4-core CPU uplinks can't run full, processes can't continue to ramp up after reaching 100% CPU usage

[lxp0826]

Hi, I am using libreSpeed, there is a performance bottleneck in upstream speed test, after the libreSpeed process CPU usage reaches 100%, the upstream speed test reaches about 850M can't continue to improve, the downstream is normal, and the CPU usage is about 14%+, please tell me how can I improve it, thank you, the CPU is J1900.