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After looking up several benchmark tests that measure the impact different PCI-Express setups have on graphics card performance, I was pretty surprised. It seems almost across the board, halving the lanes from 16 to 8 as well as testing between different generations has an insignificant impact. I am trying to understand why.
I understand that a large bottleneck for running computations on a GPU is copying memory to and from the GPU's VRAM. How then is it possible that doubling the number of lanes does barely a thing? My guesses are card drivers are locked to using up to 8 lanes; My assumption that copy time is significant when compared to the actual computation is incorrect; and/or there are a lot more constraints I don't know about (which is obviously true).
A quick google search will get you to several seemingly credible benchmarks.
Here are the top 2 from my search:
https://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518
http://www.gamersnexus.net/guides/2488-pci-e-3-x8-vs-x16-performance-impact-on-gpus
I've seen a lot of posts and articles clearly indicating the lack of a difference between setups, but none have explained why at an acceptable level.
Dan
Posted 2016-08-24T05:08:58.487
Reputation: 11
These benchmarks all measured gaming and rendering, not computation. With gaming, the textures and such are already on the GPU and the results aren't needed off the GPU. – David Schwartz – 2016-08-24T10:37:15.790
@David I think that answers it then. Thanks for this clarification – Dan – 2016-08-25T00:28:30.247