I have a program that is embarrassing parallel.
On my older computer which has an epyc 7302 (16 cores,  32 threads) it 
scales very well using cygwin, and fully utilized all threads.
On my new computer which has an epyc 7B13 (64 cores, 128 threads) it 
does not scale very well.

According to the windows task manager, it only uses 74% of the cpu 
resources.
The time it takes the program to run on windows is 166 seconds.
Using the same hardware on a recent version of linux, I can get 100% cpu 
utilization and the program takes 100 seconds to run.

I suspect there may be something in cygwin that doesn't scale well with 
lots of posix threads.
I know this is a bit of an unusual situation, but you can buy a 128 core 
/ 256 thread system now.

Enclosed is the output of cygcheck.
I updated my version of cygwin to be current as of today, Sep 2 2023.

thanks,
jeff