All using NetBSD 9.99.51 (XEN3_DOMU) #0: Sun Mar 22 17:35:29 UTC 2020
Note that increasing the vCPUs from 1 to 4 (2 gives same result as 4)
drops the throughput to about 10%. No offloads configured in domU:
I found out the problem appeared between 2020-01-08 00:00 (that was still good) and 2020-01-14 00:00 (that is already bad).
There were some CPU scheduling changes by Andrew Doran around that time, so it's likely the culprit.
I'm working on bisecting this further. It's complicated, between 01-08 and 01-14 there were some bugs which prevent the Xen DomU MP kernel from booting.
Jaromir