浅析linux内核中timer定时器的生成和sofirq软中断调用流程【转】

转自:http://blog.chinaunix.net/uid-20564848-id-73480.html

浅析linux内核中timer定时器的生成和sofirq软中断调用流程

  mod_timer添加的定时器timer在内核的软中断中发生调用,__run_timers会spin_lock_irq(&base->lock);禁止cpu中断,所以我们的timer回调处理函数handler工作在irq关闭的环境中,所以需要作很多考虑,比如在handler中尽量不要执行会引起pending的函数调用,比如kmalloc之类可能引起pending的操作,否则会使kernel永远停在我们的handler中不能返回,这样kernel将因为我们ko设计上的失败而死机[luther.gliethttp]!
  我们可以使用如下几行语句,向我们的ko驱动添加一个timer定时器,来处理时间事件:
struct __wlanwlan_check_tx_flow_timer
{
    struct timer_list timer;
    int timer_freq;
} wlan_check_tx_flow_timer {
        .timer_freq = 8*1000,
};
static void wlan_check_tx_flow_timer_handler(unsigned long data)
{
    ...
    //重新启动timer定时器 
    mod_timer(&wlan_check_tx_flow_timer.timer, jiffies + msecs_to_jiffies(wlan_check_tx_flow_timer.timer_freq));
    ...
}
//设置定时器
setup_timer(&wlan_check_tx_flow_timer.timer, wlan_check_tx_flow_timer_handler(unsigned long)&wlan_check_tx_flow_timer);
//添加定时器
mod_timer(&wlan_check_tx_flow_timer.timer, jiffies + msecs_to_jiffies(wlan_check_tx_flow_timer.timer_freq));

那么这个wlan_check_tx_flow_timer_handler处理函数在什么时候被调用的呢?那么我们追入内核中,看看kernel对定时器的具体管理.
首先kernel在启动的最前面注册TIMER_SOFTIRQ的处理函数[luther.gliethttp],
start_kernel
=>init_timers
=>open_softirq(TIMER_SOFTIRQ, run_timer_softirqNULL);
那么由谁来调用raise_softirq(TIMER_SOFTIRQ);触发TIMER_SOFTIRQ软中断呢,这就和平台相关了,对于pxa935处理器来说[luther.gliethttp],
MACHINE_START(LUTHER"luther")
    .phys_io = 0x40000000,
    .boot_params = 0xa0000100,
    .io_pg_offst (io_p2v(0x40000000>> 18& 0xfffc,
    .map_io = pxa_map_io,
    .init_irq = pxa3xx_init_irq,
    .timer &pxa_timer,
    .init_machine = luther_init,
MACHINE_END
=>pxa_timer_init//平台对应的定时器初始化
==>pxa_timer_irq.dev_id &ckevt_32ktimer;
==>setup_irq(IRQ_OST_4_11&pxa_timer_irq)//32768的rtc
==>clockevents_register_device(&ckevt_32ktimer);

