In this technique, the kernel knows about and handles the threads. No runtime system is required in this case. In place of thread table in each process, the kernel has a thread table that keeps track of all threads in the system. As well, the kernel also maintains the traditional process table to keep track of processes. Operating Systems kernel gives system call to create and manage threads.
The implementation of common structure of kernel-level thread is
Advantages:
Since kernel has full knowledge of all threads, Scheduler may make a decision to give more time to a process having large amount of threads than process having small number of threads.
Kernel-level threads are mainly good for applications that frequently block.
Disadvantages:
The kernel-level threads are slow and inefficient. Illustration sis, threads operations are hundreds of times slower than that of user-level threads.
Kernel must handle and schedule threads as well as processes. It involves a full thread control block (TCB) for each thread to keep information about threads. As a result significant overhead and increased in kernel complexity.