本文探讨了操作系统中中断处理的基本原则及其对系统性能的影响。介绍了中断处理程序仅做最少的工作并快速返回，将非关键任务推迟到稍后通过软中断或工作队列处理。讨论了软中断的静态分配及限制，并提出使用任务项来动态创建和销毁处理程序的方法。
System calls
Review:
Interrupt 只能嵌套两次
Bottomhalf (in linux)
Interrupt handling Philosophy
- Do as little as possible
- Defer non-critical actions till later
Interrupt handlers have no process context - cannot sleep
Top and bottom halves
Top-half: do minimum work and return (ISR)
Do it now!
Bottom-half: deferred processing
Do it later!
Softirqs
Statically allocated
Limited number
Can be executed simultaneously on multiple CPUs
Re-entrant
Do its own locking
Rescheduling
Softirq 的 handler 可能自己去设一个 softirq
Solution: quota + ksoftirqd
Tasklets
Softirq is static: cannot add a new type of softirq
Can be created and destroyed dynamically
Trouble: hard to get right; careful about sleeping
Work queues
Have a process context
Always run by kernel threads
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