linux cpu占用率

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本文详细解析了Linux系统中CPU占用率中wa和ni两个指标的含义。wa表示I/O等待时间，当wa为100%时，意味着CPU在执行idle进程，等待I/O操作完成。ni则与进程的nice值有关，它记录了用户态下优先级被调整的进程所消耗的时间。通过ni，系统将nice值转换为静态优先级，用于调度决策。

cpu 占用率之 wa

wa 占用率为100%时，并不是 cpu 在忙转，此时cpu 一直执行idle 进程。

void __sched io_schedule(void)
{
struct rq *rq = raw_rq();

delayacct_blkio_start();
atomic_inc(&rq->nr_iowait);
current->in_iowait = 1;
schedule();
current->in_iowait = 0;
atomic_dec(&rq->nr_iowait);
delayacct_blkio_end();
}

update_process_times->account_process_tick

void account_process_tick(struct task_struct *p, int user_tick)
{
cputime_t one_jiffy_scaled = cputime_to_scaled(cputime_one_jiffy);
struct rq *rq = this_rq();

if (user_tick)
account_user_time(p, cputime_one_jiffy, one_jiffy_scaled);
else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET))
account_system_time(p, HARDIRQ_OFFSET, cputime_one_jiffy,
one_jiffy_scaled);
else
account_idle_time(cputime_one_jiffy);
}

void account_idle_time(cputime_t cputime)
{
struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
cputime64_t cputime64 = cputime_to_cputime64(cputime);
struct rq *rq = this_rq();

if (atomic_read(&rq->nr_iowait) > 0)
cpustat->iowait = cputime64_add(cpustat->iowait, cputime64);
else
cpustat->idle = cputime64_add(cpustat->idle, cputime64);
}

s3c2410_timer_interrupt ->timer_tick ->

void timer_tick(void)
{
profile_tick(CPU_PROFILING);
do_leds();
do_set_rtc();
write_seqlock(&xtime_lock);
do_timer(1);
write_sequnlock(&xtime_lock);
#ifndef CONFIG_SMP
update_process_times(user_mode(get_irq_regs()));
#endif
}

void do_timer(unsigned long ticks)
{
jiffies_64 += ticks;
update_wall_time();
calc_global_load();
}

cpu 占用率之 ni :

tmp = cputime_to_cputime64(cputime);
if (TASK_NICE(p) > 0)
cpustat->nice = cputime64_add(cpustat->nice, tmp);
else
cpustat->user = cputime64_add(cpustat->user, tmp);

/*
* 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)