linux kernel goodness计算分析

今天早上8点过出去买了点东西，回来就赶紧打开source insight看kernel code，跟妹子聊了会天，现在开始分析：

/**这个函数是来确定如何描述一个进程返回值：-1000：从不选择这个0：过期进程，重新计算计数值（但它仍旧可能被选中）正值：goodness值（越大越好）+1000：实时进程，选择这个*/static inline int goodness(struct task_struct * p, int this_cpu, struct mm_struct *this_mm){     int weight;     /*     * select the current process after every other     * runnable process, but before the idle thread.     * Also, dont trigger a counter recalculation.     */     weight = -1;     if (p->policy & SCHED_YIELD) //p->policy表示进程的调度策略，SCHED_YIELD是一种策略，是为了从小分配而让出CPU，就是直接返回啦！#define SCHED_YIELD          0x10          goto out;     /*     * Non-RT process - normal case first.     */     //SCHED_OTHER表示分时调度策略     if (p->policy == SCHED_OTHER) {          /*          * Give the process a first-approximation goodness value          * according to the number of clock-ticks it has left.          *          * Don't do any other calculations if the time slice is          * over..          */          weight = p->counter;          if (!weight)               goto out;              #ifdef CONFIG_SMP          /* Give a largish advantage to the same processor...   */          /* (this is equivalent to penalizing other processors) */          if (p->processor == this_cpu)               weight += PROC_CHANGE_PENALTY;#endif          /* .. and a slight advantage to the current MM */          if (p->mm == this_mm || !p->mm)               weight += 1;          weight += 20 - p->nice;          goto out;     }     /*     * Realtime process, select the first one on the     * runqueue (taking priorities within processes     * into account).     */     weight = 1000 + p->rt_priority;out:     return weight;}这个函数比较简单吧，就是计算进程goodness值，对于分时策略，会对一些情况weight有些加成；实时进程直接就给最大了。

其实如果木有神马ATT汇编，内核源码看起来还是很爽的，只是写了一个函数，今天计划把进程调度看完，跟书同步吧，至少把书上的字看完呢！