浅析linux内核中timer定时器的生成和sofirq软中断调用流程【转】-阿里云开发者社区

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_softirq, NULL); 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; }