In CSIT report for 2101, comparison table [0] shows many NAT44ed test have worse performance compared to 2009 (generally around 5-10 percent). Mainly CPS tests, which exercise the slow path.

Bisection identified this [1] change as the cause.

Running per-patch job on that change shows a regression ([2], -5%) also in a new throughput test, which exercises the fast path.
As the two test types use stateful traffic generator mode, their results show greater variance. So I also run a test ([3], -9%) with stateless traffic (in2out direction only, fast path contrary to what the comment claims).

The change [1] claims to be an improvement, with the goal of simplifying the NAT processing logic, so maybe some regression could be expected. But commit message mentions a speed up, although I am not sure which tests would show such a speed up.
Overall, I deem it likely the change has introduced a processing inefficiency somewhere, and it could get fixed. If the regression is expected for legitimate reasons, they should be documented somewhere.

[0] https://docs.fd.io/csit/rls2101/report/_static/vpp/performance-changes-2n-clx-xxv710-2t1c-pdr.txt
[1] https://gerrit.fd.io/r/c/vpp/+/29983
[2] https://gerrit.fd.io/r/c/vpp/+/29983/29#message-27c964d4fbd1baa6645e80212c659997b1dea838
[3] https://gerrit.fd.io/r/c/vpp/+/29983/29#message-85334390efa669a5d21e05d6accc9f1b70d43fac