进程调度API之set_user_nice

void set_user_nice(struct task_struct *p, long nice)用于设置进程的nice值.其使用的例程如下：static int kmemleak_scan_thread(void *arg){static int first_run = 1;pr_info("Automatic memory scanning thread started\n");set_user_nice(current, 10);}其源码分析如下：void set_user_nice(struct task_struct *p, long nice){bool queued, running;int old_prio, delta;struct rq_flags rf;struct rq *rq;#如果当前task的nice值已经等于要设置的nice值，就直接退出#从这里可以看出nice值的范围在-20~19 之间if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)return;/* * We have to be careful, if called from sys_setpriority(), * the task might be in the middle of scheduling on another CPU. */rq = task_rq_lock(p, &rf);update_rq_clock(rq);/* * The RT priorities are set via sched_setscheduler(), but we still * allow the 'normal' nice value to be set - but as expected * it wont have any effect on scheduling until the task is * SCHED_DEADLINE, SCHED_FIFO or SCHED_RR: */#如果当前是实时进程，这里也可以看出实时进程的的调度策略可以分为deadline/fifo/rr.#针对实时进程设置nice值其实是没有作用的，但是这里还是将nice值转成优先级后设置到p->static_prio if (task_has_dl_policy(p) || task_has_rt_policy(p)) {p->static_prio = NICE_TO_PRIO(nice);goto out_unlock;}queued = task_on_rq_queued(p);running = task_current(rq, p);if (queued)dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);if (running)put_prev_task(rq, p);#将nice值转成优先级设置到static_prio 中，#define NICE_TO_PRIO(nice)((nice) + DEFAULT_PRIO)#这里的DEFAULT_PRIO 值经过计算是120.#从这里也可以看出优先级转nice值应该是减去DEFAULT_PRIO #define PRIO_TO_NICE(prio)((prio) - DEFAULT_PRIO)p->static_prio = NICE_TO_PRIO(nice);set_load_weight(p);old_prio = p->prio;p->prio = effective_prio(p);delta = p->prio - old_prio;#如果要设置的nice的task在queue中if (queued) {enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);/* * If the task increased its priority or is running and * lowered its priority, then reschedule its CPU: */#如果增大优先级且task正在运行或者减小优先级的话，则重新调度rq。if (delta < 0 || (delta > 0 && task_running(rq, p)))resched_curr(rq);}#如果要设置nice值的task正在运行，由于我们这里改变了p的优先级，则重新指定task的rq.if (running)set_curr_task(rq, p);out_unlock:task_rq_unlock(rq, p, &rf);}