zircon的两种调度理解

编程基础 • 2024-12-26 08:06 • 阅读 13
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); }
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zircon的两种调度理解

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