Two Nvidia GPUs possible only in x8/x8 PCI-E 3.0 configuration with i9-9900K?

[rohitgupta1975]

I am planning to NvLink two RTX 2080 Ti cards in a Z390 motherboard with a i9-9900K CPU. Will I be limited x8/x8 PCI-E mode? Or can I also do x16/x16 or x16/x8 ?

(I have seen benchmarks showing that for "supported" games, FPS for x16/x16 > x16/x8 > x8/x8 )

 

[Lutfij]

Mind sharing the links to your benchmarks? You're asking for info on tech that hasn't even ended up in reviewers hands.

 

[rohitgupta1975]

Mind sharing the links to your benchmarks? You're asking for info on tech that hasn't even ended up in reviewers hands.

The benchmarks I am referring to use older GPUs. But that should apply to any GPU(s), not specifically the RTX series. x8/x8 mode will limit the bandwidth between the CPU and GPUs compared to x16/x8 or x16/x16 modes.

Let me re-phrase then: Will I be limited to x8/x8 mode if I SLI/NvLink two Nvidia GPUs (e.g. 1080 Ti) on a Z390 mobo with an i9-9900K ?

 

[SkyNetRising]

Z390 is not out either.
From leaked specs possible PCIE configs are - x16, x8/x8, x8/x4/x4
https://www.anandtech.com/show/13135/more-details-on-intels-z390-chipset-exposed

 

[rohitgupta1975]

Z390 is not out either.
From leaked specs possible PCIE configs are - x16, x8/x8, x8/x4/x4
https://www.anandtech.com/show/13135/more-details-on-intels-z390-chipset-exposed

@skynetrising As per the link you sent, processor PCIe configurations supported are as you wrote. So these configurations are limited by the i9-9900K ? (which I suppose supports max of 16 PCIe lanes)

In that case, two SLI-ed GPUs will be bottle-necked by x8/x8 mode. Ideally, for the best performance, I would have liked x16/x16 for the demanding games that are coming out.

 

[SkyNetRising]

PCIE 3.0 x8 doesn't bottleneck anything on currently available hardware.
Not sure, how this is going to be on RTX 2080 Ti though. Probably also not a problem.

 

[rohitgupta1975]

PCIE 3.0 x8 doesn't bottleneck anything on currently available hardware.
Not sure, how this is going to be on RTX 2080 Ti though. Probably also not a problem.

As per this 2-year old benchmark for Titans X (Pascal), x8/x8 was almost always slower than x16/x16 .

Link: https://www.pugetsystems.com/labs/articles/Titan-X-Performance-PCI-E-3-0-x8-vs-x16-851/

So this is why I started this thread and this is why I am unsure if I should go for an X299 chipset with an X-series CPU (that has support for 24 processor PCIe lanes, allowing x8/x16 mode) or should I bring the upcoming Intel chipset and CPU (Z390/i9-9900K) home (when available). In the end, I want to SLI and want the best performance out of the cards. Not sure which chipset/CPU will give me that.

 

[bmockeg]

I wouldn't try to sli in 2018 in the first place. Waste of money.

 

[6d-ai]

Another variable is that RTX uses NVLink, not the traditional SLI bridge. That is supposed to help scaling and possibly help offload PCIE bandwidth. The bridge alone costs US$600. Before dropping US$3k on a graphics solution wait for benchmark data to make a decision. Too many unknowns at this point.

 

[rohitgupta1975]

Thanks 6d-ai/bmockeg/skynetrising/lutfij for the inputs.

 

[bmockeg]

If you decide to sli, the performance drop is usually only 1-2% with a 2nd card in 8x. However, DirectX 12 doesnt support SLI and many DirectX 11 games have stopped as well. IMO, your best bet is to get a single 2080ti if,the benchmarks are solid.

 

[kerberos_20]

with direct x12 apps can use as many gpus u have no matter brands (explicit multi-gpu)
but u know how lazy developers are

 

[adirtypir8]

Another variable is that RTX uses NVLink, not the traditional SLI bridge. That is supposed to help scaling and possibly help offload PCIE bandwidth. The bridge alone costs US$600. Before dropping US$3k on a graphics solution wait for benchmark data to make a decision. Too many unknowns at this point.

lol $600