2023 Mac Pro M2 Ultra: Dropping CPU Performance at 3 or more CPU Cores

The M2 Ultra chip has 16 performance cores and 8 efficiency cores.

Once 17 or more CPU cores are used, a drop in per CPU performance can be expected, since the efficiency cores are slower than the performance cores.

2023 Mac Pro M2 Ultra: Per CPU Performance Variation

BSHA512 hashing speed with 1 or 2 CPU cores is notably faster than 3..16 CPU cores.

The per-CPU slowdown with 3+ cores is presumably not related to memory bandwidth, because from 3...16 CPU cores the speed is invariant.

Could there be a favored/faster die in the bifurcated M2 Ultra chipset?

The M1 Max CPU shows the same behavioral pattern (8 performance cores, 2 efficiency cores), so it looks like a “family” trait.

macOS Ventura: wildly differing CPU performance, degraded vs rebooted