AOSP Kernel4.14已經有這個feature，kernel4.20參考AOSP kernel也支持這個feature：
e1799a8 sched/topology, arch/arm: Rebuild sched_domain hierarchy when CPU capacity changes
3ba09df sched/topology, arch/arm64: Rebuild the sched_domain hierarchy when the CPU capacity changes
bb1fbdd sched/topology, drivers/base/arch_topology: Rebuild the sched_domain hierarchy when capacities change
05484e0 sched/topology: Add SD_ASYM_CPUCAPACITY flag detection
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數據結構
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sched_domain的建立
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函數調用關係
|rebuild_sched_domains() /*kernel/cgroup/cpuset.c*/ (1) |update_cpumasks_hier() |update_relax_domain_level() |update_flag() |update_prstate() /*(kernel5.4)*/ \-|rebuild_sched_domains_locked(void) | |\-|partition_sched_domains_locked() /*kernel4.14/kernel/sched/topology.c*/ | \-|build_sched_domains() | \-|generate_sched_domains(&doms, &attr) /*kernel5.4/kernel/cgroup/cpuset.c*/ |partition_and_rebuild_sched_domains() | \-|partition_sched_domains_locked() /*kernel5.4/kernel/sched/topology.c*/ | \-|build_sched_domains() | |rebuild_root_domains() |cpuhp_hp_states[CPUHP_AP_ACTIVE] /*kernel/cpu.c*/ (2) | \-|sched_cpu_activate() /*kernel/sched/core.c*/ |sched_cpu_deactivate() \-|cpuset_cpu_active(1, NULL, NULL) |cpuset_cpu_inactive(1, NULL, NULL) | \-|partition_sched_domains() /*kernel/sched/topology.c*/ | \partition_sched_domains_locked \-|build_sched_domains() |__init sched_init_smp(void) /*kernel/sched/core.c*/ (3) | \-|sched_init_domains(cpu_active_mask) /*kernel/sched/topology.c*/ \-|build_sched_domains()(3) 系統初始化時爲所有 cpu_active_mask cpu(排除housekeeping HK_FLAG_DOMAIN)建立一個sched domain.
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關鍵函數
build_sched_domains() |__visit_domain_allocation_hell() | |__sdt_alloc() | |alloc_rootdomain() | |init_rootdomain() | |init_irq_work() | |init_dl_bw() | |cpudl_init() | |cpupri_init() | |init_max_cpu_capacity() | |build_sched_domain() | |sd_init() | |build_sched_groups() | |get_group() | |init_sched_groups_capacity()
1427 * Topology list, bottom-up.
1428 */
1429 static struct sched_domain_topology_level default_topology[] = {
1430 #ifdef CONFIG_SCHED_SMT
1431 { cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
1432 #endif
1433 #ifdef CONFIG_SCHED_MC
1434 { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
1435 #endif
1436 { cpu_cpu_mask, SD_INIT_NAME(DIE) },
1437 { NULL, },
1438 };
1978 static int
1979 build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *attr)
1980 {
1981 enum s_alloc alloc_state = sa_none;
1982 struct sched_domain *sd;
1983 struct s_data d;
1984 int i, ret = -ENOMEM;
1985 struct sched_domain_topology_level *tl_asym;
1986 bool has_asym = false;
1990
1991 alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
1994
1995 tl_asym = asym_cpu_capacity_level(cpu_map); /*commit:05484e09*/ (1)
1996
1997 /* Set up domains for CPUs specified by the cpu_map: */
1998 for_each_cpu(i, cpu_map) { /*loop每個cpu*/ (2)
1999 struct sched_domain_topology_level *tl;
2000
2001 sd = NULL;
2002 for_each_sd_topology(tl) { /*loop每個topology level*/ (3)
2003 int dflags = 0;
2004
2005 if (tl == tl_asym) {
2006 dflags |= SD_ASYM_CPUCAPACITY; /*設置異構topology level sched domain的flag*/ （4）
2007 has_asym = true;
2008 }
2009
2010 if (WARN_ON(!topology_span_sane(tl, cpu_map, i)))
2011 goto error;
2012
/*初始化cpu i所在的tl(mc or die)的sched domain*/ (5)
2013 sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i);
2014
2015 if (tl == sched_domain_topology)
/*初始化s_data->sd，爲每個cpu的最低level的sched domain*/ (6)
2016 *per_cpu_ptr(d.sd, i) = sd;
2017 if (tl->flags & SDTL_OVERLAP)
2018 sd->flags |= SD_OVERLAP;
2019 if (cpumask_equal(cpu_map, sched_domain_span(sd)))
2020 break;
2021 }
2022 }
2023
2024 /* Build the groups for the domains */ （7）
2025 for_each_cpu(i, cpu_map) {
2026 for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
2027 sd->span_weight = cpumask_weight(sched_domain_span(sd));
2028 if (sd->flags & SD_OVERLAP) {
2029 if (build_overlap_sched_groups(sd, i))
2030 goto error;
2031 } else {
2032 if (build_sched_groups(sd, i))
2033 goto error;
2034 }
2035 }
2036 }
2037
2038 /* Calculate CPU capacity for physical packages and nodes */ （8）
2039 for (i = nr_cpumask_bits-1; i >= 0; i--) {
2040 if (!cpumask_test_cpu(i, cpu_map))
2041 continue;
2042
2043 for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
2044 claim_allocations(i, sd);
2045 init_sched_groups_capacity(i, sd);
2046 }
2047 }
2048
2049 /* Attach the domains */ （9）
2050 rcu_read_lock();
2051 for_each_cpu(i, cpu_map) {
2052 sd = *per_cpu_ptr(d.sd, i);
2053 cpu_attach_domain(sd, d.rd, i);
2054 }
2055 rcu_read_unlock();
2056
2057 if (has_asym)
2058 static_branch_inc_cpuslocked(&sched_asym_cpucapacity);
2059
2060 ret = 0;
2061 error:
2062 __free_domain_allocs(&d, alloc_state, cpu_map);
2063
2064 return ret;
2065 }
(1) loop cpu異構的domain level，在不支持smt的四大四小架構中，只有MC domain和DIE domain，此時返回DIE domain
(2)(3) loop cpu0->MC, cpu0->DIE, cpu1->MC, cpu1->DIE.....
