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Linux中計算特定CPU使用率案例詳解

發(fā)布日期：2021-12-18 00:39 | 文章來源：CSDN

Linux中計算特定CPU使用率 需求解決方案拓展參考

需求

在Linux中可以通過top指令查看某一進(jìn)程占用的CPU情況，也可以查看某一個CPU使用率情況（先top指令，然后按數(shù)字“1”鍵即可顯示每一個CPU的使用情況），如下圖：

而我們的需求是：如何得到一個CPU的占用率呢？

解決方案

1. 背景知識

在/proc/stat中可以查看每一個CPU的使用情況的，如下圖：

其中cpu(0/1/2/…)后面的那十個數(shù)字含義如下：

/proc/stat
kernel/system statistics.  Varies with architecture.  
Common entries include:
  user nice system idle iowait  irq  softirq steal guest guest_nice
cpu  4705 356  584 369923 23  0 0  0  0
cpu0 1393280 32966 572056 13343292 6130 0 17875 0 23933 0
The amount of time, measured in units of USER_HZ
(1/100ths of a second on most architectures, use
sysconf(_SC_CLK_TCK) to obtain the right value), that
the system ("cpu" line) or the specific CPU ("cpuN"
line) spent in various states:
user(1) Time spent in user mode.
nice(2) Time spent in user mode with low priority
 (nice).
system (3) Time spent in system mode.
idle(4) Time spent in the idle task.  This value
 should be USER_HZ times the second entry in the
 /proc/uptime pseudo-file.
iowait (since Linux 2.5.41)
 (5) Time waiting for I/O to complete.  This
 value is not reliable, for the following rea‐
 sons:
 1. The CPU will not wait for I/O to complete;
 iowait is the time that a task is waiting for
 I/O to complete.  When a CPU goes into idle
 state for outstanding task I/O, another task
 will be scheduled on this CPU.
 2. On a multi-core CPU, the task waiting for I/O
 to complete is not running on any CPU, so the
 iowait of each CPU is difficult to calculate.
 3. The value in this field may decrease in cer‐
 tain conditions.
irq (since Linux 2.6.0-test4)
 (6) Time servicing interrupts.
softirq (since Linux 2.6.0-test4)
 (7) Time servicing softirqs.
steal (since Linux 2.6.11)
 (8) Stolen time, which is the time spent in
 other operating systems when running in a virtu‐
 alized environment
guest (since Linux 2.6.24)
 (9) Time spent running a virtual CPU for guest
 operating systems under the control of the Linux
 kernel.
guest_nice (since Linux 2.6.33)
 (10) Time spent running a niced guest (virtual
 CPU for guest operating systems under the con‐
 trol of the Linux kernel).

2.計算具體CPU使用率

有了上面的背景知識，接下來我們就可以計算具體CPU的使用情況了。具體計算方式如下：

Total CPU time since boot = user+nice+system+idle+iowait+irq+softirq+steal
Total CPU Idle time since boot = idle + iowait
Total CPU usage time since boot = Total CPU time since boot - Total CPU Idle time since boot
Total CPU percentage = Total CPU usage time since boot/Total CPU time since boot * 100%

有了上面的計算公式，計算某一CPU使用率或者系統(tǒng)總的CPU占用率也就是不難了。
示例：計算系統(tǒng)整體CPU占用情況
首先從/proc/stat中獲取 t1時刻系統(tǒng)總體的user、nice、system、idle、iowait、irq、softirq、steal、guest、guest_nice的值，得到此時Total CPU time since boot（記為total1）和 Total CPU idle time since boot(記為idle1)。
其次，從/proc/stat中獲取t2時刻系統(tǒng)總的Total CPU time since boot（記為total2）和Total CPU idle time since boot（記為idle2）。（方法同上一步）
最后，計算t2與t1之間系統(tǒng)總的CPU使用情況。也就是：
CPU percentage between t1 and t2 = (（total2-total1）-（idle2-idle1））/（total2-total1）* 100%
其中， (（total2-total1）-（idle2-idle1））實際上就是t1與t2時刻之間系統(tǒng)CPU被占用的時間（總時間 - 空閑時間）。
下面是一段計算時間段內(nèi)CPU被占用情況的腳本：

