How many PCIe Extensions is TOO MANY??

I love a good “PCI Challenge”, where someone tries to see how much functionality they can wring out of PCI devices in a weird situation. Linus Tech Tips has a bunch of good ones: - How crazy of a device can you use with a server motherboard’s PCI hot-swap BIOS feature: [LINK] - How many PCI extenders can you use with a high end graphics card: [VIDEO]

It's a shame you can't get a cable to link computers via PCIe (supports cables over 3m[0]). Multiple x16 connections that would lead to some decent bandwidth while being low-latency, without the network overhead or shelling out for high-end switches. You can skip halfway. [0] [VIDEO]

Here is an LTT video about how many PCI-E extensions one can daisychain without problems. The limit is around 3 meters. [VIDEO]

LTT has a video where they tried to see how many PCIe riser cables they could string together before it stopped working.[1] They got to several meters. Maybe you could argue that it's worse inside a PC case since there's more EMI, but it seems like your PCIe riser cable would have to be very out of spec before you'd notice anything. [1] [VIDEO]

Someone needs to get this man a speed square, also a longer riser cable [1]. [1]I don't care much for Linus Tech, but [VIDEO]

PCIe is more like a packet-switched network than a bus, which is incidentally why things like Thunderbolt (effectively external PCIe) and sillier demonstrations like [VIDEO] work. ...and with things like [LINK] , you can get even higher latencies.

I wonder if that benchmark actually loaded the PCIe bus to any significant degree after the initial benchmark startup, or just updated a couple small parameters on a single scene and thus mainly just tested the local computation on the GPU? You'd want to somehow monitor the PCIe bus error rate - with a marginal signal and lots of errors -> retries, something that loads the bus harder (loading new textures etc) could suffer way more. They do briefly show a different PCIe riser made out of generic ribbon cable [1, 3:27], and say that one failed after chaining only two ~200mm lengths. The quality of the riser cable certainly matters. [1] [VIDEO]