Multithreaded compression offers only a slight performance improvement

I used an 11.5 GB file to test the compression times under both single-threaded and multithreaded. Multithreading with `ZSTD_c_nbWorkers`, while single-threaded does not. The results show that single-threaded compression took 35.924 seconds, whilst multithreading took 33.879 seconds. Strangely, the efficiency gain from multithreading is minimal, could you explain why this is the case?