Definition
Kernel-Level Thread
A kernel-level thread (KLT) is a thread managed directly by the operating system kernel. The kernel maintains context information for both the process and its individual threads.
In this model, the OS provides a thread API, and the kernel scheduler handles the assignment of individual threads to CPU cores.
Mechanism
- Management: The kernel handles thread creation, termination, and scheduling.
- Multiprocessing: Unlike User-Level Threads, the kernel can schedule multiple threads from the same process on different processors simultaneously.
- Blocking: If one thread blocks (e.g., on a system call), the kernel can schedule another thread from the same process to run.
- Overhead: Switching between threads requires a mode switch to kernel mode, making it slower than user-level switching.
Hybrid Models
Some modern systems use a hybrid approach (combined ULT/KLT), attempting to combine the efficiency of user-level switching with the parallel performance of kernel-level scheduling.