\linux\include\linux\sched.h中定义的有关频率，load average的相关常数与变量

#define HZ 100  //定义时钟频率，两个时钟间隔时间为10ms
/** These are the constant used to fake the fixed-point load-average* counting. Some notes:                                                                       *  - 11 bit fractions expand to 22 bits by the multiplies: this gives 11bit*    a load-average precision of 10 bits integer + 11 bits fractional*  - if you want to count load-averages more often, you need more*    precision, or rounding will get you. With 2-second counting freq,*    the EXP_n values would be 1981, 2034 and 2043 if still using only*    11 bit fractions.*/
extern unsigned long avenrun[];     /* Load averages */#define FSHIFT       11      /* nr of bits of precision */
#define FIXED_1     (1<<FSHIFT)   /* 1.0 as fixed-point */
#define LOAD_FREQ   (5*HZ)      /* 5 sec intervals */
#define EXP_1       1884        /* 1/exp(5sec/1min) as fixed-point */
#define EXP_5       2014        /* 1/exp(5sec/5min) */
#define EXP_15      2037        /* 1/exp(5sec/15min) */
#define CALC_LOAD(load,exp,n) \    //n=active_tasks活动进程数 ，load各个exp计算得到的average loadload *= exp; \load += n*(FIXED_1-exp); \load >>= FSHIFT;

load=(exp*load+n*(2048-exp))>>11。由这个式子来看，所谓的load只与当前活跃进程数有关。

\linux-2.4.x\kernel\timer.c中定义load average的计算函数。
unsigned long avenrun[3];static inline void calc_load(unsigned long ticks)
{unsigned long active_tasks; /* fixed-point */static int count = LOAD_FREQ;count -= ticks;if (count < 0) {count += LOAD_FREQ;active_tasks = count_active_tasks();CALC_LOAD(avenrun[0], EXP_1, active_tasks);CALC_LOAD(avenrun[1], EXP_5, active_tasks);CALC_LOAD(avenrun[2], EXP_15, active_tasks);}
}

\linux-2.4.x\fs\proc\proc_misc.c中定义使用uptime命令时调用load average显示函数的实现方式

static int loadavg_read_proc(char *page, char **start, off_t off,int count, int *eof, void *data)
{int a, b, c;int len;a = avenrun[0] + (FIXED_1/200);b = avenrun[1] + (FIXED_1/200);c = avenrun[2] + (FIXED_1/200);len = sprintf(page,"%d.%02d %d.%02d %d.%02d %d/%d %d\n",LOAD_INT(a), LOAD_FRAC(a),LOAD_INT(b), LOAD_FRAC(b),LOAD_INT(c), LOAD_FRAC(c),nr_running, nr_threads, last_pid);return proc_calc_metrics(page, start, off, count, eof, len);
}

http://www.yeeyan.org/articles/view/79184/37314