On Mon, 13 Oct 2025 15:39:32 +1100
David Gibson
On Mon, Oct 13, 2025 at 09:31:41AM +0800, Yumei Huang wrote:
The values are adjusted to better match results observerd on the test hardware with 56-core Xeon Gold 6330 CPU and 126 GB RAM.
Interesting. That CPU is older than the one on my laptop (i7-12800H), which comfortably hit the old thresholds, but by less than a year (Q2 2021 versus Q1 2022). At the same time it's a much fancier model for its generation. I thought the Xeons might have been built with better memory bandwidth which probably has more effect on passt than the CPU's computational speed.
I'm not certain what machine Stefano was using to estimate the existing thresholds, but I'm guessing it was passt.top which is an AMD Ryzen 5 3600 - older than both of the above (2019).
Yep.
passt is single threaded so the Xeon's many cores wouldn't help it, but it's still surprising that it can't keep up with the other machines we've tried on.
Kernels and LSMs might make a huge difference as well. I expect a substantial system call overhead (because that's what it is here, I guess?) might come from SELinux hooks. Not that it really matters, I think, as long as numbers are reasonable (and we don't make them worse with some unsuspecting change) I don't see an actual problem with it. -- Stefano