static int __cpuinit blk_cpu_notify(struct notifier_block *self,
				    unsigned long action, void *hcpu)
{
	/*
	 * If a CPU goes away, splice its entries to the current CPU
	 * and trigger a run of the softirq
	 */
	if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
		int cpu = (unsigned long) hcpu;

		local_irq_disable();
		list_splice_init(&per_cpu(blk_cpu_done, cpu),
				 &__get_cpu_var(blk_cpu_done));
		raise_softirq_irqoff(BLOCK_SOFTIRQ);
		local_irq_enable();
	}

	return NOTIFY_OK;
}

void __blk_complete_request(struct request *req)
{
	int ccpu, cpu, group_cpu = NR_CPUS;
	struct request_queue *q = req->q;
	unsigned long flags;

	BUG_ON(!q->softirq_done_fn);

	local_irq_save(flags);
	cpu = smp_processor_id();

	/*
	 * Select completion CPU
	 */
	if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1) {
		ccpu = req->cpu;
		if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) {
			ccpu = blk_cpu_to_group(ccpu);
			group_cpu = blk_cpu_to_group(cpu);
		}
	} else
		ccpu = cpu;

	if (ccpu == cpu || ccpu == group_cpu) {
		struct list_head *list;
do_local:
		list = &__get_cpu_var(blk_cpu_done);
		list_add_tail(&req->csd.list, list);

		/*
		 * if the list only contains our just added request,
		 * signal a raise of the softirq. If there are already
		 * entries there, someone already raised the irq but it
		 * hasn't run yet.
		 */
		if (list->next == &req->csd.list)
			raise_softirq_irqoff(BLOCK_SOFTIRQ);
	} else if (raise_blk_irq(ccpu, req))
		goto do_local;

	local_irq_restore(flags);
}

void __blk_complete_request(struct request *req)
{
	struct request_queue *q = req->q;
	unsigned long flags;
	int ccpu, cpu, group_cpu;

	BUG_ON(!q->softirq_done_fn);
    /* 计算接收到中断的CPU */
	local_irq_save(flags);
	cpu = smp_processor_id();
	group_cpu = blk_cpu_to_group(cpu);

	/*
	 * Select completion CPU, 找到应该处理完成请求的CPU
	 */ /* QUEUE_FLAG_SAME_COMP要求提交请求的CPU来做请求完成处理 */
	if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1)
		ccpu = req->cpu;
	else
		ccpu = cpu;

	if (ccpu == cpu || ccpu == group_cpu) { /* 处理完成请求的CPU和接收请求的CPU是同一个 */
		struct list_head *list;
do_local:
		list = &__get_cpu_var(blk_cpu_done);
		list_add_tail(&req->csd.list, list); /* 将完成请求插入CPU的队列 */

		/*
		 * if the list only contains our just added request,
		 * signal a raise of the softirq. If there are already
		 * entries there, someone already raised the irq but it
		 * hasn't run yet.
		 */
		if (list->next == &req->csd.list)
			raise_softirq_irqoff(BLOCK_SOFTIRQ);
	} else if (raise_blk_irq(ccpu, req))  /* 路由中断，路由成功返回0 */
		goto do_local;

	local_irq_restore(flags);
}

int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
		unsigned long delta_ns, const enum hrtimer_mode mode,
		int wakeup)
{
	struct hrtimer_clock_base *base, *new_base;
	unsigned long flags;
	int ret, leftmost;

	base = lock_hrtimer_base(timer, &flags);

	/* Remove an active timer from the queue: */
	ret = remove_hrtimer(timer, base);

	if (mode & HRTIMER_MODE_REL) {
		tim = ktime_add_safe(tim, base->get_time());
		/*
		 * CONFIG_TIME_LOW_RES is a temporary way for architectures
		 * to signal that they simply return xtime in
		 * do_gettimeoffset(). In this case we want to round up by
		 * resolution when starting a relative timer, to avoid short
		 * timeouts. This will go away with the GTOD framework.
		 */
#ifdef CONFIG_TIME_LOW_RES
		tim = ktime_add_safe(tim, base->resolution);
#endif
	}

	hrtimer_set_expires_range_ns(timer, tim, delta_ns);

	/* Switch the timer base, if necessary: */
	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);

	timer_stats_hrtimer_set_start_info(timer);

	leftmost = enqueue_hrtimer(timer, new_base);

