广播模式

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/* * Periodic broadcast: * - invoke the broadcast handlers */static void tick_do_periodic_broadcast(void){raw_spin_lock(&tick_broadcast_lock);cpumask_and(to_cpumask(tmpmask),                           //确定受影响的CPU    cpu_online_mask, tick_get_broadcast_mask());tick_do_broadcast(to_cpumask(tmpmask));                    //raw_spin_unlock(&tick_broadcast_lock);}

tick_do_broadcast():

/* * Broadcast the event to the cpus, which are set in the mask (mangled). */static void tick_do_broadcast(struct cpumask *mask){int cpu = smp_processor_id();struct tick_device *td;/* * Check, if the current cpu is in the mask */if (cpumask_test_cpu(cpu, mask)) { //当前CPU是否处于广播的掩码中？cpumask_clear_cpu(cpu, mask); //从掩码中移除该CPUtd = &per_cpu(tick_cpu_device, cpu);td->evtdev->event_handler(td->evtdev); //对当前CPU调用event_handler}if (!cpumask_empty(mask)) {  //掩码中是否还有更多的CPU/* * It might be necessary to actually check whether the devices * have different broadcast functions. For now, just use the * one of the first device. This works as long as we have this * misfeature only on x86 (lapic) */td = &per_cpu(tick_cpu_device, cpumask_first(mask));/**对与局部APIC来说，broadcast方法指向lapic_timer_interrupt。对所有与不同时钟设备相关联的CPU，该方法负责*发送处理器中断LOCAL_TIMER_VECTOR，该中断的中断向量由内核设置为调用apic_timer_interrupt。其结果就是，时钟*事件设备无法区分IPI和真正的中断，因而其效果与设备仍然处于工作状态是相同的。*/td->evtdev->broadcast(mask);}}