v03.06 鸿蒙内核源码分析(时钟任务) | 触发调度谁的贡献最大 原创

/**
 * @ingroup los_config
 * Number of Ticks in one second
 */
#ifndef LOSCFG_BASE_CORE_TICK_PER_SECOND
#define LOSCFG_BASE_CORE_TICK_PER_SECOND 100 //默认每秒100次触发，当然这是可以改的
#endif
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/*
 * Description : Tick interruption handler
 *///节拍中断处理函数 ,鸿蒙默认10ms触发一次
LITE_OS_SEC_TEXT VOID OsTickHandler(VOID)
{
    //...
    OsTimesliceCheck();//进程和任务的时间片检查
    OsTaskScan(); /* task timeout scan *///任务扫描
#if (LOSCFG_BASE_CORE_SWTMR == YES)
    OsSwtmrScan();//定时器扫描,看是否有超时的定时器
#endif
}
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#ifndef LOSCFG_BASE_CORE_TIMESLICE_TIMEOUT
#define LOSCFG_BASE_CORE_TIMESLICE_TIMEOUT 2 //2个时间片,20ms
#endif
//检查进程和任务的时间片,如果没有时间片了直接调度
LITE_OS_SEC_TEXT VOID OsTimesliceCheck(VOID)
{
    LosTaskCB *runTask = NULL;
    LosProcessCB *runProcess = OsCurrProcessGet();//获取当前进程
    if (runProcess->policy != LOS_SCHED_RR) {//进程调度算法是否是抢占式
        goto SCHED_TASK;//进程不是抢占式调度直接去检查任务的时间片
    }

    if (runProcess->timeSlice != 0) {//进程还有时间片吗?
        runProcess->timeSlice--;//进程时间片减少一次
        if (runProcess->timeSlice == 0) {//没有时间片了
            LOS_Schedule();//进程时间片用完,发起调度
        }
    }

SCHED_TASK:
    runTask = OsCurrTaskGet();//获取当前任务
    if (runTask->policy != LOS_SCHED_RR) {//任务调度算法是否是抢占式
        return;//任务不是抢占式调度直接结束检查
    }

    if (runTask->timeSlice != 0) {//任务还有时间片吗?
        runTask->timeSlice--;//任务时间片也减少一次
        if (runTask->timeSlice == 0) {//没有时间片了
            LOS_Schedule();//任务时间片用完,发起调度
        }
    }
}
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LITE_OS_SEC_TEXT VOID OsTaskScan(VOID)
{
    SortLinkList *sortList = NULL;
    LosTaskCB *taskCB = NULL;
    BOOL needSchedule = FALSE;
    UINT16 tempStatus;
    LOS_DL_LIST *listObject = NULL;
    SortLinkAttribute *taskSortLink = NULL;

    taskSortLink = &OsPercpuGet()->taskSortLink;//获取任务的排序链表
    taskSortLink->cursor = (taskSortLink->cursor + 1) & OS_TSK_SORTLINK_MASK;
    listObject = taskSortLink->sortLink + taskSortLink->cursor;//只处理这个游标上的链表,因为系统对超时任务都已经规链表了.
 //当任务因超时而挂起时，任务块处于超时排序链接上,（每个cpu）和ipc（互斥锁、扫描电镜等）的块同时被唤醒
    /*不管是超时还是相应的ipc，它都在等待。现在使用synchronize sortlink precedure，因此整个任务扫描需要保护，防止另一个核心同时删除sortlink。
     * When task is pended with timeout, the task block is on the timeout sortlink
     * (per cpu) and ipc(mutex,sem and etc.)'s block at the same time, it can be waken
     * up by either timeout or corresponding ipc it's waiting.
     *
     * Now synchronize sortlink preocedure is used, therefore the whole task scan needs
     * to be protected, preventing another core from doing sortlink deletion at same time.
     */
    LOS_SpinLock(&g_taskSpin);

    if (LOS_ListEmpty(listObject)) {
        LOS_SpinUnlock(&g_taskSpin);
        return;
    }
    sortList = LOS_DL_LIST_ENTRY(listObject->pstNext, SortLinkList, sortLinkNode);//拿本次Tick对应链表的SortLinkList的第一个节点sortLinkNode
    ROLLNUM_DEC(sortList->idxRollNum);//滚动数--

