investigate AMD Shani loops

[potuz]

The following is a bench on intel

[ RUN      ] shani.shani
[       OK ] shani.shani (mean 2.513ms, confidence interval +- 0.416409%)
[ RUN      ] shani.shani_one_at_time
[       OK ] shani.shani_one_at_time (mean 2.588ms, confidence interval +- 0.422037%)

And these are on AMD:

[ RUN      ] shani.shani
[       OK ] shani.shani (mean 2.271ms, confidence interval +- 0.119590%)
[ RUN      ] shani.shani_one_at_time
[       OK ] shani.shani_one_at_time (mean 3.947ms, confidence interval +- 0.063440%)

They do not happen always, but there is a big difference between the one_at_time bench and the normal run. This was only reproduced on AMD