Thunderbolt provides a tunneling mechanism for PCIe, DisplayPort, USB etc. It's also a mesh network where packets are source-static routed from node to node in the network - so the source sets up the route-to-the-destination and the data packet is transmitted from controller-node to controller-node until it gets to the destination, then it's unpacked and presented as data to the system.
You could see some of this on the venerable "trashcan" Mac Pro, where one of the TB controllers wasn't directly connected to the port, but came through another TB node. The latencies on the ports connected to this TB controller were slightly higher due to the extra transit-time.
Latencies over PCIe are measured in tens of nanoseconds (say 70-100) depending on chipset and how much you pay. Latencies over TB can be several hundreds of nanoseconds. TB presents as a PCI interface, but that's an adaptor-type design pattern, it's not fundamentally PCIe underneath.
Thunderbolt provides a tunneling mechanism for PCIe, DisplayPort, USB etc. It's also a mesh network where packets are source-static routed from node to node in the network - so the source sets up the route-to-the-destination and the data packet is transmitted from controller-node to controller-node until it gets to the destination, then it's unpacked and presented as data to the system.
You could see some of this on the venerable "trashcan" Mac Pro, where one of the TB controllers wasn't directly connected to the port, but came through another TB node. The latencies on the ports connected to this TB controller were slightly higher due to the extra transit-time.
Latencies over PCIe are measured in tens of nanoseconds (say 70-100) depending on chipset and how much you pay. Latencies over TB can be several hundreds of nanoseconds. TB presents as a PCI interface, but that's an adaptor-type design pattern, it's not fundamentally PCIe underneath.