←back to thread

io_uring is faster than mmap

(www.bitflux.ai)
283 points ghuntley | 1 comments | 04 Sep 25 22:01 UTC | HN request time: 0.001s | source
Show context
modeless ◴[05 Sep 25 03:25 UTC] No.45134728[source]▶
Wait, PCIe bandwidth is higher than memory bandwidth now? That's bonkers, when did that happen? I haven't been keeping up.

Just looked at the i9-14900k and I guess it's true, but only if you add all the PCIe lanes together. I'm sure there are other chips where it's even more true. Crazy!

replies(4): >>45134749 #>>45134790 #>>45135433 #>>45136511 #
adgjlsfhk1 ◴[05 Sep 25 03:30 UTC] No.45134749[source]▶
on server chips it's kind of ridiculous. 5th gen Epyc has 128 lanes of PCIEx5 for over 1TB/s of pcie bandwith (compared to 600GB/s RAM bandwidth from 12 channel ddr5 at 6400)
replies(1): >>45134783 #
andersa ◴[05 Sep 25 03:40 UTC] No.45134783[source]▶
Your math is a bit off. 128 lanes gen5 is 8 times x16, which has a combined theoretical bandwidth of 512GB/s, and more like 440GB/s in practice after protocol overhead.

Unless we are considering both read and write bandwidth, but that seems strange to compare to memory read bandwidth.

replies(2): >>45134856 #>>45135199 #
wmf ◴[05 Sep 25 05:18 UTC] No.45135199[source]▶
PCIe is full duplex while DDR5 is half duplex so in theory PCIe is higher. It's rare to max out PCIe in both directions though.
replies(1): >>45135223 #
1. mrcode007 ◴[05 Sep 25 05:24 UTC] No.45135223{3}[source]▶
happens frequently in fact when training neural nets on modern hw