Kernel preemption
Encyclopedia
Kernel preemption is a method used mainly in monolithic
and hybrid
kernel
s where all or most device drivers are run in kernel space, whereby the scheduler
is permitted to forcibly perform a context switch
(i.e. preemptively schedule; on behalf of a runnable and higher priority process) on a driver or other part of the kernel during its execution, rather than co-operatively wait for the driver or kernel function (such as a system call
) to complete its execution and return control of the processor to the scheduler.
There are two main benefits to this method in monolithic and hybrid kernels, and answer one of the main criticisms of monolithic kernels from microkernel
advocates, which is that;
Monolithic kernel
A monolithic kernel is an operating system architecture where the entire operating system is working in the kernel space and alone as supervisor mode...
and hybrid
Hybrid kernel
A hybrid kernel is a kernel architecture based on combining aspects of microkernel and monolithic kernel architectures used in computer operating systems. The category is controversial due to the similarity to monolithic kernel; the term has been dismissed by Linus Torvalds as simple marketing...
kernel
Kernel (computing)
In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...
s where all or most device drivers are run in kernel space, whereby the scheduler
Scheduling (computing)
In computer science, a scheduling is the method by which threads, processes or data flows are given access to system resources . This is usually done to load balance a system effectively or achieve a target quality of service...
is permitted to forcibly perform a context switch
Context switch
A context switch is the computing process of storing and restoring the state of a CPU so that execution can be resumed from the same point at a later time. This enables multiple processes to share a single CPU. The context switch is an essential feature of a multitasking operating system...
(i.e. preemptively schedule; on behalf of a runnable and higher priority process) on a driver or other part of the kernel during its execution, rather than co-operatively wait for the driver or kernel function (such as a system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
) to complete its execution and return control of the processor to the scheduler.
There are two main benefits to this method in monolithic and hybrid kernels, and answer one of the main criticisms of monolithic kernels from microkernel
Microkernel
In computer science, a microkernel is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system . These mechanisms include low-level address space management, thread management, and inter-process communication...
advocates, which is that;
- A device driver can enter an infinite loop or other unrecoverable state, crashing the whole system
- Some drivers and system calls on monolithic kernels are slow to execute, and can't return control of the processor to the scheduler or other program until they complete execution.