An interrupt arrives
The Entry Path told the syscall half of the entry
The IRQ subsystem
How an Interrupt Reaches the Kernel ended at
Hard IRQ context
What a handler may not do, why each rule follows from the context, and the pressure that creates the rest of the folder.
Softirqs
The fixed set, why it is fixed, the budget that stops it starving everything else, and the si column in top.
Tasklets
The model, its serialisation guarantee, the problems that deprecated it, and what to use instead.
Workqueues
Deferred work in process context, so it may sleep — plus the cancel-versus-free lifetime bug everyone writes once.
Threaded IRQs
A quick primary handler plus a schedulable thread, and why PREEMPT_RT makes nearly every handler threaded.
Affinity
/proc/interrupts read column by column, MSI-X vectors per queue, and why pinning an interrupt near its consumer matters.
Timekeeping
How a clocksource is chosen, what each CLOCK* actually measures, and the lockless read path behind clockgettime.
The tick and NOHZ
What the periodic tick was doing, what turning it off moves elsewhere, and CPU isolation for latency-sensitive work.
Timers
The timer wheel's deliberate imprecision, hrtimers with real deadlines, and which one a driver should choose.
Delays and sleeps
Busy-wait delays, sleeping delays, and the guarantee every one of them lacks.