However, until 2.6 kernels, the kernel itself was not preemtible : as soon as one thread has entered the kernel, it could not be preempted to execute an other thread. The processor could be used to execute another thread when a syscall was terminated, or when the current thread explictly asked the scheduler to run another thread using the schedule() function. This means that an infinite loop in the kernel code blocked the entire system, but this is not really a problem : the kernel code is designed so that there are no infinite loops.

However, this absence of preemption in the kernel caused several problems with regard to latency and scalability. So, kernel preemption has been introduced in 2.6 kernels, and one can enable or disable it using the CONFIG_PREEMPT option. If CONFIG_PREEMPT is enabled, then kernel code can be preempted everywhere, except when the code has disabled local interrupts. An infinite loop in the code can no longer block the entire system. If CONFIG_PREEMPT is disabled, then the 2.4 behaviour is restored.

【 在 hgoldfish 的大作中提到: 】
: 是不是 ANDROID 的内核都会启用这个宏？
: 日常使用中，服务端和桌面使用的话，会不会有什么常用模块没有适配好？
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