Nvidia's SLI Technology In 2015: What You Need To Know

[endeavour37a]

Quote:
"In part two of this series, we'll look at the red team's rival multi-GPU technology called CrossFire (we've already lined up a couple of AMD's next-gen cards to make this one happen for you)."

Does this mean R9 3xx cards?

Yes.

Thanks for the heads up on this, that will be great to get a look at the new AMD card performance. Perhaps you could say which ones you will be testing? Considering that you used top shelf NV cards like the 980s would they maybe be the R9 380x cards?

I understand they are reworked Hawaiian cores from the 290/290x cards, they say renamed Grenada. If so then your test results would be pretty relevant to everyone running 290/290x cards now.

 

[Evarin]

Great article. I'm very much looking to center my next build around VR, so addressing SLI from that perspective was quite useful.

For now, the plan is likely to buy 1 980 ti and possibly get a second if it proves beneficial to VR gaming.

 

[Evarin]

Great article. I'm very much looking to center my next build around VR, so addressing SLI from that perspective was quite useful.

For now, the plan is likely to buy 1 980 ti and possibly get a second if it proves beneficial to VR gaming.

 

[baracubra]

Can anyone tell me what kind of bottleneck I would get from my CPU (i5 4670K) if I was to get a second 780Ti? ...and is my MSi reference card compatible with EVGA ref. cards (the normal ones, not the SC or above)?
Thx.

While I'll leave the bottleneck question to someone with a bit more information on the matter. Previously they have been compatible, but as of late I've heard that issues do sometimes crop up

 

[10tacle]

Excellent article! I was one of those early SLI adopters with a pair of Voodoo2 cards. However when the TNT2 came out, I switched to back to Nvidia being an owner of the original TNT and Riva 128 cards and have gone between high level single GPUs and mid-range SLI GPUs ever since.

I'm running a pair of EVGA Superclocked 970s with an i5 4690K running at 4.7GHz. They do fine for a 1440p monitor overclocked to 90Hz. Never had any micro-stuttering issues and most games are locked at V-sync. However, I would much prefer to have a single GPU solution again even if it costs more for the same performance. The amount of heat those cards pump out the back of my case is the most I've ever experienced, and that's even with them being throttled back by a 90fps cap. Unfortunately, Nvidia has pushed back the 980 Ti release into 2016 and these 970s will be worth half what they are now next year on the used market. No plans to move to 4K any time soon for gaming having just moved up to 1440p less than two years ago.

 

[RedJaron]

The motherboard details in section 2 aren't complete. First, not all LGA1150 boards with two x16 length slots can handle PCIe lane splitting to accommodate SLI or CFX. Only Z chipsets can split lanes to do this.

Second, regardless whether it's a Z chipset or not, many boards have a second x16 length slot that's only wired for 4 lanes. In order to run SLI on LGA1150, you need a Z chipset with at least two x8 wired slots. Generally, if your mboard doesn't come with an SLI bridge in the box, it doesn't support SLI.

Third, you didn't mention anything about AMD boards here. The slots and lane wiring requirements will be the same as LGA1150, but you need a 990 chipset for AM3+. The only FM2+ boards that have the necessary lane support are the A88X chips, but they don't seem to "officially" support SLI.

 

[mechan]

Thanks for the heads up on this, that will be great to get a look at the new AMD card performance. Perhaps you could say which ones you will be testing? Considering that you used top shelf NV cards like the 980s would they maybe be the R9 380x cards?

I understand they are reworked Hawaiian cores from the 290/290x cards, they say renamed Grenada. If so then your test results would be pretty relevant to everyone running 290/290x cards now.

Gigabyte has agreed to loan us two of the new AMD flagship cards upon launch. That's all I can say.

Filippo

 

[mechan]

I feel like it would be beneficial to clarify on the statement that "you really need two *identical* cards to run in SLI."

While true from a certain perspective, it should be clarified that you need 2 of the same number designation. As in two 980's or two 970's. I fear that new system builders will hold off from going SLI because they can't find the same *brand* of card or think they can't mix an OC 970 with a stock 970 (you can, but they will perform at the lower card's level).

PS. I run two 670's just fine (one stock EVGA and one OC Zotac)

What you say -was- true with 6xx class cards. With 9xx class cards, requirements for the cards to be identical have become much more stringent!