pxa_timer_interrupt中断处理函数
=>c->event_handler(c);也就是tick_handle_periodic系统时钟函数
=>tick_handle_periodic
=>update_process_times
=>run_local_timers
=>raise_softirq(TIMER_SOFTIRQ);
这里仅仅是触发了TIMER_SOFTIRQ软中断,那么在什么地方处理我们mod_timer添加的timer定时器处理函数wlan_check_tx_flow_timer_handler呢[luther.gliethttp]?
__irq_svc://内核中发生的中断
__irq_usr://用户空间时发生的中断
=>asm_do_IRQ
=>irq_exit =>do_softirq =>__do_softirq =>调用上面注册的run_timer_softirq软中断处理函数 =>run_timer_softirq =>__run_timers static inline void __run_timers(struct tvec_base *base) {     struct timer_list *timer;     spin_lock_irq(&base->lock);//禁止中断     while (time_after_eq(jiffies, base->timer_jiffies)) {         ...         if (时间到了) {         ...         fn = timer->function;         data = timer->data;         fn(data);//这就是我们上面添加的static void wlan_check_tx_flow_timer_handler(unsigned long data);定时器处理函数了.         ...         }         ...     }     set_running_timer(base, NULL);     spin_unlock_irq(&base->lock);//打开中断 } //================ include/asm/hardirq.h typedef struct {     unsigned int __softirq_pending;     unsigned int local_timer_irqs; } ____cacheline_aligned irq_cpustat_t; //================ kernel/softirq.c|45| irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned; #ifndef __ARCH_IRQ_STAT irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;//在这里定义irq_stat存储空间 EXPORT_SYMBOL(irq_stat); #endif //================ include/linux/irq_cpustat.h #ifndef __ARCH_IRQ_STAT //引用的就是上面的irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned; extern irq_cpustat_t irq_stat[];        /* defined in asm/hardirq.h */ #define __IRQ_STAT(cpu, member)    (irq_stat[cpu].member) #endif //================ arch/arm/kernel/entry-armv.S|331| .word    irq_stat #ifdef CONFIG_PREEMPT svc_preempt:     teq    r8, #0                @ was preempt count = 0     ldreq    r6, .LCirq_stat //操作     movne    pc, lr                @ no     ldr    r0, [r6, #4]            @ local_irq_count     ldr    r1, [r6, #8]            @ local_bh_count     adds    r0, r0, r1     movne    pc, lr     mov    r7, #0                @ preempt_schedule_irq     str    r7, [tsk, #TI_PREEMPT]        @ expects preempt_count == 0 1:    bl    preempt_schedule_irq        @ irq en/disable is done inside     ldr    r0, [tsk, #TI_FLAGS]        @ get new tasks TI_FLAGS     tst    r0, #_TIF_NEED_RESCHED     beq    preempt_return            @ go again     b    1b #endif .LCirq_stat:     .word    irq_stat //引用irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;地址 #endif   /* arch independent irq_stat fields */ #define local_softirq_pending() \     __IRQ_STAT(smp_processor_id(), __softirq_pending) #define __ARCH_IRQ_EXIT_IRQS_DISABLED    1 #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED # define invoke_softirq()    __do_softirq() //是这个 #else # define invoke_softirq()    do_softirq() #endif #ifndef __ARCH_SET_SOFTIRQ_PENDING #define set_softirq_pending(x) (local_softirq_pending() = (x)) #define or_softirq_pending(x) (local_softirq_pending() |= (x)) #endif #define __raise_softirq_irqoff(nr) do { or_softirq_pending(1UL << (nr)); } while (0) inline void raise_softirq_irqoff(unsigned int nr) {     __raise_softirq_irqoff(nr);         if (!in_interrupt())         wakeup_softirqd(); } void raise_softirq(unsigned int nr) {     unsigned long flags;     local_irq_save(flags);     raise_softirq_irqoff(nr);     local_irq_restore(flags); } =>s3c2410_timer_interrupt =>timer_tick =>pxa_timer_init ==>pxa_timer_irq.dev_id = &ckevt_32ktimer; ==>setup_irq(IRQ_OST_4_11, &pxa_timer_irq); //32768的rtc ==>clockevents_register_device(&ckevt_32ktimer); =>clockevents_register_device =>clockevents_do_notify =>raw_notifier_call_chain(&clockevents_chain, reason, dev); =>__raw_notifier_call_chain =>notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); =>nb->notifier_call(nb, val, v);就是tick_notify start_kernel =>tick_init static struct notifier_block tick_notifier = {     .notifier_call = tick_notify, }; void __init tick_init(void) {     clockevents_register_notifier(&tick_notifier); } clockevents_register_notifier =>raw_notifier_chain_register(&clockevents_chain, nb); =>notifier_chain_register将tick_notifier添加到clockevents_chain这个单向链表中[luther.gliethttp] static int tick_notify(struct notifier_block *nb, unsigned long reason,              void *dev) {     switch (reason) {     case CLOCK_EVT_NOTIFY_ADD:         return tick_check_new_device(dev);     ...     