smp_init过程解析

当你看到这样的log，会不会很慌张？

竟然由CPU没有启动成功，除了什么故障？

本文将结合我遇到的一个问题，将启动过程中bringup secondary cpu的过程分析一下。

smp_init代码如下：

602 void __init smp_init(void)
603 {
604     int num_nodes, num_cpus;
605     unsigned int cpu;
606 
607     idle_threads_init();
608     cpuhp_threads_init();
609 
610     pr_info("====cpuhp-walk:Bringing up secondary CPUs ...\n");
611 
612     /* FIXME: This should be done in userspace --RR */
613     for_each_present_cpu(cpu) {
614         if (num_online_cpus() >= setup_max_cpus)
615             break;
616         pr_info("====cpuhp-walk:before bringing up cpu:%d\n", cpu);
617         if (!cpu_online(cpu))
618             cpu_up(cpu);
619         pr_info("====cpuhp-walk:after bringing up cpu:%d\n", cpu);
620     }
621 
622     num_nodes = num_online_nodes();
623     num_cpus  = num_online_cpus();
624     pr_info("====cpuhp-walk:Brought up %d node%s, %d CPU%s\n",
625         num_nodes, (num_nodes > 1 ? "s" : ""),
626         num_cpus,  (num_cpus  > 1 ? "s" : ""));
627 
628     /* Any cleanup work */
629     smp_cpus_done(setup_max_cpus);
630 }

可以看得出在smp_init中，cpu0依次调用cpu_up启动其他的cpu，启动完成一个，再启动下一个，直到所有cpu都启动完毕，才继续内核剩余的启动流程，整个过程从smp_init开始，从smp_init结束。

下面分析具体的过程，我们将启动其他cpu成为BP(boot cpu)，将被启动的cpu成为AP(不知道A表示哪个单词)：

BP                                                                                                        AP
smp_init                                                                                                         |    do_cpu_up|        --> cpuhp_invoke_callback|            --> smpboot_create_threads|                perf_event_init_cpu|                workqueue_prepare_cpu|                hrtimers_prepare_cpu|                ...|                bringup_cpu|                    -->__cpu_up|                        -->boot_secondary (cpu_ops[cpu]->cpu_boot(cpu))|                            --> cpu_psci_cpu_boot|                                -->psci_cpu_on (invoke_psci_fn(0xc4000003, cpuid, secondary_entry, 0);)|                                                                                                            secondary_entrynext cpu                                                                                                        --> secondary_startup|                                                                                                                    --> __secondary_switched|                                                                                                                        -->secondary_start_kernel          |                                                                                                                            --> notify_cpu_starting|                                                                                                                                -->cpuhp_invoke_callback|                                                                                                                                    -->sched_cpu_starting|                                                                                                                                        gic_starting_cpu|                                                                                                                                        arch_timer_starting_cpu|                                                                                                                                        dummy_timer_starting_cpu|            |            bringup_wait_for_ap

可以看出，BP通过bringup_cpu函数，调用psci的函数，请求firmware启动AP，然后原地等待AP启动的结果。

firmware给AP上电之后，AP进入head.S中的secondary_entry，然后进入secondary_start_kernel，完成一系列回调之后，通知BP自己启动成功。BP从bringup_wait_for_ap返回，继续启动下一个cpu。

