Arduino Clock Rate selection 400-500-600MHz do not change the Maixduino clock

There are three selections for the Maixduino within the Arduino IDE based on clock rate (400,500,600 MHz). I assumed this changed the Maixduino clock rate when selected. But no matter what I select the downloaded programs all run at exactly the same rate. I have tested this with the CoreMark benchmark.

Does anyone know how to make this work?
Thanks,
Bill

Same here
somebody answered there to set using
sysctl_cpu_set_freq(F_CPU);

but never tried