Ploting on Ryzen 3100, 16GB ram, 1GB NVME, B450 MB, Ubuntu 20.10.....slow parallel plots

Hi there,
My plan was , as I have 1GB nvme (Gigabyte m.2) to plot 3 plots in parallel wth 2 threads, 4,5GB ram each. This is going vey slow…the main issue is that I could not employ CPU 100%. The 3 paralel plots needs 24 hours to finish.
Even with “all IN” …single plot with 8 threads, 12GB RAM, the CPU is less than 50% utilized, and the ploting time is more than 11 hours…
I made several experiments with different settings, suposing that CPU is a bottleneck, so 2 parallel plots with 4 threds each and 6GB RAM per plot should at least emply CPU…not happening. I could not find the problem.
Any ideas?

Very slow…means 1 single plot with all threads and RAM going for 11 hours. Any parallel going for 24 hours.

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