【内核调度、负载均衡】【update_sd_lb_stats】

最新推荐文章于 2023-10-12 15:42:55 发布

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最新推荐文章于 2023-10-12 15:42:55 发布

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分类专栏： linux内核

本文链接：https://blog.youkuaiyun.com/feifei_csdn/article/details/107317450

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本文深入探讨了Linux内核中的调度域（sched_domain）负载平衡机制，详细解析了get_sd_load_idx函数如何根据CPU状态获取负载指数，以及update_sd_lb_stats函数如何更新调度域的统计信息以实现负载平衡。此外，还介绍了set_sd_overutilized和clear_sd_overutilized函数的作用，以及如何通过update_sg_lb_stats计算调度组负载统计。

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get_sd_load_idx

这里面涉及到了一个unsigned long cpu_load[CPU_LOAD_IDX_MAX];数组。scheduler会更具不同的load balance类型（busy，newly idle，idle)选择不同的load进行计算，主要是在update_sg_lb_stats时进行计算

/**
 * get_sd_load_idx - Obtain the load index for a given sched domain.
 * @sd: The sched_domain whose load_idx is to be obtained.
 * @idle: The idle status of the CPU for whose sd load_idx is obtained.
 *
 * Return: The load index.
 */
static inline int get_sd_load_idx(struct sched_domain *sd,
					enum cpu_idle_type idle)
{
	int load_idx;

	switch (idle) {
	case CPU_NOT_IDLE:
		load_idx = sd->busy_idx;
		break;

	case CPU_NEWLY_IDLE:
		load_idx = sd->newidle_idx;
		break;
	default:
		load_idx = sd->idle_idx;
		break;
	}

	return load_idx;
}

set_sd_overutilized&clear_sd_overutilized

static void set_sd_overutilized(struct sched_domain *sd)
{
	trace_sched_overutilized(sd, sd->shared->overutilized, true);
	sd->shared->overutilized = true;
}

static void clear_sd_overutilized(struct sched_domain *sd)
{
	trace_sched_overutilized(sd, sd->shared->overutilized, false);
	sd->shared->overutilized = false;
}

update_sd_lb_stats

update_blocked_averages实际上可以视为更新cpu上entity的load和cpu的load值，详见

https://blog.youkuaiyun.com/feifei_csdn/article/details/107332155

/**
 * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
 * @env: The load balancing environment.
 * @sds: variable to hold the statistics for this sched_domain.
 */
static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
{
	struct sched_domain *child = env->sd->child;
	struct sched_group *sg = env->sd->groups;
	struct sg_lb_stats *local = &sds->local_stat;
	struct sg_lb_stats tmp_sgs;
	int load_idx;
	bool overload = false, overutilized = false, misfit_task = false;
	bool prefer_sibling = child && child->flags & SD_PREFER_SIBLING;

#ifdef CONFIG_NO_HZ_COMMON//一般配置的都是true
	if (env->idle == CPU_NEWLY_IDLE) {
		int cpu;

		/* Update the stats of NOHZ idle CPUs in the sd */
		for_each_cpu_and(cpu, sched_domain_span(env->sd),
				 nohz.idle_cpus_mask) {
			struct rq *rq = cpu_rq(cpu);

			/* ... Unless we've already done since the last tick */
            // a在b的后面
			if (time_after(jiffies, rq->last_blocked_load_update_tick))
				update_blocked_averages(cpu);
		}
	}
	/*
	 * If we've just updated all of the NOHZ idle CPUs, then we can push
	 * back the next nohz.next_update, which will prevent an unnecessary
	 * wakeup for the nohz stats kick
	 */
	if (cpumask_subset(nohz.idle_cpus_mask, sched_domain_span(env->sd)))
		nohz.next_update = jiffies + LOAD_AVG_PERIOD;
#endif
	//load_idx 实际上在sd的rq->cpu_load[load_idx-1]
	load_idx = get_sd_load_idx(env->sd, env->idle);
	/* (7.3.1.2) 逐个轮询本层级sched_group链表中的每个sched_group */
	do {
		struct sg_lb_stats *sgs = &tmp_sgs;
		int local_group;
		/* (7.3.1.3) 如果sg是当前cpu所在的sg，则本sg称为local_group

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