Does dual RTX 3090 require motherboard support to use nvlink? Can it be used directly without SLI under the ubuntu system? Need SLI under windows?

Gaming and Visualization Technologies General Topics & Other SDKs
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I have two RTX 3090 GPUs and I found that if I could connect them using NVLINK, the training time of my program would be faster. But I’m not sure if using nvlink requires the motherboard to support nvlink. I found that using nvlink on a Windows system requires the motherboard to support SLI. On a Linux system, just use nvlink to connect the two GPUs and set it up in the terminal. So does nvlink require motherboard support? Or is this related to which operating system (windows or linux)? Is it possible if I only need to use nvlink to connect two graphics cards under the Linux system?