't need a bridge anymore, and you can do it over the PCIe bus, IMO. Most 280x series or older still require a crossfire bridge connection. However, the 290 and 290x series and above cards have bridge-less crossfire support.

 

[Metal Messiah.]

If i buy 2x 4gb rx 570, does that make it 8gb?

Oh, BTW. No, I don't think the VRAM is going to get stacked. Each GPU will still use it's own Frame Buffer which is 4GB. You can't get 8GB by combing those two cards in CFX mode. I think the same applies to SLI as well.

Because in order for VRAM to stack, we need to use Split Frame rendering/SFR, in Crossfire or SLI Mode. So 4GB+4GB is still 4GB. Most of today's multi-GPU setups use "Alternate frame rendering/AFR". Though, "MANTLE API" does support VRAM stacking, but the DEVs need to implement this in games.

In AFR, each GPU renders each of the other frame (either the alternate Odd or Even).
In SFR, each GPU renders half of every frame. (top/bottom, or plane division).

For example. Civilization V, a mantle Game supports SFR. This whole VRAM stacking will all depend on the drivers though, as well as the Game developers to implement it, especially in DX12. Btw, only very few games like the "Ashes of the Singularity/AOTS" actually supports this DX12 m-GPU setup. AOTS was coded by the developers to take advantage of DirectX 12's functionality, also allowing "cross-branded" video cards to be paired as well !!

AOTS is one of the games that supports this form of explicit multi-GPU with DX12. Apart from that, very few game titles are going to benefit from this feature.

On some Off Topic note, Nvidia's NVLINK might be some other story.

I think the main advantage of Nvlink is that it might help with peer-to-peer interface, VRAM stacking, because essentially the GPUs are much closer together now, also bringing the latency of a GPU-to-GPU transfer way down. So unlike SLI, where the latency had to go through PCIe as well as memory, Nvlink behaves in a different manner. We can think of it as an app that looks at one GPU, and then looks at another GPU and does something else same time. So it seems NVlink will be the future when it comes to multi-GPU setup, but sadly ONLY on the high-end market segment, as other Turing cards will lack NVLINK support.

 

[DSzymborski]

Correct, VRAM doesn't stack. Imagine it takes you three hours to drive to the beach by yourself. If your friend comes along for the ride, it still takes three hours; the VRAM is mirrored.

 

[lux1109]

I wish we could get double the gpu memory by linking any two GPU models....Btw, Cfx and SLI are both a hassle these days. Always go for a single gpu instead.

 

[Metal Messiah.]

Btw, Cfx and SLI are both a hassle these days. Always go for a single gpu instead

Agree on that part though. Not many games scale well on SLI/CFX. I always recommend going for a SINGLE powerful GPU. For example, Wolfenstein the New Order has the worst support for SLI. That even NVidia's own driver recommended setting is to force single GPU, and that is the worst possible case scenario.

Also, some games do not even benefit from either CFX/SLI, despite they having full support for it. Little to no performance impact, but there are few PC titles which do scale well.

 

[renz496]

I've never been able to see how crossfire works, like, is there something similiar to nvlink that connects them?

in the past the two cards in CF are connected by CF bridge. it is almost similar to the way nvidia SLI (pre turing) being done. but starting from GCN second generation AMD ditch the bridge and rely 100% on the PCI-E slot to "connect" both card.

If i buy 2x 4gb rx 570, does that make it 8gb?

no. in CF each card will needs it's own pool of VRAM so the system will still going to see the system to have 4GB VRAM. in general you can assume it like this (using RX 570 as example):

RX 570 4GB + RX 570 4GB = 4GB
RX 570 4GB + RX 570 8GB = 4GB (meaning the game can only access 4GB of your VRAM. the extra VRAM on the second card will be inaccessible to the game due CF limitation)

Because in order for VRAM to stack, we need to use Split Frame rendering/SFR, in Crossfire or SLI Mode. So 4GB+4GB is still 4GB. Most of today's multi-GPU setups use "Alternate frame rendering/AFR". Though, "MANTLE API" does support VRAM stacking, but the DEVs need to implement this in games.

to my knowledge even SFR can't really make the VRAM stacking happen. if that was possible then we should see how it is done a long time ago even in limited demo scenario. AMD once claim it is possible to combine the VRAM using though low level API but they never show us how it is done. not even a simple demo to prove it. nvidia was the first to make VRAM stacking possible for multi GPU use. but they able to do it by using their proprietary NVLink connection. meaning there is specific hardware to make it possible.

For example, Wolfenstein the New Order has the worst support for SLI. That even NVidia's own driver recommended setting is to force single GPU, and that is the worst possible case scenario.

for as long as i can remember the Id Tech engine are not multi GPU friendly even the old one. personally i will advice anyone to avoid multi GPU setup. if you want real performance increase get faster GPU. the state of multi GPU is not as it were a few years ago. and it is sad to see how VRAM stacking finally becoming a reality

 

[TechyInAZ]

Yeah vram isn't stackable.

This is because of how Crossfire works:

One GPU processes one frame and the other GPU processes the next frame.

GPU 1 = Frames 1,3,5,7,9,11,13 etc
GPU 2 = Frames 2,4,6,8,10,12,14 etc.

So one processes all the even frames and one the odd.

But, technically you can make it where two 4GB GPUs = a full 8GB of vram.

This is done with another type of image rendering where GPU 1 & 2 process the SAME frame. But are split in half, so one GPU will render half of a frame and the other GPU will render the other half.

But this technique almost never sees the day of light because it is more complex to run than the more traditional method.

Either way, I suggest you not run CrossfireX. mutli GPU support for games has seen a very steep decline over the past few years. CrossfireX is typically far worse due to bad driver support vs SLI too.

