System call overhead
Each call to the kernel must perform a switch from user mode to supervisor mode, and then back again. This takes time, which can become a performance bottleneck if the calls are frequent. Furthermore, the overhead is very much non-predictable, which has a negative performance impact on real-time applications.
NVMStack software by-pass system and using polling mode, user space drivers to avoid system calls, it reduce system call overhead and bring high performance.