Is the 20% perf hit of TSO mode that you cite an ARM vs. ARM comparison? If so, that would be pretty damning.
Is there an easy way to flip the M1 into TSO mode for benchmarking? I would love to observe this 20% for myself.
I haven’t verified the exact numbers myself. And it will depend on the exact thing you’re running. It’s just on the order of low tens of percents.
TSO cannot be enabled outside of rosetta as it’s not exactly a good arm extension. Perhaps you could do some trickery but Apple likely prevents that.
However you can test it by making something where you know rosetta generates comparable arm assembly from the X86 one and just run comparison that way. Some sort of parallel lockfree algorithm would be the best candidate.