Only affects 64b-2t1c-avf-eth-l2xcbase-eth-2memif-1dcr (drv_vfio_pci performance difference is less than 5%).
Differences:
+ 2n-skx: +16.7 +-0.2
+ 2n-clx: +20.3 +-1.3
+ 3n-skx: +10.8 +-0.4

Preliminary examination found both the clang change [0] (direct per-patch, probably MRR, probably 2n-skx) and [1] which does not seem to be a performance-affecting change at a first glance (bisect on 2n-clx).

Possibly, skx and clx performance is affected differently by several changes.

[0] https://gerrit.fd.io/r/c/vpp/+/26744
[1] https://gerrit.fd.io/r/c/vpp/+/24053