	/*
	 * Only allow reprogramming if the new base is on this CPU.
	 * (it might still be on another CPU if the timer was pending)
	 *
	 * XXX send_remote_softirq() ?
	 */
	if (leftmost && new_base->cpu_base == &__get_cpu_var(hrtimer_bases)
		&& hrtimer_enqueue_reprogram(timer, new_base)) {
		if (wakeup) {
			/*
			 * We need to drop cpu_base->lock to avoid a
			 * lock ordering issue vs. rq->lock.
			 */
			raw_spin_unlock(&new_base->cpu_base->lock);
			raise_softirq_irqoff(HRTIMER_SOFTIRQ);
			local_irq_restore(flags);
			return ret;
		} else {
			__raise_softirq_irqoff(HRTIMER_SOFTIRQ);
		}
	}

	unlock_hrtimer_base(timer, &flags);

	return ret;
}

//.........这里部分代码省略.........
		 * calculate the expiry time for the next timer wheel
		 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
		 * that there is no timer pending or at least extremely
		 * far into the future (12 days for HZ=1000). In this
		 * case we set the expiry to the end of time.
		 */
		if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
			/*
			 * Calculate the time delta for the next timer event.
			 * If the time delta exceeds the maximum time delta
			 * permitted by the current clocksource then adjust
			 * the time delta accordingly to ensure the
			 * clocksource does not wrap.
			 */
			time_delta = min_t(u64, time_delta,
					   tick_period.tv64 * delta_jiffies);
			expires = ktime_add_ns(last_update, time_delta);
		} else {
			expires.tv64 = KTIME_MAX;
		}

		/*
		 * If this cpu is the one which updates jiffies, then
		 * give up the assignment and let it be taken by the
		 * cpu which runs the tick timer next, which might be
		 * this cpu as well. If we don't drop this here the
		 * jiffies might be stale and do_timer() never
		 * invoked.
		 */
		if (cpu == tick_do_timer_cpu)
			tick_do_timer_cpu = TICK_DO_TIMER_NONE;

		if (delta_jiffies > 1)
			cpumask_set_cpu(cpu, nohz_cpu_mask);

		/* Skip reprogram of event if its not changed */
		if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
			goto out;

		/*
		 * nohz_stop_sched_tick can be called several times before
		 * the nohz_restart_sched_tick is called. This happens when
		 * interrupts arrive which do not cause a reschedule. In the
		 * first call we save the current tick time, so we can restart
		 * the scheduler tick in nohz_restart_sched_tick.
		 */
		if (!ts->tick_stopped) {
			if (select_nohz_load_balancer(1)) {
				/*
				 * sched tick not stopped!
				 */
				cpumask_clear_cpu(cpu, nohz_cpu_mask);
				goto out;
			}

			ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
			ts->tick_stopped = 1;
			ts->idle_jiffies = last_jiffies;
			rcu_enter_nohz();
		}

		ts->idle_sleeps++;

		/* Mark expires */
		ts->idle_expires = expires;

		/*
		 * If the expiration time == KTIME_MAX, then
		 * in this case we simply stop the tick timer.
		 */
		 if (unlikely(expires.tv64 == KTIME_MAX)) {
			if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
				hrtimer_cancel(&ts->sched_timer);
			goto out;
		}

		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
			hrtimer_start(&ts->sched_timer, expires,
				      HRTIMER_MODE_ABS_PINNED);
			/* Check, if the timer was already in the past */
			if (hrtimer_active(&ts->sched_timer))
				goto out;
		} else if (!tick_program_event(expires, 0))
				goto out;
		/*
		 * We are past the event already. So we crossed a
		 * jiffie boundary. Update jiffies and raise the
		 * softirq.
		 */
		tick_do_update_jiffies64(ktime_get());
		cpumask_clear_cpu(cpu, nohz_cpu_mask);
	}
	raise_softirq_irqoff(TIMER_SOFTIRQ);
out:
	ts->next_jiffies = next_jiffies;
	ts->last_jiffies = last_jiffies;
	ts->sleep_length = ktime_sub(dev->next_event, now);
end:
	local_irq_restore(flags);
}

//.........这里部分代码省略.........
	if (need_resched())
		return;

	if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
		static int ratelimit;

		if (ratelimit < 10) {
			printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
			       (unsigned int) local_softirq_pending());
			ratelimit++;
		}
		return;
	}

	ts->idle_calls++;
	
	do {
		seq = read_seqbegin(&xtime_lock);
		last_update = last_jiffies_update;
		last_jiffies = jiffies;
		time_delta = timekeeping_max_deferment();
	} while (read_seqretry(&xtime_lock, seq));

