Hi xor
From the link you provided:
... All kernels were from the Ubuntu Mainline Kernel PPA and kept to their stock settings, ...
So a less misleading title would read:
"Ubuntus Linux 5.x Mainline Kernel Performance Is Sliding In The Wrong Direction"In one of the comments (you did take the time to read those, right?) someone posted benchmarks of socket throughput and latency
of Ubuntu kernels versus those he configured himself (scroll down to see the results):
https://openbenchmarking.org/result/1902248-KH-TEST1982530These results suggest it is an Ubuntu issue and that "Linux 5.x Kernel Performance Is Sliding In The Right Direction"