 

[lux1109]

For example, Wolfenstein the New Order has the worst support for SLI.

Agree on that. I've tired playing the game on a single gpu, it was fine. No performance issues. A friend of mine is using an SLI setup, and the game performed worse on his system, lol. It's a boring game btw.

 

[david_the_guy]

I used to have a crossfirex setup. That didn't help much with all the games which I palyed, so I had to sell one of the GPUs. Buy a single card which is having more vram. That's my advice as well.

 

[geofelt]

You may win synthetic fps benchmarks with dual cards, but yur game play will be better witn a single good card.
dual gpu is prone to stuttering and screen tearing.
Many games do not support dual gpu at all.

 

[david_the_guy]

Yup, running some synthetic benchmarks on a dual card setup might help increase the score, but not in games.

Btw, only very few games like the "Ashes of the Singularity/AOTS" actually supports this DX12 m-GPU setup. AOTS was coded by the developers to take advantage of DirectX 12's functionality, also allowing "cross-branded" video cards to be paired as well !!

Are you talking about the strategy game title from oxide games/stardock ?

 

[Metal Messiah.]

Are you talking about the strategy game title from oxide games/stardock ?

YES.

 

[ElectrO_90]

I've never been able to see how crossfire works, like, is there something similiar to nvlink that connects them?
If i buy 2x 4gb rx 570, does that make it 8gb?

If you look at reviews about how much memory is used in games (Guru3d) then you see most games even now, at 1080p don't utilise 4GB let alone 8GB

 

[david_the_guy]

YES.

Okay got it. Ive read about that AOTS title, and it's multi gpu scaling and performance. The devs did a pretty good job with this title. sadly, it's not my type of game. I don't like real time strategy. But it's good witnessing how tech has advanced since past few years. I hope more games take advantage of this feature.

 

[DSzymborski]

Okay got it. Ive read about that AOTS title, and it's multi gpu scaling and performance. The devs did a pretty good job with this title. sadly, it's not my type of game. I don't like real time strategy. But it's good witnessing how tech has advanced since past few years. I hope more games take advantage of this feature.

It's been awhile since AOTS came out and if anything, SLI/CF support has gotten worse since then, not better. It was always a pain for the Nvidia/AMD because of the driver support necessary and their reward for all the trouble was large people buying second cheaper cards for SLI/CF instead of a single, more expensive card when their old GPU got too slow. Considering how few people used multi-GPU solutions anyway, the effort/benefit ratio is pretty dreadful. The GPU manufacturers don't like SLI/CF, the game studios rather focus on other things, and consumers are largely uninterested, which is why you've seen the support wither away.

 

[david_the_guy]

It's been awhile since AOTS came out and if anything, SLI/CF support has gotten worse since then, not better. It was always a pain for the Nvidia/AMD because of the driver support necessary and their reward for all the trouble was large people buying second cheaper cards for SLI/CF instead of a single, more expensive card when their old GPU got too slow. Considering how few people used multi-GPU solutions anyway, the effort/benefit ratio is pretty dreadful. The GPU manufacturers don't like SLI/CF, the game studios rather focus on other things, and consumers are largely uninterested, which is why you've seen the support wither away.

Ok. Thanks for the info. Appreciate it.

 

[renz496]

The GPU manufacturers don't like SLI/CF, the game studios rather focus on other things, and consumers are largely uninterested, which is why you've seen the support wither away.

to me it's not like GPU maker does not like it but rather after pushing it so hard for years the percentage of PC gamer opt for such setup still very small. not to mention there is a lot of resource dedicate just to make it works in many tittles since our games are not designed to take advantage more than one GPU automatically unlike how it was with multi core CPU. an ex nvidia engineer said that more than half of driver team effort was to make SLI work in existing games. that's a lot of resource dedicated just to satisfy very small group of PC gamer.

though i heard some rumor that intel want to introduce some interesting multi GPU tech. one that does not need profiles like current CF/SLI and games will automatically recognize several GPU inside the system as one "big" GPU. meaning it just work in any existing games without the need specific software.

 

[lux1109]

an ex nvidia engineer said that more than half of driver team effort was to make SLI work in existing games. that's a lot of resource dedicated just to satisfy very small group of PC gamer.

That's true. A lot of resources/time/effort are also required.

 

[david_the_guy]

what abut the upcoming navi cards ? I think Amd should drop full support for crossfire on navi as well, because it doesn't provide much benefit..

 

[davew1860]

Like others have mentioned, I would avoid Crossfire and just go with a single video card. The price to performance ratio is much smaller/better that way.

For about the same price as two RX 570 4GB's, you could get one RX Vega 56 8GB. It's a strong card.

 

[lux1109]

For about the same price as two RX 570 4GB's, you could get one RX Vega 56 8GB. It's a strong card.

VEGA is getting a bit old. The new RX 5000 Navi GPU is coming out soon though. AMD just made an announcement. It will rival the RTX2070.

 

[david_the_guy]

VEGA is getting a bit old. The new RX 5000 Navi GPU is coming out soon though. AMD just made an announcement. It will rival the RTX2070.

fyi, it's only going to be on par. it won't beat teh rtx with a huge margin though.

 

[lux1109]

Will the rx 5700 NAVI also support CFX ?

 

[david_the_guy]

what abut the upcoming navi cards ? I think Amd should drop full support for crossfire on navi as well, because it doesn't provide much benefit..

To quote my own comment, I was just reading a REDDIT and someone came up with an answer stating than these new cards are most probably not going to fully support CFX., and also AMD might also release a DUAL GPU as a solution.