#!/bin/bash
# by Paul Colby (http://colby.id.au), no rights reserved ;)
PREV_TOTAL=0
PREV_IDLE=0
while true; do
  # Get the total CPU statistics, discarding the 'cpu ' prefix.
  CPU=(`sed -n 's/^cpu\s//p' /proc/stat`)
  IDLE=${CPU[3]} # Just the idle CPU time.
  # Calculate the total CPU time.
  TOTAL=0
  for VALUE in "${CPU[@]}"; do
 let "TOTAL=$TOTAL+$VALUE"
  done
  # Calculate the CPU usage since we last checked.
  let "DIFF_IDLE=$IDLE-$PREV_IDLE"
  let "DIFF_TOTAL=$TOTAL-$PREV_TOTAL"
  let "DIFF_USAGE=(1000*($DIFF_TOTAL-$DIFF_IDLE)/$DIFF_TOTAL+5)/10"
  echo -en "\rCPU: $DIFF_USAGE%  \b\b"
  # Remember the total and idle CPU times for the next check.
  PREV_TOTAL="$TOTAL"
  PREV_IDLE="$IDLE"
  # Wait before checking again.
  sleep 1
done

拓展

在內(nèi)核中，關(guān)于/proc/stat中文件的實現(xiàn)函數(shù)如下：

附注：內(nèi)核版本3.14.69，文件為 /fs/proc/stat.c
#include <linux/cpumask.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/irqnr.h>
#include <asm/cputime.h>
#include <linux/tick.h>
#ifndef arch_irq_stat_cpu
#define arch_irq_stat_cpu(cpu) 0
#endif
#ifndef arch_irq_stat
#define arch_irq_stat() 0
#endif
#ifdef arch_idle_time
static cputime64_t get_idle_time(int cpu)
{
	cputime64_t idle;
	idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE];
	if (cpu_online(cpu) && !nr_iowait_cpu(cpu))
		idle += arch_idle_time(cpu);
	return idle;
}
static cputime64_t get_iowait_time(int cpu)
{
	cputime64_t iowait;
	iowait = kcpustat_cpu(cpu).cpustat[CPUTIME_IOWAIT];
	if (cpu_online(cpu) && nr_iowait_cpu(cpu))
		iowait += arch_idle_time(cpu);
	return iowait;
}
#else
static u64 get_idle_time(int cpu)
{
	u64 idle, idle_time = -1ULL;
	if (cpu_online(cpu))
		idle_time = get_cpu_idle_time_us(cpu, NULL);
	if (idle_time == -1ULL)
		/* !NO_HZ or cpu offline so we can rely on cpustat.idle */
		idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE];
	else
		idle = usecs_to_cputime64(idle_time);
	return idle;
}
static u64 get_iowait_time(int cpu)
{
	u64 iowait, iowait_time = -1ULL;
	if (cpu_online(cpu))
		iowait_time = get_cpu_iowait_time_us(cpu, NULL);
	if (iowait_time == -1ULL)
		/* !NO_HZ or cpu offline so we can rely on cpustat.iowait */
		iowait = kcpustat_cpu(cpu).cpustat[CPUTIME_IOWAIT];
	else
		iowait = usecs_to_cputime64(iowait_time);
	return iowait;
}
#endif
static int show_stat(struct seq_file *p, void *v)
{
	int i, j;
	unsigned long jif;
	u64 user, nice, system, idle, iowait, irq, softirq, steal;
	u64 guest, guest_nice;
	u64 sum = 0;
	u64 sum_softirq = 0;
	unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
	struct timespec boottime;
	user = nice = system = idle = iowait =
		irq = softirq = steal = 0;
	guest = guest_nice = 0;
	getboottime(&boottime);
	jif = boottime.tv_sec;
	for_each_possible_cpu(i) {
		user += kcpustat_cpu(i).cpustat[CPUTIME_USER];
		nice += kcpustat_cpu(i).cpustat[CPUTIME_NICE];
		system += kcpustat_cpu(i).cpustat[CPUTIME_SYSTEM];
		idle += get_idle_time(i);
		iowait += get_iowait_time(i);
		irq += kcpustat_cpu(i).cpustat[CPUTIME_IRQ];
		softirq += kcpustat_cpu(i).cpustat[CPUTIME_SOFTIRQ];
		steal += kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
		guest += kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
		guest_nice += kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
		sum += kstat_cpu_irqs_sum(i);
		sum += arch_irq_stat_cpu(i);
		for (j = 0; j < NR_SOFTIRQS; j++) {
			unsigned int softirq_stat = kstat_softirqs_cpu(j, i);
