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

Aug 29, 2018
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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 )
 
Aug 29, 2018
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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 ?
 
Aug 29, 2018
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@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.
 
Aug 29, 2018
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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.



 
Sep 3, 2018
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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.
 
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.
 
Oct 2, 2018
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lol $600
 

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