4.1Linux-kernel-softirq.1

here in kernel/softirq.c we know at the boot time,it registers a smp_hotplug_thread task,then whenever a cpu is online, we create one corresponding kernel thread,the thread function is run_ksoftirqd,we could know by following the routine :disable hardware irq by calling local_irq_disable,this is enforced on local cpu. this guarantees that softirq context is atomic .