Turn off reserved cores for single-thread tasks on Pc2/C2 workers.

[Reiers]

Hi everybody! 

Worker 0, host Filecoin-Super-Server
        CPU:  [                                                                ] 0 core(s) in use
        RAM:  [|||||                                                           ] 9% 11.34 GiB/125.7 GiB
        VMEM: [|                                                               ] 2% 11.34 GiB/381.7 GiB
        GPU: TITAN RTX, not used
Worker 1, host ultron-epyc-worker
        CPU:  [||||||||||||||||||||||||||||                                    ] 7 core(s) in use
        RAM:  [|||||||||||||||||||||||||||||||||                               ] 52% 398 GiB/755.1 GiB
        VMEM: [|||||||||||||||||||||||||||||||||||||                           ] 59% 454 GiB/757.1 GiB
Worker 2, host jokasta-intel-worker
        CPU:  [||||||||||||||||||||||||||||||||||||||||||||||||||||||||||      ] 22 core(s) in use
        RAM:  [||||||||||||||||                                                ] 26% 33.14 GiB/125.5 GiB
        VMEM: [|||||||||||||||||||||||||                                       ] 40% 153.1 GiB/381.5 GiB
        GPU: GeForce RTX 2080 Ti, used
Worker 3, host jarvis-amd-worker
        CPU:  [                                                                ] 0 core(s) in use
        RAM:  [||                                                              ] 3% 4.866 GiB/125.8 GiB
        VMEM: [                                                                ] 1% 4.866 GiB/381.8 GiB
        GPU: GeForce GTX 1080 Ti, not used
Worker 4, host friday-amd-worker
        CPU:  [||||||||||||||||||||||||||||||||||||||||||||||||||||||||||      ] 58 core(s) in use
        RAM:  [||||||||                                                        ] 14% 18.59 GiB/125.7 GiB
        VMEM: [||                                                              ] 4% 18.59 GiB/381.7 GiB
        GPU: GeForce GTX 1080 Ti, used
        GPU: GeForce GTX 1080 Ti, used
Worker 5, host virgil-amd-worker
        CPU:  [                                                                ] 0 core(s) in use
        RAM:  [|                                                               ] 3% 3.903 GiB/125.7 GiB
        VMEM: [                                                                ] 1% 3.903 GiB/381.7 GiB
        GPU: GeForce RTX 2080 SUPER, not used
        GPU: GeForce RTX 2080 SUPER, not used
Worker 6, host plato-amd-worker
        CPU:  [                                                                ] 0 core(s) in use
        RAM:  [|                                                               ] 2% 2.72 GiB/125.8 GiB
        VMEM: [                                                                ] 0% 2.72 GiB/381.8 GiB
        GPU: GeForce GTX 1080 Ti, not used

lotus version 0.8.1+git.1ebad94d

This part of the update: Allow some single-thread tasks to run in parallel with PC2/C2 (#4116)
Any way to turn it off? And go back to the way it was? @magik6k
We have a dedicated PC1 Workers and we don't want to have reserved cores for single-thread tasks on our PC2/C2 Workers.

[SgtCoin]

PR merged, archiving for future reference.