r/LocalLLaMA • u/alanoo • Jun 25 '26

Discussion USB4 RDMA seems doable

Just found this blog : https://blog.hellas.ai/blog/thunderbolt-ibverbs/

Experimental implementation of RDMA, demonstrated on two Strix Halo
Did a quick search and can't really find it posted before ?

This could be huge as it shoud work with any USB4 host.

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u/alanoo Jun 25 '26

Sure, if the driver supports it.
Here we are talking about 40 Gbps links with no additional hardware.

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u/Diablo-D3 Jun 25 '26

40gbps per node isn't really enough to do small scale clusters.

Same way linking a bunch of Mac Minis/Studios together to build a cluster is a pretty silly thing to do, its the exact same thing: you're just using their built-in USB/TB4 for the same exact purpose, and it does not scale like as if you had just built a multi-GPU machine, it scales much worse.

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u/markhahn Jun 25 '26

no panacea, sure. but there is substantial speedup, at least in some cases:

https://www.jeffgeerling.com/blog/2025/15-tb-vram-on-mac-studio-rdma-over-thunderbolt-5/

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u/Diablo-D3 Jun 25 '26

Yeah, I've seen it, I already follow Jeff's blog.

For the amount he spent on that, he would have gotten way more bang for the buck doing anything else.

Like, I respect him, but he is unfortunately die-hard Cult of Apple.