在cpuhp_invoke_callback所调用的回调函数的定义在这：

kernel/cpu.c1426 /* Boot processor state steps */
1427 static struct cpuhp_step cpuhp_hp_states[] = {
1428     [CPUHP_OFFLINE] = {
1429         .name           = "offline",
1430         .startup.single     = NULL,
1431         .teardown.single    = NULL,
1432     },
1433 #ifdef CONFIG_SMP
1434     [CPUHP_CREATE_THREADS]= {
1435         .name           = "threads:prepare",
1436         .startup.single     = smpboot_create_threads,
1437         .teardown.single    = NULL,
1438         .cant_stop      = true,
1439     },
1440     [CPUHP_PERF_PREPARE] = {
1441         .name           = "perf:prepare",
1442         .startup.single     = perf_event_init_cpu,
1443         .teardown.single    = perf_event_exit_cpu,
1444     },
1445     [CPUHP_WORKQUEUE_PREP] = {
1446         .name           = "workqueue:prepare",
1447         .startup.single     = workqueue_prepare_cpu,
1448         .teardown.single    = NULL,
1449     },
1450     [CPUHP_HRTIMERS_PREPARE] = {
1451         .name           = "hrtimers:prepare",
1452         .startup.single     = hrtimers_prepare_cpu,
1453         .teardown.single    = hrtimers_dead_cpu,
1454     },
1455     [CPUHP_SMPCFD_PREPARE] = {
1456         .name           = "smpcfd:prepare",
1457         .startup.single     = smpcfd_prepare_cpu,
1458         .teardown.single    = smpcfd_dead_cpu,
1459     },
1460     [CPUHP_RELAY_PREPARE] = {
1461         .name           = "relay:prepare",
1462         .startup.single     = relay_prepare_cpu,
1463         .teardown.single    = NULL,
1464     },
1465     [CPUHP_SLAB_PREPARE] = {
1466         .name           = "slab:prepare",
1467         .startup.single     = slab_prepare_cpu,
1468         .teardown.single    = slab_dead_cpu,
1469     },
1470     [CPUHP_RCUTREE_PREP] = {
1471         .name           = "RCU/tree:prepare",
...
1485     /* Kicks the plugged cpu into life */
1486     [CPUHP_BRINGUP_CPU] = {
1487         .name           = "cpu:bringup",
1488         .startup.single     = bringup_cpu,
1489         .teardown.single    = NULL,
1490         .cant_stop      = true,
1491     },
1492     /* Final state before CPU kills itself */
1493     [CPUHP_AP_IDLE_DEAD] = {
1494         .name           = "idle:dead",
1495     },
1496     /*
1497      * Last state before CPU enters the idle loop to die. Transient state
1498      * for synchronization.
1499      */
1500     [CPUHP_AP_OFFLINE] = {
1501         .name           = "ap:offline",
1502         .cant_stop      = true,
1503     },
1504     /* First state is scheduler control. Interrupts are disabled */
1505     [CPUHP_AP_SCHED_STARTING] = {
1506         .name           = "sched:starting",
1507         .startup.single     = sched_cpu_starting,
1508         .teardown.single    = sched_cpu_dying,
1509     },
1510     [CPUHP_AP_RCUTREE_DYING] = {
1511         .name           = "RCU/tree:dying",
1512         .startup.single     = NULL,
1513         .teardown.single    = rcutree_dying_cpu,
1514     },
1515     [CPUHP_AP_SMPCFD_DYING] = {
1516         .name           = "smpcfd:dying",
1517         .startup.single     = NULL,
1518         .teardown.single    = smpcfd_dying_cpu,
1519     },
1520     /* Entry state on starting. Interrupts enabled from here on. Transient
1521      * state for synchronsization */
1522     [CPUHP_AP_ONLINE] = {
1523         .name           = "ap:online",
1524     },
1525     /*
1526      * Handled on controll processor until the plugged processor manages
1527      * this itself.
1528      */
1529     [CPUHP_TEARDOWN_CPU] = {
1530         .name           = "cpu:teardown",
1531         .startup.single     = NULL,
...
1535     /* Handle smpboot threads park/unpark */
1536     [CPUHP_AP_SMPBOOT_THREADS] = {
1537         .name           = "smpboot/threads:online",
1538         .startup.single     = smpboot_unpark_threads,
1539         .teardown.single    = smpboot_park_threads,
1540     },
1541     [CPUHP_AP_IRQ_AFFINITY_ONLINE] = {
1542         .name           = "irq/affinity:online",
1543         .startup.single     = irq_affinity_online_cpu,
1544         .teardown.single    = NULL,
1545     },
1546     [CPUHP_AP_PERF_ONLINE] = {
1547         .name           = "perf:online",
1548         .startup.single     = perf_event_init_cpu,
1549         .teardown.single    = perf_event_exit_cpu,
1550     },
1551     [CPUHP_AP_WATCHDOG_ONLINE] = {
1552         .name           = "lockup_detector:online",
1553         .startup.single     = lockup_detector_online_cpu,
1554         .teardown.single    = lockup_detector_offline_cpu,
1555     },
1556     [CPUHP_AP_WORKQUEUE_ONLINE] = {
1557         .name           = "workqueue:online",
1558         .startup.single     = workqueue_online_cpu,
1559         .teardown.single    = workqueue_offline_cpu,
1560     },
1561     [CPUHP_AP_RCUTREE_ONLINE] = {
1562         .name           = "RCU/tree:online",
1563         .startup.single     = rcutree_online_cpu,
1564         .teardown.single    = rcutree_offline_cpu,
1565     },
1566 #endif
1567     /*
1568      * The dynamically registered state space is here
1569      */
1570 
1571 #ifdef CONFIG_SMP
1572     /* Last state is scheduler control setting the cpu active */
1573     [CPUHP_AP_ACTIVE] = {
1574         .name           = "sched:active",
1575         .startup.single     = sched_cpu_activate,
1576         .teardown.single    = sched_cpu_deactivate,
1577     },
1578 #endif
1579 
1580     /* CPU is fully up and running. */
1581     [CPUHP_ONLINE] = {
1582         .name           = "online",
1583         .startup.single     = NULL,
1584         .teardown.single    = NULL,
1585     },
1586 };1482,3-9      60

