新手學堂：Linux操作系統關於負載的定義

//kernel/timer.c

1254 active_tasks = count_active_tasks();

1256 CALC_LOAD(avenrun[0], EXP_1, active_tasks);
1257 CALC_LOAD(avenrun[1], EXP_5, active_tasks);
1258 CALC_LOAD(avenrun[2], EXP_15, active_tasks);

//include/linux/sched.h
110 #define FSHIFT 11 /* nr of bits of precision */
111 #define FIXED_1 (1<
112 #define LOAD_FREQ (5*HZ) /* 5 sec intervals */
113 #define EXP_1 1884 /* 1/exp(5sec/1min) as fixed-point */
114 #define EXP_5 2014 /* 1/exp(5sec/5min) */
115 #define EXP_15 2037 /* 1/exp(5sec/15min) */

117 #define CALC_LOAD(load,exp,n) 
118 load *= exp; 
119 load += n*(FIXED_1-exp); 
120 load >>= FSHIFT; 

　　load(t) = ( load(t-1)*exp(i) + n(t)*(2048-exp(i)) ) / 2048
　　load(t-1)為上次計算出的結果
　　n(t)為t時刻的活動進程數 
　　計算方式是累加各個CPU的運行隊列中running和uninterruptible的值　再乘以2048
　　計算方式如下：

1946 unsigned long nr_active(void)
1947 {
1948 unsigned long i, running = 0, uninterruptible = 0;
1949
1950 for_each_online_cpu(i) {
1951 running += cpu_rq(i)->nr_running;
1952 uninterruptible += cpu_rq(i)->nr_uninterruptible;
1953 }
1954
1955 if (unlikely((long)uninterruptible < 0))
1956 uninterruptible = 0;
1957
1958 return running + uninterruptible;
1959 }


1226 static unsigned long count_active_tasks(void)
1227 {
1228 return nr_active() * FIXED_1;
1229 } 


　　exp(1) = 1884
　　exp(5) = 2014
　　exp(15) = 2037
　　exp(i) = 2048 * e^(-1/12/i)