Not true. According to Nvidia's FAQ page:

"Can I mix and match graphics cards from different manufacturers?
Using 180 or later graphics drivers, NVIDIA graphics cards from different manufacturers can be used together in an SLI configuration. For example, a GeForce XXXGT from manufacturer ABC can be matched with a GeForce XXXGT from manufacturer XYZ.

Can I mix and match graphics cards if one of them is overclocked by the manufacturer?
Yes. A GeForce XXXX GTX that is overclocked can be mixed with a standard clocked GeForce XXXX GTX."

http://www.geforce.com/hardware/technology/sli/faq#c17

The 180 driver release is a 2008 branch (i.e., 7 years old.) I believe that FAQ information to also be outdated. We've had consistent issues in our labs getting 9x0s from different manufacturers working with each other.

Filippo

 

[Gunbuster]

"A motherboard with at least two free PCIe x16 slots, operating in at least in x8 mode (Nvidia does not support SLI on x4 links). Pretty much all LGA 2011, LGA 2011-v3 and LGA 1150 motherboards satisfy this requirement."

Since when? As far as I know the motherboard MUST be SLI certified by Nvidia. AKA the Nvidia driver looks for a BIOS flag that says SLI is OK. No nvidia SLI logo no SLI for you! http://www.geforce.com/hardware/technology/sli/motherboards

 

[chechak]

1080p gives a great deal for gamer's now a days ...

 

[TallestJon96]

Great article and good analysis, but I have to disagree with your conclusion. Some games don't work with SLI for months, others have glitches, and scaling is usually between 60%-80%. The only time I would consider SLI is for 4k, but when games don't launch with SLI support, then you cannot reliably game at 4k.

I know toms had an article about AMD and NVIDIA being SLI compatible, and by extension different cards for the same manufacturer (say a gtx 970 and 680) would be compatible. This would make SLI mug more viable, as you can keep 1 old graphics card and buy a new one, and always have your last graphics card and newest one working together.

 

[Eggz]

Sounds like a "Don't do it unless you need to, but it's worth it if you need it" situation. I'd vote for that!

 

[endeavour37a]

Thank you Filippo (mechan) for the info, from what I hear they will be released in June sometime.

Quote:
"I know toms had an article about AMD and NVIDIA being SLI compatible, and by extension different cards for the same manufacturer (say a gtx 970 and 680) would be compatible."

TallestJon96, you cannot SLI a 970 and 680 together, one is a GM204-200 and the other a GK104-400. You can XFire some AMD cards with different cores, I saw the list from AMD a bit ago, but not NV cores.

So NV pushed back the 980Ti to 2016, they were going to get it out by the end of summer, dang it! I thought they were just holding it back waiting for AMD's new cards, not like they have to engineer it as it's just a Titian X w/6GB in-stood of 12GB.

 

[gallovfc]

I have no problem using DSR while playing games like GTA 5, WoW, Laft 4 Dead 2. The only problem is if you ALT+TAB some games may come back to 1080p when you return to it.

 

[gallovfc]

Btw I'm using a Core i5 4690k and GTx 970 SLI on Windows 8.1...

 

[BradleyJames]

I too really wished they released a 4 gb 780ti. im running 2 in sli and they are great cards. i was not impressed with the mere 5% ( if that ) performance increase of the gtx 980.

 

[Eggz]

I too really wished they released a 4 gb 780ti. im running 2 in sli and they are great cards. i was not impressed with the mere 5% ( if that ) performance increase of the gtx 980.

Yeah, I have that card too. It's got more horsepower than the VRAM can handle. Sad :-/

 

[Wisecracker]

Thanks for the article.
I'll note as others have ... planning for, or counting on a multi-GPU rig is not always in your best interest. By the time you are ready for that second card most likely there will be a single card on the market that will come close (or exceed) the performance of your multi-GPU setup.

And, while a comparison with Crossfire scaling will be greatly anticipated by many -especially with the new Radeons- the 'scaling comparison' seems a bit premature as the Catalyst drivers are likely to be less than 'mature' (understanding that the Volcanic Islands refresh is quite an unknown commodity at this moment).

