User Mode and Kernel Mode
See also: Kernel preemptionIn any given system design, some operations performed by the system may not be preemptible. This usually applies to kernel functions and service interrupts which, if not permitted to run to completion, would tend to produce race conditions resulting in deadlock. Barring the scheduler from preempting tasks while they are processing kernel functions simplifies the kernel design at the expense of system responsiveness. The distinction between user mode and kernel mode, which determines privilege level within the system, may also be used to distinguish whether a task is currently preemptible.
Most modern systems have preemptive kernels, designed to permit tasks to be preempted even when in kernel mode. Examples of such systems are Solaris 2.0/SunOS 5.0, Windows NT, the Linux kernel 2.6 and 3.x, AIX and some BSD systems (NetBSD, since version 5).
Read more about this topic: Preemption (computing)
Famous quotes containing the words user, mode and/or kernel:
“A worker may be the hammer’s master, but the hammer still prevails. A tool knows exactly how it is meant to be handled, while the user of the tool can only have an approximate idea.”
—Milan Kundera (b. 1929)
“The character of the logger’s admiration is betrayed by his very mode of expressing it.... He admires the log, the carcass or corpse, more than the tree.... What right have you to celebrate the virtues of the man you murdered?”
—Henry David Thoreau (1817–1862)
“All true histories contain instruction; though, in some, the treasure may be hard to find, and when found, so trivial in quantity that the dry, shrivelled kernel scarcely compensates for the trouble of cracking the nut.”
—Anne Brontë (1820–1849)