更新时间片 -- scheduler_tick()

时钟中断处理程序中会调用函数scheduler_tick():

函数scheduler_tick()更新当前进程的time_slice;并根据time_slice的使用情况(剩余还是耗尽)，来做进一步处理.scheduler_tick(
) Keeps the time_slice counter of current up-to-date

void scheduler_tick(void)

{

int cpu = smp_processor_id();

runqueue_t *rq = this_rq();

task_t *p = current;

unsigned long long now = sched_clock();

update_cpu_clock(p, rq, now);

更新运行队列的最新时钟中断时间戳为当前时间

|----------------------------------|

| rq->timestamp_last_tick = now; |

|----------------------------------|

如果当前进程为本地CPU的swapper进程

|-------------------------------------------|

| if (p == rq->idle) { |

| if (wake_priority_sleeper(rq)) |

| goto out; |

| rebalance_tick(cpu, rq, SCHED_IDLE);|

| return; |

| } |

|-------------------------------------------|

如果当前进程不是活跃(active)进程

|---------------------------------|

| if (p->array != rq->active) { |

| set_tsk_need_resched(p);
|

| goto out; |

| } |

|---------------------------------|

spin_lock(&rq->lock);

如果当前进程是实时进程；如果调度策略为SCHED_RR，并且其时间片已经耗尽；为该进程重新计算时间片；清除first_time_slice域；设置task_struct.thread_info.flags域;将该任务插入其所在活跃队列的尾部.

|----------------------------------------------------------|

| if (rt_task(p))
{ |

| if ((p->policy == SCHED_RR) && !--p->time_slice) { |

| p->time_slice = task_timeslice(p);
|

| p->first_time_slice = 0; |

| set_tsk_need_resched(p);
|

| requeue_task(p,
rq->active); |

| } |

| goto out_unlock; |

| } |

|----------------------------------------------------------|

当前进程为普通进程，如果其时间片已经耗尽；将该进程从活跃队列中删除；设置task_struct.thread_info.flags域；重新计算动态优先级prio；重新计算时间片；清除first_time_slice域；如果过期队列为空，将更新 runqueue.expired_timestamp；Inserts
the current process either in the active set or in the expired set

|------------------------------------------------------------|

| if (!--p->time_slice) { |

| dequeue_task(p,
rq->active); |

| set_tsk_need_resched(p);
|

| p->prio = effective_prio(p);
|

| p->time_slice = task_timeslice(p); |

| p->first_time_slice = 0; |

| |

| if (!rq->expired_timestamp) |

| rq->expired_timestamp = jiffies; |

| if (!TASK_INTERACTIVE(p)
|| EXPIRED_STARVING(rq)) { |

| enqueue_task(p, rq->expired); |

| if (p->static_prio < rq->best_expired_prio) |

| rq->best_expired_prio = p->static_prio; |

| } else |

| enqueue_task(p, rq->active); |

|------------------------------------------------------------|

如果时间片没有耗尽，并且剩余时间片过长;则将该进程插入其所在队列的尾部；并设置task_struct.thread_info.flags域

if the time quantum is not exhausted (current->time_slice is not zero), checks whether the remaining time slice of the current process is too long.

|-----------------------------------------------------------------------------|

| } else { |

| if ( TASK_INTERACTIVE(p) && |

| !((task_timeslice(p) - p->time_slice) % TIMESLICE_GRANULARITY(p)) &&|

| (p->time_slice >= TIMESLICE_GRANULARITY(p)) && |

| (p->array == rq->active)) { |

| requeue_task(p, rq->active); |

| |

| set_tsk_need_resched(p); |

| } |

| } |

|-----------------------------------------------------------------------------|

out_unlock:

spin_unlock(&rq->lock);

out:

rebalance_tick(cpu, rq, NOT_IDLE);

}