cpu负载的探讨

/* Variables and functions for calc_load */
static atomic_long_t calc_load_tasks;
static unsigned long calc_load_update;
unsigned long avenrun[3];
EXPORT_SYMBOL(avenrun);
 
/**
 * get_avenrun - get the load average array
 * @loads: pointer to dest load array
 * @offset: offset to add
 * @shift: shift count to shift the result left
 *
 * These values are estimates at best, so no need for locking.
 */
void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
{
loads[0] = (avenrun[0] + offset) << shift;
loads[1] = (avenrun[1] + offset) << shift;
loads[2] = (avenrun[2] + offset) << shift;
}
 
static unsigned long
calc_load(unsigned long load, unsigned long exp, unsigned long active)
{
load *= exp;
load += active * (FIXED_1 - exp);
return load >> FSHIFT;
}
 
/*
 * calc_load - update the avenrun load estimates 10 ticks after the
 * CPUs have updated calc_load_tasks.
 */
void calc_global_load(void)
{
unsigned long upd = calc_load_update + 10;
long active;
 
if (time_before(jiffies, upd))
return;
 
active = atomic_long_read(&calc_load_tasks);
active = active > 0 ? active * FIXED_1 : 0;
 
avenrun[0] = calc_load(avenrun[0], EXP_1, active);
avenrun[1] = calc_load(avenrun[1], EXP_5, active);
avenrun[2] = calc_load(avenrun[2], EXP_15, active);
 
calc_load_update += LOAD_FREQ;
}
 
/*
 * Either called from update_cpu_load() or from a cpu going idle
 */
static void calc_load_account_active(struct rq *this_rq)
{
long nr_active, delta;
 
nr_active = this_rq->nr_running;  //记录在cpu上运行的进程数
nr_active += (long) this_rq->nr_uninterruptible;  //记录不可中断的进程数
 
if (nr_active != this_rq->calc_load_active) {
delta = nr_active - this_rq->calc_load_active;
this_rq->calc_load_active = nr_active;
atomic_long_add(delta, &calc_load_tasks);
}
}