set_user_nice

set_user_nice函数功能：设置某一进程的NICE值，其NICE值的计算是根据进程的静态优先级（task_struct->static_prio），直接通过set_user_nice函数更改进程的静态优先级。

内核源码

void set_user_nice(struct task_struct *p, long nice)
{
	bool queued, running;
	int old_prio;
	struct rq_flags rf;
	struct rq *rq;

	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:
	 */
	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);

	p->static_prio = NICE_TO_PRIO(nice);
	set_load_weight(p, true);
	old_prio = p->prio;
	p->prio = effective_prio(p);

	if (queued)
		enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
	if (running)
		set_next_task(rq, p);

	/*
	 * If the task increased its priority or is running and
	 * lowered its priority, then reschedule its CPU:
	 */
	p->sched_class->prio_changed(rq, p, old_prio);

out_unlock:
	task_rq_unlock(rq, p, &rf);
}
EXPORT_SYMBOL(set_user_nice);

使用示例

#include <linux/module.h>
#include <linux/pid.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kthread.h>

static int MyThreadFunc(void* argc) {

	printk("Prompt:kernel thread PID : %d.\n", current->pid);

	printk("Prompt:kernel thread static_prio : %d.\n", current->static_prio);

	printk("Prompt:kernel thread nice : %d.\n", task_nice(current));

	return 0;
}

static int __init SetUserNiceInit(void) {

	struct task_struct* new_task = NULL;

	new_task = kthread_create_on_node(MyThreadFunc, NULL, -1, "setusernice.c");

	printk("Prompt:new thread nice : %d.\n", task_nice(new_task));

	printk("Prompt:new thread static_prio : %d.\n", new_task->static_prio);

	printk("Prompt:new thread prio : %d.\n", new_task->prio);

	set_user_nice(new_task, 16);

	printk("Prompt:new thread nice : %d.\n", task_nice(new_task));

	printk("Prompt:new thread static_prio : %d.\n", new_task->static_prio);

	printk("Prompt:new thread prio : %d.\n", new_task->prio);

	return 0;
}

static void __exit SetUserNiceExit(void) {

	printk("Prompt:exit kernel.\n");
}

module_init(SetUserNiceInit);
module_exit(SetUserNiceExit);

运行结果