    while (ROLLNUM(sortList->idxRollNum) == 0) {//找到时间到了节点,注意这些节点都是由定时器产生的,
        LOS_ListDelete(&sortList->sortLinkNode);
        taskCB = LOS_DL_LIST_ENTRY(sortList, LosTaskCB, sortList);//拿任务,这里的任务都是超时任务
        taskCB->taskStatus &= ~OS_TASK_STATUS_PEND_TIME;
        tempStatus = taskCB->taskStatus;
        if (tempStatus & OS_TASK_STATUS_PEND) {
            taskCB->taskStatus &= ~OS_TASK_STATUS_PEND;
#if (LOSCFG_KERNEL_LITEIPC == YES)
            taskCB->ipcStatus &= ~IPC_THREAD_STATUS_PEND;
#endif
            taskCB->taskStatus |= OS_TASK_STATUS_TIMEOUT;
            LOS_ListDelete(&taskCB->pendList);
            taskCB->taskSem = NULL;
            taskCB->taskMux = NULL;
        } else {
            taskCB->taskStatus &= ~OS_TASK_STATUS_DELAY;
        }

        if (!(tempStatus & OS_TASK_STATUS_SUSPEND)) {
            OS_TASK_SCHED_QUEUE_ENQUEUE(taskCB, OS_PROCESS_STATUS_PEND);
            needSchedule = TRUE;
        }

        if (LOS_ListEmpty(listObject)) {
            break;
        }

        sortList = LOS_DL_LIST_ENTRY(listObject->pstNext, SortLinkList, sortLinkNode);
    }

    LOS_SpinUnlock(&g_taskSpin);

    if (needSchedule != FALSE) {//需要调度
        LOS_MpSchedule(OS_MP_CPU_ALL);//核间通讯,给所有CPU发送调度信号
        LOS_Schedule();//开始调度
    }
}
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/*
 * Description: Tick interrupt interface module of software timer
 * Return     : LOS_OK on success or error code on failure
 *///OsSwtmrScan 由系统时钟中断处理函数调用
LITE_OS_SEC_TEXT VOID OsSwtmrScan(VOID)//扫描定时器,如果碰到超时的,就放入超时队列
{
    SortLinkList *sortList = NULL;
    SWTMR_CTRL_S *swtmr = NULL;
    SwtmrHandlerItemPtr swtmrHandler = NULL;
    LOS_DL_LIST *listObject = NULL;
    SortLinkAttribute* swtmrSortLink = &OsPercpuGet()->swtmrSortLink;//拿到当前CPU的定时器链表

    swtmrSortLink->cursor = (swtmrSortLink->cursor + 1) & OS_TSK_SORTLINK_MASK;
    listObject = swtmrSortLink->sortLink + swtmrSortLink->cursor;
 //由于swtmr是在特定的sortlink中，所以需要很小心的处理它,但其他CPU Core仍然有机会处理它，比如停止计时器
    /*
     * it needs to be carefully coped with, since the swtmr is in specific sortlink
     * while other cores still has the chance to process it, like stop the timer.
     */
    LOS_SpinLock(&g_swtmrSpin);

    if (LOS_ListEmpty(listObject)) {
        LOS_SpinUnlock(&g_swtmrSpin);
        return;
    }
    sortList = LOS_DL_LIST_ENTRY(listObject->pstNext, SortLinkList, sortLinkNode);
    ROLLNUM_DEC(sortList->idxRollNum);

    while (ROLLNUM(sortList->idxRollNum) == 0) {
        sortList = LOS_DL_LIST_ENTRY(listObject->pstNext, SortLinkList, sortLinkNode);
        LOS_ListDelete(&sortList->sortLinkNode);
        swtmr = LOS_DL_LIST_ENTRY(sortList, SWTMR_CTRL_S, stSortList);

        swtmrHandler = (SwtmrHandlerItemPtr)LOS_MemboxAlloc(g_swtmrHandlerPool);//取出一个可用的软时钟处理项
        if (swtmrHandler != NULL) {
            swtmrHandler->handler = swtmr->pfnHandler;
            swtmrHandler->arg = swtmr->uwArg;

