1. 进程的nice值与static_prio之间的转换关系
/*
* Convert user-nice values [ -20 ... 0 ... 19 ]
* to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
* and back.
*/
#define NICE_TO_PRIO(nice) (MAX_RT_PRIO + (nice) + 20)
#define PRIO_TO_NICE(prio) ((prio) - MAX_RT_PRIO - 20)
#define TASK_NICE(p) PRIO_TO_NICE((p)->static_prio)
2. 进程的用户优先级值与static_prio之间的转换关系
/*
* 'User priority' is the nice value converted to something we
* can work with better when scaling various scheduler parameters,
* it's a [ 0 ... 39 ] range.
*/
#define USER_PRIO(p) ((p)-MAX_RT_PRIO)
#define TASK_USER_PRIO(p) USER_PRIO((p)->static_prio)
#define MAX_USER_PRIO (USER_PRIO(MAX_PRIO))
说明：MAX_RT_PRIO为100，MAX_PRIO为140，即可计算出MAX_USER_PRIO=40
3. 时间片与进程优先级的关系
#define DEF_TIMESLICE (100 * HZ / 1000) //默认时间片是100ms
/*
* task_timeslice() scales user-nice values [ -20 ... 0 ... 19 ]
* to time slice values: [800ms ... 100ms ... 5ms]
*
* The higher a thread's priority, the bigger timeslices
* it gets during one round of execution. But even the lowest
* priority thread gets MIN_TIMESLICE worth of execution time.
*/
#define SCALE_PRIO(x, prio) \
max(x * (MAX_PRIO - prio) / (MAX_USER_PRIO/2), MIN_TIMESLICE)
static unsigned int task_timeslice(task_t *p)
{
if (p->static_prio < NICE_TO_PRIO(0))
return SCALE_PRIO(DEF_TIMESLICE*4, p->static_prio);
else
return SCALE_PRIO(DEF_TIMESLICE, p->static_prio);
}
说明：
当进程的静态优先级<120时，时间片=400*(140-prio)/20;
当进程的静态优先级>=120时，时间片=100*(140-prio)/20;
结论：进程的时间片与其静态优先级(static_prio)相关，在运行队列中的位置与其实时优先级相关(prio)。