It is the ninth part of the [linux-insides](https://www.gitbook.com/book/0xax/linux-insides/details) book and in the previous [Previous part](http://0xax.gitbooks.io/linux-insides/content/interrupts/interrupts-8.html) we saw implementation of the `init_IRQ` from that defined in the [arch/x86/kernel/irqinit.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/irqinit.c) source code file. So, we will continue to dive into the initialization stuff which is related to the external hardware interrupts in this part.
It is the nine part of the Interrupts and Interrupt Handling in the Linux kernel [chapter](http://0xax.gitbooks.io/linux-insides/content/interrupts/index.html) and in the previous [Previous part](http://0xax.gitbooks.io/linux-insides/content/interrupts/interrupts-8.html) we saw implementation of the `init_IRQ` from that defined in the [arch/x86/kernel/irqinit.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/irqinit.c) source code file. So, we will continue to dive into the initialization stuff which is related to the external hardware interrupts in this part.
After the `init_IRQ` function we can see the call of the `softirq_init` function in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c). This function defined in the [kernel/softirq.c](https://github.com/torvalds/linux/blob/master/kernel/softirq.c) source code file and as we can understand from its name, this function makes initialization of the `softirq` or in other words initialization of the `deferred interrupts`. What is it deferreed intrrupt? We already saw a little bit about it in the ninth [part](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-9.html) of the chapter that describes initialization process of the Linux kernel. There are three types of `deferred interrupts` in the Linux kernel:
Yangjing Zhang
8 years ago