Will a Core i7 7700K bottleneck two GTX 1080's in SLI?

Fixadent · Dec 22, 2016

Will a Core i7 7700K bottleneck two-way SLI GeForce GTX 1080's? Or do I need a 6-8 core processor?

Herc08 · Dec 22, 2016

You could get two 1080s with a i7-6700 just fine, so the 7700 should be fine too. How many displays are you planning to use? Why not just get a GTX Titan instead of two 1080s?

Eximo · Dec 22, 2016

Pair of 1080s is a lot more GPU than even a Titan X. 40 SM units (5120 cores) vs 28 on the Titan. Only lose out on the 12GB and the bandwidth.

Herc08 · Dec 22, 2016

Eximo :

Is that for the Pascal version or the Maxwell version?

Ecky · Dec 22, 2016

The answer is yes, no, maybe, and sometimes, because CPU and GPU load are largely unrelated. If you're aiming for 144hz gaming, no CPU will get you to 144fps in every game but in the vast majority a modern i7 will get there. If you're going to be running 60hz screens (let's say 3x 4K 60hz screens) even a Core i3 is enough for 60fps in most games, though an i5 would be a safer bet.

The amount of GPU power you have is irrelevant to bottlenecks. You need to buy enough CPU power to hit the framerates you want in the games you play. You can always get there with a GPU by lowering the graphical settings, more expensive GPUs just let you run higher graphical settings.

Eximo · Dec 22, 2016

Herc08 :

Pascal.

Maxwell Titan X has 24 SM units as compared to the 980's 16. 980Ti has 22 SM units. Though the Titan X Maxwell had 12GB of memory compared to the 4GB on the 980, so a significant difference. 8GB to 12GB, not so much. And the 1080 Ti is going to have the same 12GB. Interested in seeing the price.

Herc08 · Dec 22, 2016

Eximo :

Well if you are saying the SLI is more efficient to than the Titan X, then go with that. The downfall is having the PSU contribute more power to handle both GPUs. It will interesting to see wha tthe 1080 Ti can do.

To the OP: There should be no bottle neck.

Eximo · Dec 22, 2016

I would not use the word efficient. More powerful, yes. Cost effective, maybe. Though that does mean a high bandwidth SLI bridge and a power supply capable of running two GPUs, an SLI capable board, and a case to accommodate, plus the costs of whatever cooling is involved.

I intentionally went from a pair of 980 to a single 1080. The writing is on the wall. SLI support is going to be on a title by title basis until the majority of games are supporting multi-gpu on DX12.

Supernova1138 · Dec 22, 2016

Eximo :

Which will also be on a title by title basis as the developer is required to support it, and I believe developers would need to do even more work on their end compared to how it is now as DX12 is a lower level implementation that requires the developers to deal with stuff that previously would have been handled at the GPU driver level.

I'd expect multi-GPU support to get even worse unless the consoles start offering external modules with a second GPU as an upgrade option. As it stands now only 1-2% of the already small (relative to consoles) PC audience has an SLI or Crossfire setup. Developers probably don't want to spend lots of extra money to support a feature that only a small subset of the audience can use. I could see multi-GPU becoming somewhat like GPU accelerated PhysX, where it only gets supported when Nvidia or AMD pony up some cash to the developer to get them to include it.

Fixadent · Dec 23, 2016

Is a 1,000W PSU enough for two GTX 1080's in SLI?

Herc08 · Dec 23, 2016

Fixadent :

It should be more than enough.

Ecky · Dec 23, 2016

The 1080 has a 180w TDP. Paired with a 91w CPU and assuming the rest of the system is (conservatively) 50w, you're at almost 500w even. It's a good idea to have a bit of extra power to spare, so I'd say a 750w unit would be appropriate for running the system at stock or with a mild OC.

Unsolved · Apr 4, 2017

Herc08 :

Unsolved · Apr 4, 2017

beacuse 2x 1080's is 500 dollers or euro or what ever cheaper and it gives you a extra 10 to 30 fps more depends on what game u play

BaysideLukaz · Apr 19, 2017

I've heard talk of pcie lanes on cpu's. Does this mean that you would benefit from getting a cpu with, let's just say "2x pcie x16 lanes" in order to fully utilize 2 GTX 1080's? And would I be able to run an ssd in the other pcie lanes on my motherboard?

I am currently running a liquid cooled fx9590, on a sabertooth 990fx r.2.0 Motherboard with a single GTX 1070. Corsair vengence 4x4gb 1600 mhz RAM.
I will soon rebuild to a liquid cooled i7 7700k on a ASUS Z270 Maximus formula IX Motherboard. GSkill Trident Z 2x8 gb 3000 mhz ram.
I plan on upgrading to 2x GTX1070 sli config. or single 1080, then some time in the future 2x 1080 sli confg.

Hence the question about cpu pcie lanes.... I just found that the I7 7700k has up to 1x16, 2x8, 1x8+2x4.

Eximo · Apr 19, 2017

The CPU itself offers 16x lanes directly to two x16 slots, so 16x/0x, 8x/8x, and the rarer 8x/4x/4x (For three way crossfire)

The Z270 PCH offers its own 28 lanes? Or 24?, either way plenty of lanes for your PCIe SSD and other PCIe lane consuming devices.

Ryzen CPUs offer a similar platform of 16x direct to CPU lanes.

Intel's X99 platform offers more with the right CPU. 28 Direct CPU lanes or 40 Direct CPU lanes, the X99 PCH offers an additional 8x PCIe 2.0 lanes if I recall.

I would not recommend the intermediate step of 1070 to 1080. Go ahead with the 1070 SLI or replace the 1070 with a 1080Ti (or better) at a later date. 1070 SLI is more powerful, but then you have to deal with SLI.

BaysideLukaz · Apr 19, 2017

Thank you for a good answer! I appreciate the advice and will definitely make a point to remember that when the time comes.

8x/8x??? The that's where i scratch my head while thinking "don't I want 16x/16x?" Wouldn't 8x/8x leave you me with half the bandwidth for each card?

Really clean build you have there! Good work!

Eximo · Apr 20, 2017

Yes, less available bandwidth per card. I would have to track it down, but someone showed only a benefit when running very high resolutions, otherwise the FPS loss when running something like a GTX1080 in 8x mode was only a percent or two. Having two cards in that scenario is going to be quicker regardless. Just that SLI and Crossfire are going to be completely up to the developers going forward in DX12, or linked and unlinked (non-matching cards) mode multi-GPU.

You can get 16x/16x with a i7-5930k+ or i7-6850k+, but that would only be needed if you were wanting to run 3440x1440@75-100Hz, or 4K or something like 5760x1080. But even if not it wouldn't be too big a deal.

Odd you should mention my build, ordered a few things and will be putting a few finishing touches in tomorrow. (White PSU cables) Just updated the BIOS and had to re-overclock the CPU, runs a little warmer now, so I am considering de-lidding it. (Previous BIOS was rock solid on voltage with low LLC, now it needs a lot more) And rebuilding my 4770k system and trying my hand at hard tubing, if it turns out well I might redo the new rig.

Will a Core i7 7700K bottleneck two GTX 1080's in SLI?

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