Years ago --- THG did a comparison of 'early' Crossfire driver performance on a new card(s) versus subsequent updates, and IIRC, there was quite a nice boost.

Including 'mature' R9 290/X Crossfire scaling with that of the new varieties of 'green' Radeons would seem to be appropriate (not knowing , of course, if AMD will open the door to 200-series Hawaii running in tandem with a new 300-series Hawaii 'refresh')

 

[legokangpalla]

I still prefer crossfire as it has the sfr supertiling option. Afr is unplayable due to microstuttring except for few optimized games.

 

[mapesdhs]

Filippo,

S'funny, you have the same EVGAs I bought, which I chose precisely because
of the 980 behaving so well for Elite Dangerous. Coupla things though...

"...or an even more expensive LGA 2011-v3 platform if you want to go
beyond two-way SLI."

Nah, just buy a used X79 board, much cheaper! I bought a P9X79 Deluxe for
75 UKP (for my brother), and a Rampage IV Extreme for 113 UKP, beat that.
Bought another R4E for 103 for benching with a 4820K.

A couple of points about Elite Dangerous: a single 980 does indeed give
very high frame rates, but what I wanted was to be able to crank up the
detail as much as possible while always staying above 60fps. A single
980 achieves this nicely, with just one of the detail settings being one
level below max. Also, ED performance reviews showed that having a
strong main CPU can definitely help when there's a lot of onscreen
action, hence why I went with a used X79 build (3930K @ 4.8) instead
of a new Z97, which was much cheaper too. And when I eventually get
a 4K TV, the mbd will handle another in SLI just fine with no worries
about PCE/bw limitations, etc.

Interesting to compare your stock SLI score against mine with 2x 980 @ stock:

http://www.3dmark.com/compare/fs/4058701/fs/3974252

Alas it shows that even Firestrike is now susceptible to distorted overall scores
because of a strong CPU, even though the Graphics Test numbers are not that
different (fair bit better for the Combined Test though of course).

Ian.

PS. Firestrike fun with 3-way:

http://www.3dmark.com/fs/3971612

and about the quickest P55 system you can have, hehe... (runs surprisingly
well with an i7 870, GFX Test 2 is only 3% slower on the P55, while GFX Test 1
only loses about 10%):

http://www.3dmark.com/fs/4099529

 

[mechan]

Nah, just buy a used X79 board, much cheaper! I bought a P9X79 Deluxe for
75 UKP (for my brother), and a Rampage IV Extreme for 113 UKP, beat that.
Bought another R4E for 103 for benching with a 4820K.

I am a big fan of creative solutions myself - hard to recommend used boards to a general audience though. That being said, I have myself an old Core i7-950 which works perfectly fine for pretty much anything I through at it.

Interesting to compare your stock SLI score against mine with 2x 980 @ stock:
http://www.3dmark.com/compare/fs/4058701/fs/3974252
Alas it shows that even Firestrike is now susceptible to distorted overall scores
because of a strong CPU, even though the Graphics Test numbers are not that
different (fair bit better for the Combined Test though of course).

That's why I haven't used numerical scores in the review. CPU and combined scores of Firestrike have always been pretty much meaningless from a real-world-performance perspective, and especially so when looking at GPUs.

Filippo

 

[mapesdhs]

I am a big fan of creative solutions myself - hard to recommend used boards to a general audience though.

There's a lot of utility in used parts IMO, and of course I would always suggest
only buying from reputable sources, sellers that accept returns, etc. Btw, not
just used, but also new sold via normal auction or even just bargain BIN amounts,
eg. sorting out a budget system for a friend atm, I bought a new Intel 520 240GB
for 45 UKP, a new Antec 300 case for an astonishing 17 UKP (that includes shipping!
Seller accepted an offer of just 10), used Z68 mbd for 41 from a good refurb seller
(novatech). A while ago I bagged a completely new ASUS M4E for only 80.

However, I understand what you mean, it's not for everyone, and by definition
not everyone could or would want to. Given the nature of the audience here
though, it's worth mentioning, especially since sometimes supplies of good stuff
in qty can be surprising. ASUS inparticular chucks out a lot of refurb boards
with warranties, or at least they do in the UK.

That being said, I have myself an old Core i7-950 which works perfectly fine for pretty much anything I through at it.

