【内核调度、负载计算】【WALT】【walt_update_task_ravg】

walt_update_task_ravg在scheduler_tick中进行更新，即会周期性的更新

walt_update_task_ravg

/* Reflect task activity on its demand and cpu's busy time statistics */
void walt_update_task_ravg(struct task_struct *p, struct rq *rq,
	     int event, u64 wallclock, u64 irqtime)
{
	u64 old_window_start;

	if (walt_disabled || !rq->window_start)
		return;

	lockdep_assert_held(&rq->lock);

	old_window_start = update_window_start(rq, wallclock);

	if (!p->ravg.mark_start)
		goto done;

	update_task_demand(p, rq, event, wallclock);
	update_cpu_busy_time(p, rq, event, wallclock, irqtime);

done:
	if (rq->window_start > old_window_start) {
		unsigned long cap_orig = capacity_orig_of(cpu_of(rq));
		unsigned int busy_limit =
			(walt_ravg_window * walt_busy_threshold) / 100;

		// walt_ravg_window  12ms
        // walt_busy_threshold 75 繁忙的阈值
		busy_limit = (busy_limit * cap_orig) >> SCHED_CAPACITY_SHIFT;
		if (rq->prev_runnable_sum >= busy_limit) {
			if (rq->is_busy == CPU_BUSY_CLR)
				rq->is_busy = CPU_BUSY_PREPARE;
			else if (rq->is_busy == CPU_BUSY_PREPARE)
				rq->is_busy = CPU_BUSY_SET;
		} else if (rq->is_busy != CPU_BUSY_CLR) {
			rq->is_busy = CPU_BUSY_CLR;
		}
	}

	trace_walt_update_task_ravg(p, rq, event, wallclock, irqtime);

	p->ravg.mark_start = wallclock;
}

update_task_demand详见

https://blog.youkuaiyun.com/feifei_csdn/article/details/107407248

update_cpu_busy_time详见

https://blog.youkuaiyun.com/feifei_csdn/article/details/107457728

update_window_start

__read_mostly unsigned int walt_ravg_window = (12000000 / TICK_NSEC) * TICK_NSEC;

表示12s

rq->window_start	rq->window_start += (u64)nr_windows * (u64)walt_ravg_window;
rq->cum_window_demand	rq->cum_window_demand = rq->cumulative_runnable_avg

static u64
update_window_start(struct rq *rq, u64 wallclock)
{
	s64 delta;
	int nr_windows;
	u64 old_window_start = rq->window_start;

	delta = wallclock - rq->window_start;
	/* If the MPM global timer is cleared, set delta as 0 to avoid kernel BUG happening */
	if (delta < 0) {
		delta = 0;
		WARN_ONCE(1, "WALT wallclock appears to have gone backwards or reset\n");
	}

	if (delta < walt_ravg_window)
		return old_window_start;

	nr_windows = div64_u64(delta, walt_ravg_window);
	rq->window_start += (u64)nr_windows * (u64)walt_ravg_window;

	rq->cum_window_demand = rq->cumulative_runnable_avg;

	return old_window_start;
}

walt_set_window_start

这里可以看看他的初始化，这个函数在scheduler_tick中进行更新

void walt_set_window_start(struct rq *rq, struct rq_flags *rf)
{
	if (likely(rq->window_start))
		return;

	if (cpu_of(rq) == sync_cpu) {
		rq->window_start = 1;
	} else {
		struct rq *sync_rq = cpu_rq(sync_cpu);
		rq_unpin_lock(rq, rf);
		double_lock_balance(rq, sync_rq);
		rq->window_start = sync_rq->window_start;
		rq->curr_runnable_sum = rq->prev_runnable_sum = 0;
		raw_spin_unlock(&sync_rq->lock);
		rq_repin_lock(rq, rf);
	}

	rq->curr->ravg.mark_start = rq->window_start;
}