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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.
What is Ksoftirqd?
A ksoftirqd is a per-CPU kernel thread raised to handle unserved software interrupts: In the preceding top sample from my personal computer, you can see ksoftirqd/n entries, where n is the CPU number that the ksoftirqds runs on.
What is Khungtaskd?
“Khungtaskd” is special kernel thread which gets scheduled every 120 seconds and check status of all process. For all processes with TASK_UNINTERRUPTIBLE state.
Is an interrupt an exception?
Interrupt is one of the classes of Exception. Events like this are called interrupts. Interrupts can be caused by either software or hardware faults. Hardware interrupts are called Interrupts, while software interrupts are called Exceptions.
When is the interrupt handler added to the kernel?
When the interrupt is signaled while the CPU is executing a kernel thread (and kernel codepath has not temporarily disabled interrupts for some critical section), the interrupt handling CPU will be added to the kernel thread in %sys mode.
Are there any interrupt priorities in the Linux kernel?
It is also difficult to support defining a generic scheme for interrupt priorities for general use OSes and some kernels (Linux included) do not use interrupt priorities. On the other hand most RTOS use interrupt priorities since they are typically used in more constraint use-cases where it is easier to define interrupt priorities.
When do interrupts happen in a Linux system?
Interrupts can happen “randomly” at any time, depending on when hardware devices raise them for the CPU. When an interrupt is signaled when the CPU happens to be running some application thread running in user-mode, the interrupt handling CPU cycles will be accounted to the application process (as you’d see in top) and as %usr type usage.
Can a Linux distro report zero interrupt time?
TL;DR: Some Linux distros and even different kernel versions within a distro have disabled IRQ time accounting. In such case, your monitoring tools will report zero time spent in hardware interrupt handlers (shown as %hi, %irq, hiq, etc).