I'd like to get hold of a 950, a more applicable X58 example than the X5570
I have atm.

That's why I haven't used numerical scores in the review. CPU and combined scores of Firestrike have always been pretty much meaningless from a real-world-performance perspective, and especially so when looking at GPUs.

Indeed, but now it's getting kinda worse just like 3DMark06 eventually became.
I suppose they could change the weightings, but of course that would invalidate
older scores. Pairing GPUs with ever more powerful CPUs means the main GFX
tests become less relevant when wrapped up in the overall score.

Ian.

 

[KaiserPhantasma]

and I thought I was going to read an informative post about what nvidia has in their sleeves for 2015

 

[Deyadissa]

People are running into lots of problems with the SLI in 900's series with two different brand cards. I do not recommenced getting 2 different brands of the same card, it would have saved me at least 10 hours of my life troubleshooting.

 

[Eggz]

FOLLOW UP QUESTION FOR TOM'S

RE: SLI Bridge Bandwidth - Will Tom's think of, execute, and publish results of tests showing whether the very low bandwidth of the SLI Bridge poses a bottleneck? I have a strong feeling it does. The connectors are one of the few pieces (if not the only piece) in high-performance systems that rely on technology more than a decade old, and perhaps it's nearly two decades old.

SLI BRIDGE

What is the function of the SLI connector?
. . The SLI connector enables inter-GPU communication of up to 1GB/s, consuming no bandwidth over the PCI Express bus.

But look at how long Nvidia's been using this.

Manufacturer: NVIDIA
Type: Multi-GPU
Release date: 2004
Predecessor: Scan-Line Interleave

PCI-e first came out the same year (2004) with PCI-e 1.0, and the max bandwidth of a x 16 slot was only 4 GB/s. So the SLI Bridge provided up to a 25% increase. Okay. But now the PCI-e slots have quadruple the bandwidth, with roughly 16 GB/s for PCIe- 3.0 x 16.

PCI Express link performance
PCI-e version ----- Line code ----- Transfer rate ----- Bandwidth Per lane ---------- In a ×16 (16-lane) slot

1.0 ------------------- 8b/10b ---------- 2.5 GT/s ------- 2 Gbit/s (250 MB/s) --------- 32 Gbit/s (4 GB/s)
2.0 ------------------- 8b/10b ---------- 5 GT/s --------- 4 Gbit/s (500 MB/s) --------- 64 Gbit/s (8 GB/s)
3.0 ------------------- 128b/130b ----- 8 GT/s --------- 7.877 Gbit/s (984.6 MB/s) - 126.032 Gbit/s (15.754 GB/s

The cable itself may actually be much older than 11 years. Today's SLI bridge may in fact use the same cable configuration that 3Dfx used (and 3Dfx started SLI) starting back in 1998.

SLI from 3dfx was introduced in 1998 and used in the Voodoo2 line of graphics accelerators.

If current SLI Bridges are just prettier versions of the original SLI cables, that would make the modern SLI bridge a 17 year old interface on cards like the Titan X! After researching without finding definitive information, it certainly does appear that the 3Dfx SLI cable and the Nvidia SLI Bridge could differ only by appearance.

Regardless of the age, however, the fact remains that modern SLI bridges are limited to a measly 1GB/s. That was originally to spare PCI bandwidth, but we've moved on to PCI-e, which is much faster. We have plenty of good information showing that PCI-e 3.0 provides excessive bandwidth for GPUs beyond x 8 (click image below for link).


If PCI-e 3.0 x 8 is enough for even the fastest cards, then x 16 (with twice the bandwidth) is WAY more than enough. So why, then, would it make sense to use an SLI Bridge when the PCI-e bus has potential to do a far better job?

Perhaps the Nvidia purchase agreement used to acquire 3Dfx has a condition that requires the connector technology to stick around. Maybe there's not enough of an SLI market for Nvidia to allocate R&D toward the issue. And maybe 1 GB/s is actually plenty of bandwidth given the current state of things. Who knows.

The only clear thing to me on this topic is that the SLI Bridge seems to clearly not fit. If possible, it should be updated. And if not possible for some reason, there should be information telling people when the issue preventing innovation will expire.