Hey everyone! I'm really curious about whether an unused PCIe switch adds latency to the system. Most motherboards (except for AsRock) seem to use these switches to manage PCIe 5.0 lanes from the x16 slot, especially when it comes to sharing lanes with additional components like a second M.2 SSD. If I'm not using that second SSD and all 16 lanes are directed to my graphics card, does routing them through the switch instead of a direct connection to the CPU introduce any extra latency? Since we optimize for minimal latency and maximum performance, I wonder if I'm missing something. What do you all think?
3 Answers
From what I understand, the switch itself doesn’t process data. It just reroutes the connections, which shouldn't really add latency. You're mostly just making sure wires are connected in the right way. So, it seems like all the lanes should still operate at full speed without any slowdown from the switch.
That's a good point, but some sources say that PLX chips, which are types of PCIe switches, can indeed add some latency—around 100ns typically. So, while it might not be significant for most tasks, if you're all about that low-latency life, it’s worth considering.
I've looked into this as well, and it seems that people suggest a PCIe switch can add somewhere between 250ns to 500ns of roundtrip latency, depending on how it's configured. Just to put that in perspective, that’s longer than the time it takes for one RAM clock cycle with DDR5 at regular speeds. Could be a dealbreaker if you’re really pushing for peak performance!
Related Questions
Lenovo Thinkpad Stuck In Update Loop Install FilterDriverU2_Reload