Page "Thread (computing)" Paragraph 32

M: N maps some N number of application threads onto some M number of kernel entities, or " virtual processors.

" This is a compromise between kernel-level (" 1: 1 ") and user-level (" N: 1 ") threading.

In general, " M: N " threading systems are more complex to implement than either kernel or user threads, because changes to both kernel and user-space code are required.

In the M: N implementation, the threading library is responsible for scheduling user threads on the available schedulable entities ; this makes context switching of threads very fast, as it avoids system calls.

However, this increases complexity and the likelihood of priority inversion, as well as suboptimal scheduling without extensive ( and expensive ) coordination between the userland scheduler and the kernel scheduler.