zircon的两种调度理解运维jason的笔记-

 zircon 实现两种调度机制，一种就是fair 其实现在fair_scheduler.cpp中，一种是基于时间片的其实现在sched.cpp 中，调度器的入口都在sche_reschedule()这个函数中。 例如fair的实现如下： void sched_reschedule() {     FairScheduler::Reschedule(); } fair的实现是一个cpp的类。 另一中sche_reschedule()的实现在sched.cpp 中，我们简单看下 void sched_reschedule() {             current_thread->state = THREAD_READY;      // idle thread doesn't go in the run queue     if (likely(!thread_is_idle(current_thread))) {  #可见会首先判断当前线程的时间片是否用尽，用尽的话，则加入到当前cpu 运行队列的末尾，否则就插入到head，这样下次调用这个函数的时候就会 优先调用这个函数           if (current_thread->remaining_time_slice > 0) {             insert_in_run_queue_head(curr_cpu, current_thread);         } else {             insert_in_run_queue_tail(curr_cpu, current_thread);         }     }      sched_resched_internal(); } void sched_resched_internal() {     thread_t* current_thread = get_current_thread();     uint cpu = arch_curr_cpu_num();           CPU_STATS_INC(reschedules);      // pick a new thread to run #从当前cpu 挑选一个thread 来运行，类似于linux的RR调度     thread_t* newthread = sched_get_top_thread(cpu);      DEBUG_ASSERT(newthread);      newthread->state = THREAD_RUNNING;      thread_t* oldthread = current_thread;     oldthread->preempt_pending = false;       #计算久进程的时间记账     zx_time_t now = current_time();      // account for time used on the old thread     DEBUG_ASSERT(now >= oldthread->last_started_running);     zx_duration_t old_runtime = zx_time_sub_time(now, oldthread->last_started_running);     oldthread->runtime_ns = zx_duration_add_duration(oldthread->runtime_ns, old_runtime);     oldthread->remaining_time_slice = zx_duration_sub_duration(         oldthread->remaining_time_slice, MIN(old_runtime, oldthread->remaining_time_slice));      // set up quantum for the new thread if it was consumed     if (newthread->remaining_time_slice == 0) {         newthread->remaining_time_slice = THREAD_INITIAL_TIME_SLICE;     }      newthread->last_started_running = now; #切换mmu     // see if we need to swap mmu context     if (newthread->aspace != oldthread->aspace) {         vmm_context_switch(oldthread->aspace, newthread->aspace);     } #进程切换     // do the low level context switch     final_context_switch(oldthread, newthread); }