张备《Linux内核分析》MOOC课程http://mooc.study.163.com/course/USTC-1000029000
1.进程切换函数
schedule函数为调度函数,用以选择切换进程,其主要调用的函数有 pick_next_task,context_switch,在context_switch中调用switch_to (1)schedule
static void __sched __schedule(void) { struct task_struct *prev, *next; unsigned long *switch_count; struct rq *rq; int cpu; need_resched: preempt_disable(); cpu = smp_processor_id(); rq = cpu_rq(cpu); rcu_note_context_switch(cpu); prev = rq->curr; schedule_debug(prev); if (sched_feat(HRTICK)) hrtick_clear(rq); smp_mb__before_spinlock(); raw_spin_lock_irq(&rq->lock); switch_count = &prev->nivcsw; if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) { if (unlikely(signal_pending_state(prev->state, prev))) { prev->state = TASK_RUNNING; } else { deactivate_task(rq, prev, DEQUEUE_SLEEP); prev->on_rq = 0; if (prev->flags & PF_WQ_WORKER) { struct task_struct *to_wakeup; to_wakeup = wq_worker_sleeping(prev, cpu); if (to_wakeup) try_to_wake_up_local(to_wakeup); } } switch_count = &prev->nvcsw; } if (task_on_rq_queued(prev) || rq->skip_clock_update < 0) update_rq_clock(rq); next = pick_next_task(rq, prev); clear_tsk_need_resched(prev); clear_preempt_need_resched(); rq->skip_clock_update = 0; if (likely(prev != next)) { rq->nr_switches++; rq->curr = next; ++*switch_count; context_switch(rq, prev, next); /* unlocks the rq */ cpu = smp_processor_id(); rq = cpu_rq(cpu); } else raw_spin_unlock_irq(&rq->lock); post_schedule(rq); sched_preempt_enable_no_resched(); if (need_resched()) goto need_resched; }(2) pick_next_task //进程调度算法都封装这个函数内部
static inline struct task_struct * pick_next_task(struct rq *rq, struct task_struct *prev) { const struct sched_class *class = &fair_sched_class; struct task_struct *p; if (likely(prev->sched_class == class && rq->nr_running == rq->cfs.h_nr_running)) { p = fair_sched_class.pick_next_task(rq, prev); if (unlikely(p == RETRY_TASK)) goto again; /* assumes fair_sched_class->next == idle_sched_class */ if (unlikely(!p)) p = idle_sched_class.pick_next_task(rq, prev); return p; } again: for_each_class(class) { p = class->pick_next_task(rq, prev); if (p) { if (unlikely(p == RETRY_TASK)) goto again; return p; } } BUG(); }(3)context_switch//进程上下文切换
context_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next) { struct mm_struct *mm, *oldmm; prepare_task_switch(rq, prev, next); mm = next->mm; oldmm = prev->active_mm; arch_start_context_switch(prev); if (!mm) { next->active_mm = oldmm; atomic_inc(&oldmm->mm_count); enter_lazy_tlb(oldmm, next); } else switch_mm(oldmm, mm, next); if (!prev->mm) { prev->active_mm = NULL; rq->prev_mm = oldmm; } spin_release(&rq->lock.dep_map, 1, _THIS_IP_); context_tracking_task_switch(prev, next); switch_to(prev, next, prev); barrier(); finish_task_switch(this_rq(), prev); }(4)switch_to//利用了prev和next两个参数：prev指向当前进程，next指向被调度的进程,switch_to内部是汇编代码,用以切换进程
#define switch_to(prev, next, last) do { unsigned long ebx, ecx, edx, esi, edi; asm volatile("pushfl\n\t" /* 保存当前进程的flags */ "pushl %