            if (LOS_QueueWrite(OsPercpuGet()->swtmrHandlerQueue, swtmrHandler, sizeof(CHAR *), LOS_NO_WAIT)) {
                (VOID)LOS_MemboxFree(g_swtmrHandlerPool, swtmrHandler);
            }
        }

        if (swtmr->ucMode == LOS_SWTMR_MODE_ONCE) {
            OsSwtmrDelete(swtmr);

            if (swtmr->usTimerID < (OS_SWTMR_MAX_TIMERID - LOSCFG_BASE_CORE_SWTMR_LIMIT)) {
                swtmr->usTimerID += LOSCFG_BASE_CORE_SWTMR_LIMIT;
            } else {
                swtmr->usTimerID %= LOSCFG_BASE_CORE_SWTMR_LIMIT;
            }
        } else if (swtmr->ucMode == LOS_SWTMR_MODE_NO_SELFDELETE) {
            swtmr->ucState = OS_SWTMR_STATUS_CREATED;
        } else {
            swtmr->ucOverrun++;
            OsSwtmrStart(swtmr);
        }

        if (LOS_ListEmpty(listObject)) {
            break;
        }

        sortList = LOS_DL_LIST_ENTRY(listObject->pstNext, SortLinkList, sortLinkNode);
    }

    LOS_SpinUnlock(&g_swtmrSpin);
}
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//调度算法的实现
VOID OsSchedResched(VOID)
{
    LosTaskCB *runTask = NULL;
    LosTaskCB *newTask = NULL;
    LosProcessCB *runProcess = NULL;
    LosProcessCB *newProcess = NULL;
    LOS_ASSERT(LOS_SpinHeld(&g_taskSpin));//必须持有任务自旋锁,自旋锁是不是进程层面去抢锁,而是CPU各自核之间去争夺锁

    if (!OsPreemptableInSched()) {//是否置了重新调度标识位
        return;
    }
    runTask = OsCurrTaskGet();//获取当前任务
    newTask = OsGetTopTask();//获取优先级最最最高的任务
    /* always be able to get one task */
    LOS_ASSERT(newTask != NULL);//不能没有需调度的任务
    if (runTask == newTask) {//当前任务就是最高任务,那还调度个啥的,直接退出.
        return;
    }
    runTask->taskStatus &= ~OS_TASK_STATUS_RUNNING;//当前任务状态位置成不在运行状态
    newTask->taskStatus |= OS_TASK_STATUS_RUNNING;//最高任务状态位置成在运行状态
    runProcess = OS_PCB_FROM_PID(runTask->processID);//通过进程ID索引拿到进程实体
    newProcess = OS_PCB_FROM_PID(newTask->processID);//同上
    OsSchedSwitchProcess(runProcess, newProcess);//切换进程,里面主要涉及进程空间的切换,也就是MMU的上下文切换.
#if (LOSCFG_KERNEL_SMP == YES)//CPU多核的情况
    /* mask new running task's owner processor */
    runTask->currCpu = OS_TASK_INVALID_CPUID;//当前任务不占用CPU
    newTask->currCpu = ArchCurrCpuid();//让新任务占用CPU
#endif
    (VOID)OsTaskSwitchCheck(runTask, newTask);//切换task的检查
#if (LOSCFG_KERNEL_SCHED_STATISTICS == YES)
    OsSchedStatistics(runTask, newTask);
#endif
    if ((newTask->timeSlice == 0) && (newTask->policy == LOS_SCHED_RR)) {//没有时间片且是抢占式调度的方式,注意 非抢占式都不需要时间片的.
        newTask->timeSlice = LOSCFG_BASE_CORE_TIMESLICE_TIMEOUT;//给新任务时间片 默认 20ms
    }
    OsCurrTaskSet((VOID*)newTask);//设置新的task为CPU核的当前任务
    if (OsProcessIsUserMode(newProcess)) {//用户模式下会怎么样?
        OsCurrUserTaskSet(newTask->userArea);//设置task栈空间
    }
    /* do the task context switch */
    OsTaskSchedule(newTask, runTask);//切换任务上下文,注意OsTaskSchedule是一个汇编函数 见于 los_dispatch.s
}
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