所有的回调函数一次调用，最重要的是bringup_cpu，这个是通过firmware直接给cpu上电启动的过程。

psci通过设备树节点获取与固件通信的方法（method：smc）,smc具体的操作指令，可以在include/uapi/linux/psci.h中查找.

我在代码中增加一些打印语句，完整的smp_init的过程如下：

[    0.064050] smp: ====cpuhp-walk:Bringing up secondary CPUs ...
[    0.064051] smp: ====cpuhp-walk:before bringing up cpu:0
[    0.064052] smp: ====cpuhp-walk:after bringing up cpu:0
[    0.064053] smp: ====cpuhp-walk:before bringing up cpu:1
[    0.064053] cpuhp_walk:cpu:1,do_cpu_up
[    0.064060] cphp_walk:cpu:1,cpuhp_up_callbacks
[    0.064061] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:smpboot_create_threads+0x0/0xe0
[    0.104074] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:perf_event_init_cpu+0x0/0x140
[    0.104080] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:workqueue_prepare_cpu+0x0/0x98
[    0.112080] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:hrtimers_prepare_cpu+0x0/0xb0
[    0.112084] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:smpcfd_prepare_cpu+0x0/0x70
[    0.112089] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:relay_prepare_cpu+0x0/0xf8
[    0.112092] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:rcutree_prepare_cpu+0x0/0x1c0
[    0.112099] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:timers_prepare_cpu+0x0/0x80
[    0.112101] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:bringup_cpu+0x0/0x140
[    0.112104] cpuhp_walk:cpu:1,bringup_cpu
[    0.112105] cpuhp_walk:cpu:1,__cpu_up
[    0.112106] cpuhp_walk:cpu:1,boot_secondary, cpu_boot:cpu_psci_cpu_boot+0x0/0x94
[    0.112109] psci: cpuhp_walk:cpu:1,cpu_psci_cpu_boot, cpu_on:psci_cpu_on+0x0/0x94
[    0.112112] psci: cphp_walk:cpuid:1,psci_cpu_on, fn:0xc4000003
[    0.145924] cphp_walk:cpu:1,secondary_start_kernel
[    0.145934] Detected PIPT I-cache on CPU1
[    0.145942] cpuhp_walk:cpu:1,notify_cpu_starting
[    0.145943] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:sched_cpu_starting+0x0/0x120
[    0.145946] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:gic_starting_cpu+0x0/0x40
[    0.145950] GICv3: CPU1: found redistributor 1 region 1:0x00000000299a0000
[    0.145958] GICv3: CPU1: using allocated LPI pending table @0x0000002176620000
[    0.145964] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:arch_timer_starting_cpu+0x0/0x318
[    0.145971] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:dummy_timer_starting_cpu+0x0/0x88
[    0.145973] cpuhp_walk, CPU1: Booted secondary processor 0x0000000001 [0x701f6633]
[    0.145978] cpuhp_walk:cpu:1,bringup_cpu, wait ap
[    0.145980] cphp_walk:cpu:1,bringup_wait_for_ap, 1
[    0.145984] cphp_walk:cpu:1,bringup_wait_for_ap, 2
[    0.145987] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:smpboot_unpark_threads+0x0/0xb0
[    0.145994] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:irq_affinity_online_cpu+0x0/0x110
[    0.145998] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:perf_event_init_cpu+0x0/0x140
[    0.146002] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:workqueue_online_cpu+0x0/0x228
[    0.146019] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:rcutree_online_cpu+0x0/0x98
[    0.146022] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:page_writeback_cpu_online+0x0/0x20
[    0.146025] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:vmstat_cpu_online+0x0/0x70
[    0.146029] cphp_walk:cpu:1,cpuhp_invoke_callback, 1.1, cb:sched_cpu_activate+0x0/0x168
[    0.146035] smp: ====cpuhp-walk:after bringing up cpu:1