	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) ||
	    arch_needs_cpu(cpu)) {
		next_jiffies = last_jiffies + 1;
		delta_jiffies = 1;
	} else {
		
		next_jiffies = get_next_timer_interrupt(last_jiffies);
		delta_jiffies = next_jiffies - last_jiffies;
		if (rcu_delta_jiffies < delta_jiffies) {
			next_jiffies = last_jiffies + rcu_delta_jiffies;
			delta_jiffies = rcu_delta_jiffies;
		}
	}
	if (!ts->tick_stopped && delta_jiffies == 1)
		goto out;

	
	if ((long)delta_jiffies >= 1) {

		if (cpu == tick_do_timer_cpu) {
			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
			ts->do_timer_last = 1;
		} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
			time_delta = KTIME_MAX;
			ts->do_timer_last = 0;
		} else if (!ts->do_timer_last) {
			time_delta = KTIME_MAX;
		}

		if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
			time_delta = min_t(u64, time_delta,
					   tick_period.tv64 * delta_jiffies);
		}

		if (time_delta < KTIME_MAX)
			expires = ktime_add_ns(last_update, time_delta);
		else
			expires.tv64 = KTIME_MAX;

		
		if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
			goto out;

		if (!ts->tick_stopped) {
			select_nohz_load_balancer(1);

			ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
			ts->tick_stopped = 1;
			ts->idle_jiffies = last_jiffies;
		}

		ts->idle_sleeps++;

		
		ts->idle_expires = expires;

		 if (unlikely(expires.tv64 == KTIME_MAX)) {
			if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
				hrtimer_cancel(&ts->sched_timer);
			goto out;
		}

		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
			hrtimer_start(&ts->sched_timer, expires,
				      HRTIMER_MODE_ABS_PINNED);
			
			if (hrtimer_active(&ts->sched_timer))
				goto out;
		} else if (!tick_program_event(expires, 0))
				goto out;
		tick_do_update_jiffies64(ktime_get());
	}
	raise_softirq_irqoff(TIMER_SOFTIRQ);
out:
	ts->next_jiffies = next_jiffies;
	ts->last_jiffies = last_jiffies;
}

//.........这里部分代码省略.........

	cpu = smp_processor_id();
	if (unlikely(local_softirq_pending()))
		printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
		       local_softirq_pending());

	now = ktime_get();
	/*
	 * When called from irq_exit we need to account the idle sleep time
	 * correctly.
	 */
	if (ts->tick_stopped) {
		delta = ktime_sub(now, ts->idle_entrytime);
		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
	}

	ts->idle_entrytime = now;
	ts->idle_calls++;

	/* Read jiffies and the time when jiffies were updated last */
	do {
		seq = read_seqbegin(&xtime_lock);
		last_update = last_jiffies_update;
		last_jiffies = jiffies;
	} while (read_seqretry(&xtime_lock, seq));

	/* Get the next timer wheel timer */
	next_jiffies = get_next_timer_interrupt(last_jiffies);
	delta_jiffies = next_jiffies - last_jiffies;

	if (rcu_needs_cpu(cpu))
		delta_jiffies = 1;
	/*
	 * Do not stop the tick, if we are only one off
	 * or if the cpu is required for rcu
	 */
	if (!ts->tick_stopped && delta_jiffies == 1)
		goto out;

	/* Schedule the tick, if we are at least one jiffie off */
	if ((long)delta_jiffies >= 1) {

		if (delta_jiffies > 1)
			cpu_set(cpu, nohz_cpu_mask);
		/*
		 * nohz_stop_sched_tick can be called several times before
		 * the nohz_restart_sched_tick is called. This happens when
		 * interrupts arrive which do not cause a reschedule. In the
		 * first call we save the current tick time, so we can restart
		 * the scheduler tick in nohz_restart_sched_tick.
		 */
		if (!ts->tick_stopped) {
			ts->idle_tick = ts->sched_timer.expires;
			ts->tick_stopped = 1;
			ts->idle_jiffies = last_jiffies;
		}

		/*
		 * If this cpu is the one which updates jiffies, then
		 * give up the assignment and let it be taken by the
		 * cpu which runs the tick timer next, which might be
		 * this cpu as well. If we don't drop this here the
		 * jiffies might be stale and do_timer() never
		 * invoked.
		 */
		if (cpu == tick_do_timer_cpu)
			tick_do_timer_cpu = -1;

		/*
		 * calculate the expiry time for the next timer wheel
		 * timer
		 */
		expires = ktime_add_ns(last_update, tick_period.tv64 *
				       delta_jiffies);
		ts->idle_expires = expires;
		ts->idle_sleeps++;

		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
			hrtimer_start(&ts->sched_timer, expires,
				      HRTIMER_MODE_ABS);
			/* Check, if the timer was already in the past */
			if (hrtimer_active(&ts->sched_timer))
				goto out;
		} else if(!tick_program_event(expires, 0))
				goto out;
		/*
		 * We are past the event already. So we crossed a
		 * jiffie boundary. Update jiffies and raise the
		 * softirq.
		 */
		tick_do_update_jiffies64(ktime_get());
		cpu_clear(cpu, nohz_cpu_mask);
	}
	raise_softirq_irqoff(TIMER_SOFTIRQ);
out:
	ts->next_jiffies = next_jiffies;
	ts->last_jiffies = last_jiffies;
end:
	local_irq_restore(flags);
}