It's interesting, that cn/2 alias Monero v8 has different impact on different CPUs. With Zen it's relatively moderate, AMD Ryzen 7 2700 dropped from 620 H/s to 595 H/s (-4%).
On Bulldozer-based CPUs instead, it's devastating! A8-5600K "Piledriver" dropped from 155 H/s to 119 H/s (-24%), Opteron 4284 "Zambezi" from 280 H/s to 180 H/s (-35%) and A8-7600 "Kaveri" clashed from 177 H/s to 94 H/s
(-47%).
Apparently this are the archs, which were not cache limited, but are limited in execution units, pipelines and/or instructions on the fly, whereas a CPU like Ryzen is wide enough to do the extra instructions on the side.
On Bulldozer-based CPUs instead, it's devastating! A8-5600K "Piledriver" dropped from 155 H/s to 119 H/s (-24%), Opteron 4284 "Zambezi" from 280 H/s to 180 H/s (-35%) and A8-7600 "Kaveri" clashed from 177 H/s to 94 H/s
(-47%). Apparently this are the archs, which were not cache limited, but are limited in execution units, pipelines and/or instructions on the fly, whereas a CPU like Ryzen is wide enough to do the extra instructions on the side.