为什么禁用中断会禁用内核抢占以及自旋锁如何禁用抢占 [英] Why disabling interrupts disables kernel preemption and how spin lock disables preemption

问题描述

我最近正在阅读 Linux内核开发，并且我有一些有关禁用抢占的问题.

I am reading Linux Kernel Development recently, and I have a few questions related to disabling preemption.

1. 在第7章的中断控制"部分中，内容为:

1. In the "Interrupt Control" section of chapter 7, it says:

此外，禁用中断也会禁用内核抢占.

Moreover, disabling interrupts also disables kernel preemption.

我还从书中读到，在以下情况下可能会发生内核抢占:

I also read from the book that kernel preemption can occur in the follow cases:

当中断处理程序退出时，返回到内核空间之前.
当内核代码再次被抢占时.
如果内核中的任务显式调用schedule()
如果其他内核中的任务阻塞(导致调用schedule())

When an interrupt handler exits, before returning to kernel-space.
When kernel code becomes preemptible again.
If a task in the kernel explicitly calls schedule()
If a task in ther kernel blocks (which results in a call to schedule())

但是我不能将禁用中断与这些情况联系起来.

But I can't relate disabling interrupts with these cases.

据我所知，自旋锁将使用 preempt_disable()函数禁用抢占.

As far as I know, a spinlock would disable preemption with the preempt_disable() function.

帖子"spin-locks"到底是什么? 说:

在单核计算机上，自旋锁只是一个禁用中断"或提高IRQL"，可完全阻止线程调度.

On a single core machine a spinlock is simply a "disable interrupts" or "raise IRQL" which prevents thread scheduling completely.

preempt_disable()是否通过禁用中断来禁止抢占?

Does preempt_disable() disable preemption by disabling interrupts?

推荐答案

我不是调度专家，但是我想解释一下我的看法. 这是几件事.

I am not a scheduler guru, but I would like to explain how I see it. Here are several things.

1. preempt_disable()不禁用IRQ .它只是增加了thread_info->preempt_count变量.
2. 禁用中断也将禁用抢占，因为调度程序在此之后不起作用-仅在单CPU计算机上起作用.在SMP上这还不够，因为当您关闭一个CPU上的中断时，另一个/其他CPU仍会/异步地执行某些操作.
3. 大锁"(意味着-关闭所有CPU上的所有中断)正在极大地降低系统速度-这就是为什么不再使用它的原因.这也是preempt_disable()无法关闭IRQ的原因.

1. preempt_disable() doesn't disable IRQ. It just increases a thread_info->preempt_count variable.
2. Disabling interrupts also disables preemption because scheduler isn't working after that - but only on a single-CPU machine. On the SMP it isn't enough because when you close the interrupts on one CPU the other / others still does / do something asynchronously.
3. The Big Lock (means - closing all interrupts on all CPUs) is slowing the system down dramatically - so it is why it not anymore in use. This is also the reason why preempt_disable() doesn't close the IRQ.

您可以看到什么是preempt_disable().试试这个: 1.获得一个自旋锁. 2.致电schedule()

You can see what is preempt_disable(). Try this: 1. Get a spinlock. 2. Call schedule()

在dmesg中，您将看到类似"BUG:原子调度"的内容.当调度程序在原子(非抢先)上下文中检测到您的进程但自行调度时，就会发生这种情况.

In the dmesg you will see something like "BUG: scheduling while atomic". This happens when scheduler detects that your process in atomic (not preemptive) context but it schedules itself.

祝你好运.

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