v5.1.0 - lightning - low cpu usage

[glkappe]

tidb：v5.0.3 lightning: v5.1.0 single table、single lightning process data scale source file count 34w，dump files size is 3.2TB

in lightning log, 「engine close start」 During this time there are many "engine close start" and no "engine close compacted", and no "restore file start"

Please help explain this phenomenon and explain the principle

[glkappe]

@glorv

[sleepymole]

Lightning doesn't guarantee to utilize 100% of the cpu. So this issue should be an enhancement.