Linux5.4 Qcom平臺

1. per-cpu的 update_util_data 例項是排程器與schedutil調頻驅動溝通的橋樑，cpufreq_update_util()函式中訪問裡面的回撥函式進行調頻。

2. 觸發調頻的時機

(1) enqueue_task_fair 時

activate_task
move_queued_task
do_set_cpus_allowed
rt_mutex_setprio
set_user_nice
__sched_setscheduler
sched_setnuma
sched_move_task
enqueue_task_core
    enqueue_task 
 
--> enqueue_task_fair --> if (p->in_iowait) cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);

(2) pick_next_task_fair時

balance_fair
pick_next_task_fair
    newidle_balance --> nohz_newidle_balance --> _nohz_idle_balance --> rebalance_domains --> load_balance --> find_busiest_group --> update_sd_lb_stats --> update_sg_lb_stats --> update_nohz_stats --> update_blocked_averages --> cpufreq_update_util(rq, 0
 
);
    newidle_balance --> nohz_newidle_balance --> _nohz_idle_balance --> update_nohz_stats --> update_blocked_averages --> cpufreq_update_util(rq, 0);
    newidle_balance --> load_balance --> find_busiest_group --> update_sd_lb_stats --> update_sg_lb_stats --> update_nohz_stats --> update_blocked_averages --> cpufreq_update_util(rq, 0
 
);

(3) scheduler_tick時

scheduler_tick() --> trigger_load_balance //只有在 scheduler_tick()中通過 SCHED_SOFTIRQ 觸發負載均衡。
__init init_sched_fair_class --> open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);
trigger_load_balance --> raise_softirq(SCHED_SOFTIRQ);
    run_rebalance_domains --> nohz_idle_balance --> _nohz_idle_balance --> update_nohz_stats --> update_blocked_averages --> cpufreq_update_util(rq, 0);
    run_rebalance_domains --> nohz_idle_balance --> _nohz_idle_balance --> rebalance_domains --> load_balance --> find_busiest_group --> update_sd_lb_stats --> update_sg_lb_stats --> update_nohz_stats --> update_blocked_averages --> cpufreq_update_util(rq, 0);
    run_rebalance_domains --> update_blocked_averages --> cpufreq_update_util(rq, 0);
    run_rebalance_domains --> rebalance_domains --> load_balance --> find_busiest_group --> update_sd_lb_stats --> update_sg_lb_stats --> update_nohz_stats --> update_blocked_averages --> cpufreq_update_util(rq, 0);

(4) switched_to回撥

switched_to_fair --> attach_task_cfs_rq --> attach_entity_cfs_rq --> attach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(5) task_change_group回撥

task_change_group_fair --> task_move_group_fair --> attach_task_cfs_rq --> attach_entity_cfs_rq --> attach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(6) 喚醒程序時

各種鎖，程序間通訊機制呼叫wake_up_q
_do_fork
    wake_up_new_task --> post_init_entity_util_avg --> attach_entity_cfs_rq --> attach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(7) sched_online_group呼叫時

sched_online_group --> online_fair_sched_group --> attach_entity_cfs_rq --> attach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(8) migrate_task_rq回撥時

migrate_task_rq_fair --> detach_entity_cfs_rq --> detach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(9) switched_from回撥時

switched_from_fair --> detach_task_cfs_rq --> detach_entity_cfs_rq --> detach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(10) switched_to回撥時

switched_to_fair --> detach_task_cfs_rq --> detach_entity_cfs_rq --> detach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(11) 往rq中新增/移除任務時

enqueue_entity
dequeue_entity
set_next_entity
put_prev_entity
entity_tick
enqueue_task_fair
dequeue_task_fair
__update_blocked_fair
propagate_entity_cfs_rq
detach_entity_cfs_rq
attach_entity_cfs_rq
sched_group_set_shares
    update_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)
    update_load_avg --> attach_entity_load_avg --> cfs_rq_util_change(cfs_rq, flags) --> cpufreq_update_util(rq, flags)

(12) scheduler_tick 中直接呼叫調頻

scheduler_tick --> cpufreq_update_util

3. 以排程節拍為例介紹調頻

(1) 呼叫路徑

時鐘中斷 --> scheduler_tick --> curr->sched_class->task_tick(CFS：task_tick_fair) --> entity_tick --> update_load_avg --> cfs_rq_util_change --> cpufreq_update_util(rq, flags)

(2) cpufreq_update_util(rq, flags)被Qcom更改為只接受flag中設定SCHED_CPUFREQ_WALT標誌的調頻了。

static inline void cpufreq_update_util(struct rq *rq, unsigned int flags)
{
    struct update_util_data *data;
    u64 clock;

#ifdef CONFIG_SCHED_WALT
    if (!(flags & SCHED_CPUFREQ_WALT)) /*變成只接受設定有WALT標誌位的調頻*/
        return;
    clock = sched_ktime_clock();
#else
    clock = rq_clock(rq);
#endif

    data = rcu_dereference_sched(*per_cpu_ptr(&cpufreq_update_util_data, cpu_of(rq)));
    if (data)
        data->func(data, clock, flags);
}

(3) cpufreq_update_util(rq, flags) 中flags支援的調頻標誌位

//include\linux\sched\cpufreq.h
#define SCHED_CPUFREQ_IOWAIT            (1U << 0)
#define SCHED_CPUFREQ_MIGRATION            (1U << 1)
#define SCHED_CPUFREQ_INTERCLUSTER_MIG    (1U << 3)
#define SCHED_CPUFREQ_WALT                (1U << 4)
#define SCHED_CPUFREQ_PL                (1U << 5)
#define SCHED_CPUFREQ_EARLY_DET            (1U << 6)
#define SCHED_CPUFREQ_CONTINUE            (1U << 8)

4. cpufreq還與thermal的cooldown有關聯

struct cpufreq_policy {
    ...
    struct thermal_cooling_device *cdev
};

5. governor/driver/policy分別是

# cat /sys/devices/system/cpu/cpufreq/policy0/scaling_driver  //driver
qcom-cpufreq-hw
# cat /sys/devices/system/cpu/cpufreq/policy0/scaling_governor //governor
schedutil
# ls /sys/devices/system/cpu/cpufreq/policy0/schedutil //policy
above_hispeed_delay  down_rate_limit_us  hispeed_freq  hispeed_load  pl  rtg_boost_freq  target_loads  up_rate_limit_us