find_busiest_group

enum group_type {
   group_other = 0,
   group_misfit_task,
   group_imbalanced,
   group_overloaded,
};

/*** find_busiest_group - Returns the busiest group within the sched_domain* if there is an imbalance(不平衡).** Also calculates the amount of weighted load which should be moved* to restore(恢复) balance.** @env: The load balancing environment.** Return:  - The busiest group if imbalance exists.*/
static struct sched_group *find_busiest_group(struct lb_env *env)
{struct sg_lb_stats *local, *busiest;struct sd_lb_stats sds;init_sd_lb_stats(&sds);/** Compute the various statistics relavent for load balancing at* this level.*//* (7.3.1) 更新本层级sched_group链表中，每个sched_group的负载,并选出busiest的一个sched_group*/update_sd_lb_stats(env, &sds);/* (7.3.2) 如果EAS使能，跨cluster的任务迁移使用EAS来做 */if (energy_aware() && !sd_overutilized(env->sd) &&!env->sd->parent)goto out_balanced;local = &sds.local_stat;busiest = &sds.busiest_stat;/* ASYM feature bypasses nice load balance check */
//ASYM功能绕过了不错的负载平衡检查if (check_asym_packing(env, &sds))return sds.busiest;/* There is no busy sibling group to pull tasks from *//* (7.3.4) busiest sg上没有负载，返回空 */if (!sds.busiest || busiest->sum_nr_running == 0)goto out_balanced;/* XXX broken for overlapping NUMA groups *//* (7.3.5) sg链表里的平均负载 */sds.avg_load = (SCHED_CAPACITY_SCALE * sds.total_load)/ sds.total_capacity;/** If the busiest group is imbalanced the below checks don't* work because they assume all things are equal, which typically* isn't true due to cpus_allowed constraints and the like.*//* (7.3.6) 如果busiest sg低一级别的因为cpu affinity没有balance成功，设置了group_imbalanced标志 强制在当前级别上进行balance*/if (busiest->group_type == group_imbalanced)goto force_balance;/** When dst_cpu is idle, prevent SMP nice and/or asymmetric group* capacities from resulting in underutilization due to avg_load.*//* (7.3.7) 如果dest cpu/group很闲，busiest负载很重，  强制开展balance*/if (env->idle != CPU_NOT_IDLE && group_has_capacity(env, local) &&busiest->group_no_capacity)goto force_balance;/* Misfit tasks should be dealt with regardless of the avg load */if (busiest->group_type == group_misfit_task)goto force_balance;/** If the local group is busier than the selected busiest group* don't try and pull any tasks.*//* (7.3.8)  如果dest_cpu所在sg的负载都大于busiest sg的负载，放弃balance*/if (local->avg_load >= busiest->avg_load)goto out_balanced;/** Don't pull any tasks if this group is already above the domain* average load.*/if (local->avg_load >= sds.avg_load)goto out_balanced;if (env->idle == CPU_IDLE) {/** This cpu is idle. If the busiest group is not overloaded* and there is no imbalance between this and busiest group* wrt idle cpus, it is balanced. The imbalance becomes* significant if the diff is greater than 1 otherwise we* might end up to just move the imbalance on another group*/if ((busiest->group_type != group_overloaded) &&(local->idle_cpus <= (busiest->idle_cpus + 1)))goto out_balanced;} else {/** In the CPU_NEWLY_IDLE, CPU_NOT_IDLE cases, use* imbalance_pct to be conservative.*/if (100 * busiest->avg_load <=env->sd->imbalance_pct * local->avg_load)goto out_balanced;}force_balance:/* Looks like there is an imbalance. Compute it */env->src_grp_type = busiest->group_type;calculate_imbalance(env, &sds);//也去计算需要迁移的负载量return env->imbalance ? sds.busiest : NULL;out_balanced:env->imbalance = 0;return NULL;
}

init_sd_lb_stats(&sds)详见

https://blog.csdn.net/feifei_csdn/article/details/107160808

update_sd_lb_stats(env, &sds);详见

https://blog.csdn.net/feifei_csdn/article/details/107317450

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【内核调度、负载均衡】【find_busiest_group】

find_busiest_group

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