使用/proc/stat准确计算Linux中的CPU利用率
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Accurately Calculating CPU Utilization in Linux using /proc/stat
提问by Stephen Schaub
There are a number of posts and references on how to get CPU Utilization using statistics in /proc/stat. However, most of them use only four of the 7+ CPU stats (user, nice, system, and idle), ignoring the remaining jiffie CPU counts present in Linux 2.6 (iowait, irq, softirq).
有许多关于如何使用 /proc/stat 中的统计信息获取 CPU 利用率的帖子和参考资料。然而，他们中的大多数只使用了 7 个以上 CPU 统计信息中的四个（用户、nice、系统和空闲），忽略了 Linux 2.6 中存在的剩余 jiffie CPU 计数（iowait、irq、softirq）。
As an example, see Determining CPU utilization.
例如，请参阅确定 CPU 利用率。
My question is this: Are the iowait/irq/softirq numbers also counted in one of the first four numbers (user/nice/system/idle)? In other words, does the total jiffie count equal the sum of the first four stats? Or, is the total jiffie count equal to the sum of all 7 stats? If the latter is true, then a CPU utilization formula should take all of the numbers into account, like this:
我的问题是：iowait/irq/softirq 数字是否也计入前四个数字之一（user/nice/system/idle）？换句话说，总 jiffie 计数是否等于前四个统计数据的总和？或者，总 jiffie 计数是否等于所有 7 个统计数据的总和？如果后者为真，则 CPU 利用率公式应考虑所有数字，如下所示：
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
long double a[7],b[7],loadavg;
FILE *fp;
for(;;)
{
fp = fopen("/proc/stat","r");
fscanf(fp,"%*s %Lf %Lf %Lf %Lf",&a[0],&a[1],&a[2],&a[3],&a[4],&a[5],&a[6]);
fclose(fp);
sleep(1);
fp = fopen("/proc/stat","r");
fscanf(fp,"%*s %Lf %Lf %Lf %Lf",&b[0],&b[1],&b[2],&b[3],&b[4],&b[5],&b[6]);
fclose(fp);
loadavg = ((b[0]+b[1]+b[2]+b[4]+b[5]+b[6]) - (a[0]+a[1]+a[2]+a[4]+a[5]+a[6]))
/ ((b[0]+b[1]+b[2]+b[3]+b[4]+b[5]+b[6]) - (a[0]+a[1]+a[2]+a[3]+a[4]+a[5]+a[6]));
printf("The current CPU utilization is : %Lf\n",loadavg);
}
return(0);
}
采纳答案by Johnlcf
I think iowait/irq/softirq are not counted in one of the first 4 numbers. You can see the comment of irqtime_account_process_tick in kernel code for more detail:
我认为 iowait/irq/softirq 不计入前 4 个数字之一。您可以在内核代码中查看 irqtime_account_process_tick 的注释以了解更多详细信息：
(for Linux kernel 4.1.1)
（适用于Linux 内核 4.1.1）
2815 * Tick demultiplexing follows the order
2816 * - pending hardirq update <-- this is irq
2817 * - pending softirq update <-- this is softirq
2818 * - user_time
2819 * - idle_time <-- iowait is included in here, discuss below
2820 * - system time
2821 * - check for guest_time
2822 * - else account as system_time
For the idle time handling, see account_idle_time function:
空闲时间处理见 account_idle_time 函数：
2772 /*
2773 * Account for idle time.
2774 * @cputime: the cpu time spent in idle wait
2775 */
2776 void account_idle_time(cputime_t cputime)
2777 {
2778 u64 *cpustat = kcpustat_this_cpu->cpustat;
2779 struct rq *rq = this_rq();
2780
2781 if (atomic_read(&rq->nr_iowait) > 0)
2782 cpustat[CPUTIME_IOWAIT] += (__force u64) cputime;
2783 else
2784 cpustat[CPUTIME_IDLE] += (__force u64) cputime;
2785 }
If the cpu is idle AND there is some IO pending, it will count the time in CPUTIME_IOWAIT. Otherwise, it is count in CPUTIME_IDLE.
如果 cpu 空闲并且有一些 IO 挂起，它会在 CPUTIME_IOWAIT 中计算时间。否则，它在 CPUTIME_IDLE 中计数。
To conclude, I think the jiffies in irq/softirq should be counted as "busy" for cpu because it was actually handling some IRQ or soft IRQ. On the other hand, the jiffies in "iowait" should be counted as "idle" for cpu because it was not doing something but waiting for a pending IO to happen.
总而言之，我认为 irq/softirq 中的 jiffies 应该算作 cpu 的“忙”，因为它实际上是在处理一些 IRQ 或软 IRQ。另一方面，“iowait”中的 jiffies 应该算作 cpu 的“空闲”，因为它不是在做某事而是在等待挂起的 IO 发生。
回答by Massimo
from busybox, its top magic is:
来自busybox，它的顶级魔法是：
static const char fmt[] ALIGN1 = "cp%*s %llu %llu %llu %llu %llu %llu %llu %llu";
int ret;
if (!fgets(line_buf, LINE_BUF_SIZE, fp) || line_buf[0] != 'c' /* not "cpu" */)
return 0;
ret = sscanf(line_buf, fmt,
&p_jif->usr, &p_jif->nic, &p_jif->sys, &p_jif->idle,
&p_jif->iowait, &p_jif->irq, &p_jif->softirq,
&p_jif->steal);
if (ret >= 4) {
p_jif->total = p_jif->usr + p_jif->nic + p_jif->sys + p_jif->idle
+ p_jif->iowait + p_jif->irq + p_jif->softirq + p_jif->steal;
/* procps 2.x does not count iowait as busy time */
p_jif->busy = p_jif->total - p_jif->idle - p_jif->iowait;
}
