What are kernel interrupts?
An interrupt is an event that alters the normal execution flow of a program and can be generated by hardware devices or even by the CPU itself. When in interrupt occurs the current flow of execution is suspended and interrupt handler runs. After the interrupt handler runs the previous execution flow is resumed.
Can interrupts occur in kernel mode?
The interrupt handling code (part of OS) is executed in kernel mode. The interrupt vector can be modified only in kernel mode.
What type of multitasking does Linux use?
preemptive multitasking
From the process management point of view, the Linux kernel is a preemptive multitasking operating system. As a multitasking OS, it allows multiple processes to share processors (CPUs) and other system resources. Each CPU executes a single task at a time.
What is Loc interrupt?
The local timer interrupt is a timer implemented on the APIC that interrupts only a particular CPU instead of raising an interrupt that can be handled by any CPU. It’s discussed in Bovet & Cesati’s “Understanding the Linux Kernel”.
What is IRQ in computer?
(Interrupt ReQuest) A hardware interrupt on a PC. There are 16 IRQ lines used to signal the CPU that a peripheral event has started or terminated. Except for PCI devices, two devices cannot use the same line. If a new expansion card is preset to the IRQ used by an existing board, one of them must be changed.
What are Linux interrupts?
An interrupt is simply a signal that the hardware can send when it wants the processor’s attention. Linux handles interrupts in much the same way that it handles signals in user space. For the most part, a driver need only register a handler for its device’s interrupts, and handle them properly when they arrive.
How does an ISR work?
An interrupt service routine (ISR) is a software routine that hardware invokes in response to an interrupt. ISR examines an interrupt and determines how to handle it executes the handling, and then returns a logical interrupt value. If no further handling is required the ISR notifies the kernel with a return value.
Which instruction is used to load interrupts?
Read Interrupt Mask (RIM) – This instruction is used to read the status of the hardware interrupts (RST 7.5, RST 6.5, RST 5.5) by loading into the A register a byte which defines the condition of the mask bits for the interrupts. It also reads the condition of SID (Serial Input Data) bit on the microprocessor.
Is Linux multi processor?
The most significant change in 2.6 Linux Kernel which improved scalability in multi processor system was in the kernel process scheduler. The design of Linux 2.6 scheduler is based on per cpu runqueues and priority arrays, which allow the scheduler perform its tasks in O(1) time.
What are Linux multitasking?
GNU/Linux is a multi-tasking OS; a part of the kernel called the scheduler keeps track of all the programs running and allots processor time accordingly, effectively running several programs simultaneously.
What is the purpose of rescheduling interrupts in Linux?
Rescheduling interrupts are the Linux kernel’s way to notify another CPU-core to schedule a thread. On SMP systems, this is done by the scheduler to spread the load across multiple CPU-cores. The scheduler tries to spread processor activity across as many cores as possible.
When is an interrupt unexpected in the Linux kernel?
An interrupt is unexpected if it is not handled by the kernel, that is, either if there is no ISR associated with the IRQ line, or if no ISR associated with the line recognizes the interrupt as raised by its own hardware device.
How does the interrupt handler work in Linux?
The interrupt handler executes several interrupt service routines (ISRs). Each ISR is a function related to a single device sharing the IRQ line.
How is an exception handled in the Linux kernel?
4.6. Interrupt Handling – Understanding the Linux Kernel, 3rd Edition [Book] As we explained earlier, most exceptions are handled simply by sending a Unix signal to the process that caused the exception.