Okay, now if I start to inspect the issue and try to find kernel level differences between Linux and FreeBSD, may you have ideas, which parts of these kernels would be the most promising to find some interesting differences? (differences that are clear and meaningful and so on) Where to start looking for?
Different parts of kernel are for example process management, process scheduling, system calls, data structures (lists, queues, maps, binary trees...) , interrupts - their handlers and bottom halves, synchronization (of shared resource access), timers and time management, memory management, virtual filesystem, file system representation, the block I/O layer, page cache, modules, kernel objects