(4) DIE domain包含cluster0和cluster1兩種架構cpu，SD_ASYM_CPUCAPACITY被置位；MC domain 都是同構cpu，SD_ASYM_CPUCAPACITY不置位。
(5) build sched domain關鍵函數
(6) 初始化s_data->sd爲cpu0～cpu7的MC domain
(7) loop cpu0~7的 s_data->sd（都爲MC domain）及其parent（DIE domain），具體是：cpu0->MC,cpu0->DIE,cpu1->MC,cpu1->DIE......分別對loop到的domain build sched group
1113 * build_sched_groups will build a circular linked list of the groups
1114 * covered by the given span, will set each group's ->cpumask correctly,
1115 * and will initialize their ->sgc.
1116 *
1117 * Assumes the sched_domain tree is fully constructed
1118 */
/*指定cpu i和sched domain，建立sched group。
cpu0->MC,cpu0->DIE,cpu1->MC,cpu1->DIE......*/
1119 static int
1120 build_sched_groups(struct sched_domain *sd, int cpu)
1121 {
1122 struct sched_group *first = NULL, *last = NULL;
1123 struct sd_data *sdd = sd->private;
1124 const struct cpumask *span = sched_domain_span(sd);
1125 struct cpumask *covered;
1126 int i;
1127
1128 lockdep_assert_held(&sched_domains_mutex);
1129 covered = sched_domains_tmpmask;
1130
1131 cpumask_clear(covered);
1132
/*從i從cpu開始，在span mask範圍內loop*/
1133 for_each_cpu_wrap(i, span, cpu) {
1134 struct sched_group *sg;
1135
1136 if (cpumask_test_cpu(i, covered))
1137 continue;
1138
1139 sg = get_group(i, sdd);
1140
1141 cpumask_or(covered, covered, sched_group_span(sg));
1142
1143 if (!first)
1144 first = sg;
1145 if (last)
1146 last->next = sg;
1147 last = sg;
1148 }
1149 last->next = first;
1150 sd->groups = first;
1151
1152 return 0;
1153 }
1075 static struct sched_group *get_group(int cpu, struct sd_data *sdd)
1076 {
1077 struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
1078 struct sched_domain *child = sd->child;
1079 struct sched_group *sg;
1080 bool already_visited;
1081
1082 if (child)
/*如果這個domain（DIE domain）包含child，取此cpu DIE domain對應的child domain的cpu mask
的第一個cpu number；所以cpu0~3對應的cpu=0，cpu4~7對應的cpu=4*/
1083 cpu = cpumask_first(sched_domain_span(child));
1084
1085 sg = *per_cpu_ptr(sdd->sg, cpu);
/*建立sd_data中sg和sgc的關係。如果是DIE topology level，只包含兩個group，分別對應
cpu0（cpu0~3）和cpu4（cpu4~7）；如果是MC topology level，包含8個，每個cpu MC domain對應
一個group*/
1086 sg->sgc = *per_cpu_ptr(sdd->sgc, cpu);
1087
1088 /* Increase refcounts for claim_allocations: */
1089 already_visited = atomic_inc_return(&sg->ref) > 1;
1090 /* sgc visits should follow a similar trend as sg */
1091 WARN_ON(already_visited != (atomic_inc_return(&sg->sgc->ref) > 1));
1092
1093 /* If we have already visited that group, it's already initialized. */
1094 if (already_visited)
1095 return sg;
1096
/*如果是包含child的DIE domain，初始化sg->cpumask=(child)sd->span(0x0F,0xF0),
初始化sg->sgc->cpumask=sg->cpumask*/
1097 if (child) {
1098 cpumask_copy(sched_group_span(sg), sched_domain_span(child));
1099 cpumask_copy(group_balance_mask(sg), sched_group_span(sg));
1100 } else { /*如果是MC domain，分別添加當前cpu到sg->cpumask和sg->sgc->cpumask*/
1101 cpumask_set_cpu(cpu, sched_group_span(sg));
1102 cpumask_set_cpu(cpu, group_balance_mask(sg));
1103 }
1104
/*根據組權重初始化sgc capacicy，MC level的每個group只包含一個cpu，權重=1；
DIE level的兩個group分別包含cpu0~3和cpu4~7，組權重=4*/
1105 sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sched_group_span(sg));
1106 sg->sgc->min_capacity = SCHED_CAPACITY_SCALE;
1107 sg->sgc->max_capacity = SCHED_CAPACITY_SCALE;
1108
1109 return sg;
1110 }