【内核调度、负载均衡】【detach_tasks】

最新推荐文章于 2024-10-30 15:43:13 发布

原创

最新推荐文章于 2024-10-30 15:43:13 发布 · 1.1k 阅读

2 ·

CC 4.0 BY-SA版权

detach_tasks

在load balance中会将busiest cpu上的task detach掉，然后atach在local cpu上。返回值为detach的task的数量

/*
 * detach_tasks() -- tries to detach up to imbalance weighted load from
 * busiest_rq, as part of a balancing operation(操作) within domain "sd".
 *
 * Returns number of detached tasks if successful and 0 otherwise.
 */
 // 返回值为detach的task的数量
static int detach_tasks(struct lb_env *env, struct rq_flags *rf)
{
	//src_rq是busiest的rq
	struct list_head *tasks = &env->src_rq->cfs_tasks;
	struct task_struct *p;
	unsigned long load;
	int detached = 0;

	lockdep_assert_held(&env->src_rq->lock);

	if (env->imbalance <= 0)
		return 0;
	/* (7.6.1) 遍历busiest rq中的进程 */
	while (!list_empty(tasks)) {
		/*
		 * We don't want to steal all, otherwise we may be treated likewise,
		 * which could at worst lead to a livelock crash.
		 */
		 /* (7.6.2) 如果dest cpu不是idle，不能将busiest cpu迁移到idle状态 */  
		if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
			break;

		p = list_first_entry(tasks, struct task_struct, se.group_node);

		env->loop++;
		/* We've more or less seen every task there is, call it quits */
		/* (7.6.3) 遍历任务最多不超过sysctl_sched_nr_migrate(32) */
		if (env->loop > env->loop_max)
			break;

		/* take a breather every nr_migrate tasks */
		/* (7.6.4) 每sched_nr_migrate_break个任务遍历需要跳出休息一下，
         如果没有达到env->loop_max，后面会重来*/
		if (env->loop > env->loop_break) {
			env->loop_break += sched_nr_migrate_break;
			env->flags |= LBF_NEED_BREAK;
			break;
		}
		/* (7.6.5) 判断任务是否支持迁移？ */
		if (!can_migrate_task(p, env))
			goto next;
		/* (7.6.6) 获取p进程相对顶层cfs_rq的负载， 
					根据负载判断进程是否适合迁移*/
		load = task_h_load(p);
		// LB_MIN 定义的是false
		if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
			goto next;

		if ((load / 2) > env->imbalance)
			goto next;
		// 把task加到env的list里面
		detach_task(p, env, rf);
		list_add(&p->se.group_node, &env->tasks);

		detached++;
		env->imbalance -= load;

#ifdef CONFIG_PREEMPT
		/*
		 * NEWIDLE balancing is a sourc