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AMD 3990 CPU scaling tests: Because of the Windows group limit of 64 CPUs, just firing up a lot of C++ std::threads didn't work great:

128 t = 67 s
64 t = 63 s
32 t = 84 s
16 t = 160 s
8 t = 312 s

32 to 64 threads wasn't a big boost, and 64 to 128 was slower. However! \
Setting the group explicitly let it scale all the way up:

128 t = 38 s
64 t = 48 s
32 t = 84 s
16 t = 160 s
8 t = 312 s

Notably, because each group gets 32 hyperthreaded cores, 64 threads across 2 groups on an unloaded system is much faster because they are all alone on a core\
instead of shared two to a core. That means that if you don't want to add the windows group code, you are better off disabling hyperthreading and having 64 single thread cores in a single group.

I expected this code to be memory bound sooner, I'm impressed with the scalability!
I just ran the same code on a 96 vCPU google cloud instance, and it took 207 seconds using all 96 vCPU across two groups. I'm not going to wait around for any of the slower counts to finish. That is an $8k/month instance, and it is less than 1/5 the speed.
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