[    0.146036] smp: ====cpuhp-walk:before bringing up cpu:2
[    0.146037] cpuhp_walk:cpu:2,do_cpu_up
[    0.146041] cphp_walk:cpu:2,cpuhp_up_callbacks
[    0.146042] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:smpboot_create_threads+0x0/0xe0
[    0.185939] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:perf_event_init_cpu+0x0/0x140
[    0.185943] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:workqueue_prepare_cpu+0x0/0x98
[    0.193946] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:hrtimers_prepare_cpu+0x0/0xb0
[    0.193949] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:smpcfd_prepare_cpu+0x0/0x70
[    0.193952] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:relay_prepare_cpu+0x0/0xf8
[    0.193954] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:rcutree_prepare_cpu+0x0/0x1c0
[    0.193959] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:timers_prepare_cpu+0x0/0x80
[    0.193961] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:bringup_cpu+0x0/0x140
[    0.193964] cpuhp_walk:cpu:2,bringup_cpu
[    0.193964] cpuhp_walk:cpu:2,__cpu_up
[    0.193965] cpuhp_walk:cpu:2,boot_secondary, cpu_boot:cpu_psci_cpu_boot+0x0/0x94
[    0.193967] psci: cpuhp_walk:cpu:2,cpu_psci_cpu_boot, cpu_on:psci_cpu_on+0x0/0x94
[    0.193969] psci: cphp_walk:cpuid:256,psci_cpu_on, fn:0xc4000003
[    0.227952] cphp_walk:cpu:2,secondary_start_kernel
[    0.227961] Detected PIPT I-cache on CPU2
[    0.227967] cpuhp_walk:cpu:2,notify_cpu_starting
[    0.227968] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:sched_cpu_starting+0x0/0x120
[    0.227972] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:gic_starting_cpu+0x0/0x40
[    0.227976] GICv3: CPU2: found redistributor 100 region 2:0x00000000299c0000
[    0.227994] GICv3: CPU2: using allocated LPI pending table @0x0000002176630000
[    0.227999] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:arch_timer_starting_cpu+0x0/0x318
[    0.228007] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:dummy_timer_starting_cpu+0x0/0x88
[    0.228010] cpuhp_walk, CPU2: Booted secondary processor 0x0000000100 [0x701f6633]
[    0.228017] cpuhp_walk:cpu:2,bringup_cpu, wait ap
[    0.228019] cphp_walk:cpu:2,bringup_wait_for_ap, 1
[    0.228022] cphp_walk:cpu:2,bringup_wait_for_ap, 2
[    0.228029] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:smpboot_unpark_threads+0x0/0xb0
[    0.228039] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:irq_affinity_online_cpu+0x0/0x110
[    0.228042] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:perf_event_init_cpu+0x0/0x140
[    0.228047] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:workqueue_online_cpu+0x0/0x228
[    0.228070] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:rcutree_online_cpu+0x0/0x98
[    0.228073] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:page_writeback_cpu_online+0x0/0x20
[    0.228076] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:vmstat_cpu_online+0x0/0x70
[    0.228080] cphp_walk:cpu:2,cpuhp_invoke_callback, 1.1, cb:sched_cpu_activate+0x0/0x168
[    0.228086] smp: ====cpuhp-walk:after bringing up cpu:2
[    0.228087] smp: ====cpuhp-walk:before bringing up cpu:3
[    0.228088] cpuhp_walk:cpu:3,do_cpu_up
[    0.228092] cphp_walk:cpu:3,cpuhp_up_callbacks
[    0.228093] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:smpboot_create_threads+0x0/0xe0
[    0.267968] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:perf_event_init_cpu+0x0/0x140
