【内核调度、负载均衡】【find_busiest_queue】

在最繁忙的group中去寻找最繁忙的cpu

find_busiest_queue

/*
 * find_busiest_queue - find the busiest runqueue among the cpus in group.
 */
 //冒泡排序找到group内最忙的rq
static struct rq *find_busiest_queue(struct lb_env *env,
				     struct sched_group *group)
{
	struct rq *busiest = NULL, *rq;
	unsigned long busiest_load = 0, busiest_capacity = 1;
	int i;
	
	//冒泡排序遍历group内最忙的cpu
	for_each_cpu_and(i, sched_group_span(group), env->cpus) {
		unsigned long capacity, wl;
		enum fbq_type rt;

		rq = cpu_rq(i);
		rt = fbq_classify_rq(rq);

		/*
		 * We classify groups/runqueues into three groups:
		 *  - regular: there are !numa tasks
		 *  - remote:  there are numa tasks that run on the 'wrong' node
		 *  - all:     there is no distinction
		 *
		 * In order to avoid migrating ideally placed numa tasks,
		 * ignore those when there's better options.
		 *
		 * If we ignore the actual busiest queue to migrate another
		 * task, the next balance pass can still reduce the busiest
		 * queue by moving tasks around inside the node.
		 *
		 * If we cannot move enough load due to this classification
		 * the next pass will adjust the group classification and
		 * allow migration of more tasks.
		 *
		 * Both cases only affect the total convergence complexity.
		 */
		if (rt > env->fbq_type)
			continue;

		/*
		 * For ASYM_CPUCAPACITY domains with misfit(错配) tasks we simply
		 * seek the "biggest" misfit task.
		 */
		if (env->src_grp_type == group_misfit_task) {
			if (rq->misfit_task_load > busiest_load) {
				busiest_load = rq->misfit_task_load;
				busiest = rq;
			}
			continue;
		}

		capacity = capacity_of(i);

		/*
		 * For ASYM_CPUCAPACITY domains, don't pick a cpu that could
		 * eventually lead to active_balancing high->low capacity.
		 * Higher per-cpu capacity is considered better than balancing
		 * average load.
		 */
		if (env->sd->flags & SD_ASYM_CPUCAPACITY &&
		    capacity_of(env->dst_cpu) < capacity &&
		    rq->nr_running == 1)
			continue;

		wl = weighted_cpuload(rq);

		/*
		 * When comparing with imbalance, use weighted_cpuload()
		 * which is not scaled with the cpu capacity.
		 */

		if (rq->nr_running == 1 && wl > env->imbalance &&
		    !check_cpu_capacity(rq, env->sd))
			continue;

		/*
		 * For the load comparisons with the other cpu's, consider
		 * the weighted_cpuload() scaled with the cpu capacity, so
		 * that the load can be moved away from the cpu that is
		 * potentially running at a lower capacity.
		 *
		 * Thus we're looking for max(wl_i / capacity_i), crosswise
		 * multiplication to rid ourselves of the division works out
		 * to: wl_i * capacity_j > wl_j * capacity_i;  where j is
		 * our previous maximum.
		 */
		if (wl * busiest_capacity > busiest_load * capacity) {
			busiest_load = wl;
			busiest_capacity = capacity;
			busiest = rq;
		}
	}

	return busiest;
}

当时我为什么会去画这个图呢？感觉是没有必要的，去绘制C语言的函数的流程图。