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cpu的调度域可以分为下面3类。目前arm都是用的mcstatic struct sched_domain_topology_level default_topology[] = {#ifdef CONFIG_SCHED_SMT	{ cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },#endif#ifdef CONFIG_SCHED_MC	{ cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },#endif	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },	{ NULL, },};static struct sched_domain_topology_level *sched_domain_topology =	default_topology;在下面的函数中都cpu的域进行初始化可以看到域的初始化分为4部分static intbuild_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *attr){	enum s_alloc alloc_state;	struct sched_domain *sd;	struct s_data d;	struct rq *rq = NULL;	int i, ret = -ENOMEM;	alloc_state = __visit_domain_allocation_hell(&d, cpu_map);	if (alloc_state != sa_rootdomain)		goto error;	/* Set up domains for CPUs specified by the cpu_map: */	#针对cpu_map中的cpu 来是指cpu domain	for_each_cpu(i, cpu_map) {		struct sched_domain_topology_level *tl;		sd = NULL;		for_each_sd_topology(tl) {			#为每个cpubuild 调度域			sd = build_sched_domain(tl, cpu_map, attr, sd, i);			#正常情况下sched_domain_topology应该等于default_topology，这里每个cpu设置调度域			if (tl == sched_domain_topology)				*per_cpu_ptr(d.sd, i) = sd;			if (tl->flags & SDTL_OVERLAP)				sd->flags |= SD_OVERLAP;			#cpu_map中每个cpu 都是指调度域后，退出这个for循环			if (cpumask_equal(cpu_map, sched_domain_span(sd)))				break;		}	}	/* Build the groups for the domains */	#为每个cpu 设置group	for_each_cpu(i, cpu_map) {		for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {			sd->span_weight = cpumask_weight(sched_domain_span(sd));			if (sd->flags & SD_OVERLAP) {				if (build_overlap_sched_groups(sd, i))					goto error;			} else {			#主要是设置sd->group				if (build_sched_groups(sd, i))					goto error;			}		}	}#从上面可知每个cpu都有一个domain->groups	/* Calculate CPU capacity for physical packages and nodes */	for (i = nr_cpumask_bits-1; i >= 0; i--) {		if (!cpumask_test_cpu(i, cpu_map))			continue;		for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {			claim_allocations(i, sd);			#设置调度域中group中的每个cpu的能力			init_sched_groups_capacity(i, sd);		}	}#下面为么个rq attach domain	/* Attach the domains */	rcu_read_lock();	for_each_cpu(i, cpu_map) {	#得到每个cpu的running queue		rq = cpu_rq(i);		#每个cpu的调度域		sd = *per_cpu_ptr(d.sd, i);		/* Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing: */		#如rq中表示cpucapacity的值大于调度域中表示cpu capacity，则更新调度域中的cpu的capacity		if (rq->cpu_capacity_orig > READ_ONCE(d.rd->max_cpu_capacity))			WRITE_ONCE(d.rd->max_cpu_capacity, rq->cpu_capacity_orig);		#将sd 作为cpu的base domain		cpu_attach_domain(sd, d.rd, i);	}	rcu_read_unlock();	#用于debug是显示cpu的最大的capacity	if (rq && sched_debug_enabled) {		pr_info("span: %*pbl (max cpu_capacity = %lu)\n",			cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);	}	ret = 0;error:	__free_domain_allocs(&d, alloc_state, cpu_map);	return ret;}

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