Plotting speed not scaling with number of cores

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Issue Report

I have two PCs:
PC1: AMD Threadripper 3970X 32-core, quad-channel DDR4
PC2: AMD Ryzen 3950X 16-core, dual-channel DDR4.
The 3970X is basically two times the 3950X regarding all specs. It performs pretty much two times as good as the 3950X is all multi-core benchmarls and workloads I have ever done.

Both PC2 have two similar brandnew SSDs.

Environment

  • Ubuntu 22.04
  • Advanced CLI
  • PC1:
    • CPU: AMD 3970X
    • RAM: 128GB DDR4 quad-channel
      PC2:
    • CPU: AMD 3950X
    • RAM: 96GB DDR4 dual-channel
      Farmers are started with:
./farmer farm \
--farm-during-initial-plotting \
--reward-address xyz \
path=/media/user/SSD,size=7810000000K

CPU load on 3950X is around 50% (htop average).
CPU load on 3970X is around 35% (htop average).

Problem

According to the logs the plotting speeds (1h average) are:

  • 3950X: 4.03 MiB/s
  • 3970X: 3.19 MiB/s

How can 16 cores perform better than 32 cores?

I tried to start the farmer on the 32-core system like this:

./farmer farm \
--farm-during-initial-plotting \
--reward-address xyz \
--replotting-thread-pool-size 64 \
--plotting-thread-pool-size 64 \
--farming-thread-pool-size 32 \
path=/media/user/SSD,size=7810000000K

But this did not change anything at all.

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