return NOTIFY_OK; } =>tick_notify =>tick_check_new_device =>tick_setup_device(td, newdev, cpu, cpumask); static void tick_setup_device(struct tick_device *td,              struct clock_event_device *newdev, int cpu,              cpumask_t cpumask) {     ktime_t next_event;     void (*handler)(struct clock_event_device *) = NULL;     /*      * First device setup ?      */     if (!td->evtdev) {         /*          * If no cpu took the do_timer update, assign it to          * this cpu:          */         if (tick_do_timer_cpu == -1) {             tick_do_timer_cpu = cpu;             tick_next_period = ktime_get();             tick_period = ktime_set(0, NSEC_PER_SEC / HZ);         }         /*          * Startup in periodic mode first.          */         td->mode = TICKDEV_MODE_PERIODIC;//设置第1个tick设备为TICKDEV_MODE_PERIODIC模式     } else {         handler = td->evtdev->event_handler;         next_event = td->evtdev->next_event;     }     td->evtdev = newdev;     ...     if (td->mode == TICKDEV_MODE_PERIODIC)         tick_setup_periodic(newdev, 0);     else         tick_setup_oneshot(newdev, handler, next_event); } void tick_setup_periodic(struct clock_event_device *dev, int broadcast) {     tick_set_periodic_handler(dev, broadcast);//设置event_handler处理函数为dev->event_handler = tick_handle_periodic;     /* Broadcast setup ? */     if (!tick_device_is_functional(dev))         return;     if (dev->features & CLOCK_EVT_FEAT_PERIODIC) {         clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);     } else {         unsigned long seq;         ktime_t next;         do {             seq = read_seqbegin(&xtime_lock);             next = tick_next_period;         } while (read_seqretry(&xtime_lock, seq));         clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);         for (;;) {             if (!clockevents_program_event(dev, next, ktime_get()))                 return;             next = ktime_add(next, tick_period);         }     } } void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast) {     if (!broadcast)         dev->event_handler = tick_handle_periodic;     else         dev->event_handler = tick_handle_periodic_broadcast; } =>pxa_timer_interrupt {     ...     if (OSSR & OST_C4) {         OIER &= ~OST_C4;         OSSR = OST_C4;         if (timer32k_enabled)             c->event_handler(c);//调用tick_handle_periodic处理函数,作为     }     ... } void tick_handle_periodic(struct clock_event_device *dev) {     int cpu = smp_processor_id();     ktime_t next;     tick_periodic(cpu);//调用do_timer(1);将jiffies_64加1     if (dev->mode != CLOCK_EVT_MODE_ONESHOT)         return;     /*      * Setup the next period for devices, which do not have      * periodic mode:      */     next = ktime_add(dev->next_event, tick_period);     for (;;) {         if (!clockevents_program_event(dev, next, ktime_get()))             return;         tick_periodic(cpu);         next = ktime_add(next, tick_period);     } } static void tick_periodic(int cpu) {     if (tick_do_timer_cpu == cpu) {         write_seqlock(&xtime_lock);         /* Keep track of the next tick event */         tick_next_period = ktime_add(tick_next_period, tick_period);         do_timer(1);         write_sequnlock(&xtime_lock);     }     update_process_times(user_mode(get_irq_regs()));     profile_tick(CPU_PROFILING); } arch/arm/kernel/time.c|332| update_process_times(user_mode(get_irq_regs())); =>update_process_times =>run_local_timers =>raise_softirq(TIMER_SOFTIRQ);//触发软中断,当irq_exit时调用__do_softirq来处理 =>run_timer_softirq =>__run_timers => fn = timer->function;//执行 data = timer->data; fn(data); //================ include/asm/arch-pxa/entry-macro.S|22| .macro    get_irqnr_and_base, irqnr, irqstat, base, tmp //pxa获取irq中断号函数 //================ arch/arm/kernel/entry-armv.S|37| bne    asm_do_IRQ     .macro    irq_handler     get_irqnr_preamble r5, lr 1:    get_irqnr_and_base r0, r6, r5, lr //获取irq中断号,存储到r0寄存器中,作为参数传递给asm_do_IRQ     movne    r1, sp     @     @ routine called with r0 = irq number, r1 = struct pt_regs *     @     adrne    lr, 1b     bne    asm_do_IRQ     ... //================     .align    5 __irq_svc://内核中发生的中断     svc_entry     ...     irq_handler     ... //================     .align    5 __irq_usr://用户空间时发生的中断     usr_entry     ...     irq_handler     ... //================     .macro    vector_stub, name, mode, correction=0     .align    5 vector_\name:     .if \correction     sub    lr, lr, #\correction     .endif     @     @ Save r0, lr_<exception> (parent PC) and spsr_<exception>     @ (parent CPSR)     @     stmia    sp, {r0, lr}        @ save r0, lr     mrs    lr, spsr     str    lr, [sp, #8]        @ save spsr     @     @ Prepare for SVC32 mode. IRQs remain disabled.     @     mrs    r0, cpsr     eor    r0, r0, #(\mode ^ SVC_MODE)     msr    spsr_cxsf, r0     @     @ the branch table must immediately follow this code     @     and    lr, lr, #0x0f //lr存储了spsr,所以一共有16种cpu模式     mov    r0, sp //传参     ldr    lr, [pc, lr, lsl #2]//取出相应模式下的处理函数指针,比如__irq_usr或者__irq_svc     movs    pc, lr            @ branch to handler in SVC mode     .endm //================     .globl    __stubs_start __stubs_start: /*  * Interrupt dispatcher  */     vector_stub    irq, IRQ_MODE, 4     .long    __irq_usr            @ 0 (USR_26 / USR_32)     .long    __irq_invalid        @ 1 (FIQ_26 / FIQ_32)     .long    __irq_invalid        @ 2 (IRQ_26 / IRQ_32)     .long    __irq_svc            @ 3 (SVC_26 / SVC_32)     .long    __irq_invalid            @ 4     .long    __irq_invalid            @ 5     .long    __irq_invalid            @ 6     .long    __irq_invalid            @ 7     .long    __irq_invalid            @ 8     .long    __irq_invalid            @ 9     .long    __irq_invalid            @ a     .long    __irq_invalid            @ b     .long    __irq_invalid            @ c     .long    __irq_invalid            @ d     .long    __irq_invalid            @ e     .long    __irq_invalid            @ f //================     .globl    __vectors_start __vectors_start:     swi    SYS_ERROR0     b    vector_und + stubs_offset     ldr    pc, .LCvswi + stubs_offset     b    vector_pabt + stubs_offset     b    vector_dabt + stubs_offset     b    vector_addrexcptn + stubs_offset     b    vector_irq + stubs_offset     b    vector_fiq + stubs_offset //================ asm_do_IRQ(unsigned int irq, struct pt_regs *regs) =>desc_handle_irq(irq, desc);// static inline void desc_handle_irq(unsigned int irq, struct irq_desc *desc) {     desc->handle_irq(irq, desc);//调用中断号irq对应的handler回调处理函数[luther.gliethttp] } __irq_svc://内核中发生的中断 __irq_usr://用户空间时发生的中断 =>asm_do_IRQ =>irq_exit =>do_softirq =>__do_softirq => {     ...     h = softirq_vec;//执行软中断函数     do {         if (pending & 1) {             h->action(h); //如果32768的时间到达,那asm_do_IRQ中将触发raise_softirq(TIMER_SOFTIRQ); //在这里将执行管理系统tick的run_timer_softirq软中断[luther.gliethttp]             rcu_bh_qsctr_inc(cpu);         }         h++;         pending >>= 1;     } while (pending);     ... } start_kernel =>init_timers =>open_softirq(TIMER_SOFTIRQ, run_timer_softirq, NULL); void open_softirq(int nr, void (*action)(struct softirq_action*), void *data) {     softirq_vec[nr].data = data;     softirq_vec[nr].action = action; } static void run_timer_softirq(struct softirq_action *h) {     struct tvec_base *base = __get_cpu_var(tvec_bases);//获得time时间根     hrtimer_run_pending();     if (time_after_eq(jiffies, base->timer_jiffies))         __run_timers(base); } //执行软中断 =>run_timer_softirq =>__run_timers => fn = timer->function; data = timer->data; fn(data); static inline void __run_timers(struct tvec_base *base) {     ...     spin_lock_irq(&base->lock);//禁止中断     ...     fn = timer->function;     data = timer->data;     fn(data);     ...     set_running_timer(base, NULL);     spin_unlock_irq(&base->lock);//打开中断 } mod_timer =>__mod_timer int __mod_timer(struct timer_list *timer, unsigned long expires) {     struct tvec_base *base, *new_base;     unsigned long flags;     int ret = 0;     timer_stats_timer_set_start_info(timer);     BUG_ON(!timer->function);     base = lock_timer_base(timer, &flags);     if (timer_pending(timer)) {         detach_timer(timer, 0);         ret = 1;     }     new_base = __get_cpu_var(tvec_bases);//获得time时间根     if (base != new_base) {         /*          * We are trying to schedule the timer on the local CPU.          * However we can't change timer's base while it is running,          * otherwise del_timer_sync() can't detect that the timer's          * handler yet has not finished. This also guarantees that          * the timer is serialized wrt itself.          */         if (likely(base->running_timer != timer)) {             /* See the comment in lock_timer_base() */             timer_set_base(timer, NULL);             spin_unlock(&base->lock);             base = new_base;             spin_lock(&base->lock);             timer_set_base(timer, base);         }     }     timer->expires = expires;     internal_add_timer(base, timer); //添加到链表上,这样当timer超时到达时,run_timer_softirq=>__run_timers软中断中将会回调该处理函数[luther.gliethttp].     spin_unlock_irqrestore(&base->lock, flags);     return ret; }















本文转自张昺华-sky博客园博客,原文链接:http://www.cnblogs.com/sky-heaven/p/7246640.html,如需转载请自行联系原作者


上一篇:利用ssh-copy-id实现SSH无密码登录


下一篇:钉钉群直播【基于Spark实现的MLSQL如何帮助企业构建数据中台】