			per_softirq_sums[j] += softirq_stat;
			sum_softirq += softirq_stat;
		}
	}
	sum += arch_irq_stat();
	seq_puts(p, "cpu ");
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(nice));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(system));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(idle));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(iowait));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(irq));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(softirq));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(steal));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
	seq_putc(p, '\n');
	for_each_online_cpu(i) {
		/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
		user = kcpustat_cpu(i).cpustat[CPUTIME_USER];
		nice = kcpustat_cpu(i).cpustat[CPUTIME_NICE];
		system = kcpustat_cpu(i).cpustat[CPUTIME_SYSTEM];
		idle = get_idle_time(i);
		iowait = get_iowait_time(i);
		irq = kcpustat_cpu(i).cpustat[CPUTIME_IRQ];
		softirq = kcpustat_cpu(i).cpustat[CPUTIME_SOFTIRQ];
		steal = kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
		guest = kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
		guest_nice = kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
		seq_printf(p, "cpu%d", i);
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(nice));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(system));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(idle));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(iowait));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(irq));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(softirq));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(steal));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
		seq_putc(p, '\n');
	}
	seq_printf(p, "intr %llu", (unsigned long long)sum);
	/* sum again ? it could be updated? */
	for_each_irq_nr(j)
		seq_put_decimal_ull(p, ' ', kstat_irqs_usr(j));
	seq_printf(p,
		"\nctxt %llu\n"
		"btime %lu\n"
		"processes %lu\n"
		"procs_running %lu\n"
		"procs_blocked %lu\n",
		nr_context_switches(),
		(unsigned long)jif,
		total_forks,
		nr_running(),
		nr_iowait());
	seq_printf(p, "softirq %llu", (unsigned long long)sum_softirq);
	for (i = 0; i < NR_SOFTIRQS; i++)
		seq_put_decimal_ull(p, ' ', per_softirq_sums[i]);
	seq_putc(p, '\n');
	return 0;
}
static int stat_open(struct inode *inode, struct file *file)
{
	size_t size = 1024 + 128 * num_possible_cpus();
	char *buf;
	struct seq_file *m;
	int res;
	/* minimum size to display an interrupt count : 2 bytes */
	size += 2 * nr_irqs;
	/* don't ask for more than the kmalloc() max size */
	if (size > KMALLOC_MAX_SIZE)
		size = KMALLOC_MAX_SIZE;
	buf = kmalloc(size, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;
	res = single_open(file, show_stat, NULL);
	if (!res) {
		m = file->private_data;
		m->buf = buf;
		m->size = ksize(buf);
	} else
		kfree(buf);
	return res;
}
static const struct file_operations proc_stat_operations = {
	.open		= stat_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= single_release,
};
static int __init proc_stat_init(void)
{
	proc_create("stat", 0, NULL, &proc_stat_operations);
	return 0;
}
fs_initcall(proc_stat_init);

參考

http://man7.org/linux/man-pages/man5/proc.5.html

https://github.com/pcolby/scripts/blob/master/cpu.sh

https://elixir.bootlin.com/linux/v3.14.69/source/fs/proc/stat.c

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