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As a compromise, the Linux kernel uses the interrupt-driven mode by default and only switches to polling mode when the flow of incoming packets exceeds a certain threshold, known as the "weight" of the network interface.
For example, hardware interrupt threads have the highest priority, followed by software interrupts, kernel-only threads, then finally user threads. A user thread either runs at user-kernel priority (when it is actually running in the kernel, e.g. running a syscall on behalf of userland), or a user thread runs at user priority.
The interrupt priority level (IPL) is a part of the current system interrupt state, which indicates the interrupt requests that will currently be accepted. The IPL may be indicated in hardware by the registers in a programmable interrupt controller , or in software by a bitmask or integer value and source code of threads.
In systems that support privileged mode, only privileged applications (usually the OS kernel) may modify the Interrupt flag. In an x86 system this only applies to protected mode code (Real mode code may always modify the Interrupt flag). CLI and STI are privileged instructions, which cause a general protection fault if an unprivileged ...
The role of KMS (Kernel mode-setting), Linux example Wayland compositors require KMS (and also OpenGL ES and EGL ) evdev was the Linux kernel module that receives data from various Input devices such as Keyboard, Mouse, Touch-Pad, etc. Nowadays, this is the libinput module (for X and Wayland).
Some operating systems are single address space operating systems—they have a single address space for all user-mode code. (The kernel-mode code may be in the same address space, or it may be in a second address space). Other operating systems have a per-process address space, with a separate address space for each user-mode process.
Kernel page-table isolation (KPTI or PTI, [1] previously called KAISER) [2] [3] is a Linux kernel feature that mitigates the Meltdown security vulnerability (affecting mainly Intel's x86 CPUs) [4] and improves kernel hardening against attempts to bypass kernel address space layout randomization (KASLR).
Ideally, only highly trusted kernel code is allowed to execute in the unrestricted mode; everything else (including non-supervisory portions of the operating system) runs in a restricted mode and must use a system call (via interrupt) to request the kernel perform on its behalf any operation that could damage or compromise the system, making it ...