[    0.267972] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:workqueue_prepare_cpu+0x0/0x98
[    0.275974] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:hrtimers_prepare_cpu+0x0/0xb0
[    0.275977] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:smpcfd_prepare_cpu+0x0/0x70
[    0.275980] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:relay_prepare_cpu+0x0/0xf8
[    0.275983] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:rcutree_prepare_cpu+0x0/0x1c0
[    0.275988] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:timers_prepare_cpu+0x0/0x80
[    0.275990] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:bringup_cpu+0x0/0x140
[    0.275993] cpuhp_walk:cpu:3,bringup_cpu
[    0.275994] cpuhp_walk:cpu:3,__cpu_up
[    0.275995] cpuhp_walk:cpu:3,boot_secondary, cpu_boot:cpu_psci_cpu_boot+0x0/0x94
[    0.275996] psci: cpuhp_walk:cpu:3,cpu_psci_cpu_boot, cpu_on:psci_cpu_on+0x0/0x94
[    0.275998] psci: cphp_walk:cpuid:257,psci_cpu_on, fn:0xc4000003
[    0.309980] cphp_walk:cpu:3,secondary_start_kernel
[    0.309985] Detected PIPT I-cache on CPU3
[    0.309989] cpuhp_walk:cpu:3,notify_cpu_starting
[    0.309990] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:sched_cpu_starting+0x0/0x120
[    0.309993] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:gic_starting_cpu+0x0/0x40
[    0.309996] GICv3: CPU3: found redistributor 101 region 3:0x00000000299e0000
[    0.310002] GICv3: CPU3: using allocated LPI pending table @0x0000002176640000
[    0.310007] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:arch_timer_starting_cpu+0x0/0x318
[    0.310012] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:dummy_timer_starting_cpu+0x0/0x88
[    0.310014] cpuhp_walk, CPU3: Booted secondary processor 0x0000000101 [0x701f6633]
[    0.310019] cpuhp_walk:cpu:3,bringup_cpu, wait ap
[    0.310021] cphp_walk:cpu:3,bringup_wait_for_ap, 1
[    0.310024] cphp_walk:cpu:3,bringup_wait_for_ap, 2
[    0.310028] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:smpboot_unpark_threads+0x0/0xb0
[    0.310036] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:irq_affinity_online_cpu+0x0/0x110
[    0.310039] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:perf_event_init_cpu+0x0/0x140
[    0.310043] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:workqueue_online_cpu+0x0/0x228
[    0.310050] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:rcutree_online_cpu+0x0/0x98
[    0.310052] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:page_writeback_cpu_online+0x0/0x20
[    0.310054] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:vmstat_cpu_online+0x0/0x70
[    0.310057] cphp_walk:cpu:3,cpuhp_invoke_callback, 1.1, cb:sched_cpu_activate+0x0/0x168
[    0.310063] smp: ====cpuhp-walk:after bringing up cpu:3
[    0.310064] smp: ====cpuhp-walk:Brought up 1 node, 4 CPUs
[    0.310066] SMP: Total of 4 processors activated.
[    0.310067] CPU features: detected: 32-bit EL0 Support
[    0.310069] CPU features: detected: CRC32 instructions
[    0.310303] CPU: All CPU(s) started at EL2

经查，是CPU厂商firmware的问题， 也就是psci_cpu_on, fn:0xc4000003的问题。

所以以后遇到这样的问题，熟悉了过程，就不慌了。

本文的psci部分由我的同事提供，同时，在阅读和分析代码之前，我还参照了如下链接的信息：

https://www.cnblogs.com/pengdonglin137/p/11925299.html

https://zhuanlan.zhihu.com/p/538782115

https://blog.csdn.net/weixin_45264425/article/details/127895018

https://zhuanlan.zhihu.com/p/545550388

此外，由于功耗控制的原因，系统运行期间，还会通过cpu idle来间断的关闭和打开cpu，也就是cpu hotplug，打开cpu的操作和上述过程相同，关闭cpu的过程与cpu up相反，读者自行阅读代码，也是通过psci来关闭cpu。