获取linux系统CPU使用率

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linux中监视系统运行信息，需要研究/proc下的一些信息，/proc/stat/给出了cpu的运行信息，先来分析一下

[work@builder ~]$ cat /proc/stat
cpu 432661 13295 86656 422145968 171474 233 5346
cpu0 123075 2462 23494 105543694 16586 0 4615
cpu1 111917 4124 23858 105503820 69697 123 371
cpu2 103164 3554 21530 105521167 64032 106 334
cpu3 94504 3153 17772 105577285 21158 4 24
intr 1065711094 1057275779 92 0 6 6 0 4 0 3527 0 0 0 70 0 20 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7376958 0 0 0 0 0 0 0 1054602 0 0 0 0 0 0 0 30 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ctxt 19067887
btime 1139187531
processes 270014
procs_running 1
procs_blocked 0

输出解释
CPU 以及CPU0、CPU1、CPU2、CPU3每行的每个参数意思（以第一行为例）为：
参数解释
user (432661) 从系统启动开始累计到当前时刻，用户态的CPU时间（单位：jiffies），不包含 nice值为负进程。1jiffies=0.01秒
nice (13295) 从系统启动开始累计到当前时刻，nice值为负的进程所占用的CPU时间（单位：jiffies）
system (86656) 从系统启动开始累计到当前时刻，核心时间（单位：jiffies）
idle (422145968) 从系统启动开始累计到当前时刻，除硬盘IO等待时间以外其它等待时间（单位：jiffies）
iowait (171474) 从系统启动开始累计到当前时刻，硬盘IO等待时间（单位：jiffies），
irq (233) 从系统启动开始累计到当前时刻，硬中断时间（单位：jiffies）
softirq (5346) 从系统启动开始累计到当前时刻，软中断时间（单位：jiffies）

CPU时间=user+system+nice+idle+iowait+irq+softirq

“intr”这行给出中断的信息，第一个为自系统启动以来，发生的所有的中断的次数；然后每个数对应一个特定的中断自系统启动以来所发生的次数。
“ctxt”给出了自系统启动以来CPU发生的上下文交换的次数。
“btime”给出了从系统启动到现在为止的时间，单位为秒。
“processes (total_forks) 自系统启动以来所创建的任务的个数目。
“procs_running”：当前运行队列的任务的数目。
“procs_blocked”：当前被阻塞的任务的数目。

通过两次读取/proc/stat文件，计算出cpu的busy和idle时间差。

代码只是简单的获取出CPU使用率，如果用到系统里，还是要用线程的。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdarg.h>
#include <errno.h>

#define STATES_line2x4 "%s\03" \
" %#5.1f%% \02user,\03 %#5.1f%% \02system,\03 %#5.1f%% \02nice,\03 %#5.1f%% \02idle\03\n"
static const char *States_fmts = STATES_line2x4;

//Total number of CPU
static int Cpu_tot;
// These typedefs attempt to ensure consistent 'ticks' handling
typedef unsigned long long TIC_t;

// This structure stores a frame's cpu tics used in history
// calculations.  It exists primarily for SMP support but serves
// all environments.
typedef struct CPU_t {
   TIC_t u, n, s, i, w, x, y;                             // as represented in /proc/stat
   TIC_t u_sav, s_sav, n_sav, i_sav, w_sav, x_sav, y_sav; // in the order of our display
   unsigned id;  // the CPU ID number
} CPU_t;

// This routine simply formats whatever the caller wants and
// returns a pointer to the resulting 'const char' string...
static const char *fmtmk (const char *fmts, ...)
{
static char buf[2048]; // with help stuff, our buffer
va_list va; // requirements exceed 1k

   va_start(va, fmts);
   vsnprintf(buf, sizeof(buf), fmts, va);
   va_end(va);
   return (const char *)buf;
}

static CPU_t *cpus_refresh (CPU_t *cpus)
{
   static FILE *fp = NULL;
   int i;
   int num;
   // enough for a /proc/stat CPU line (not the intr line)
   char buf[256+64];

   if (!fp) {
      if (!(fp = fopen("/proc/stat", "r")))
         printf("Failed /proc/stat open: %s", strerror(errno));

      //cpus = calloc(1, (1 + Cpu_tot) * sizeof(CPU_t));
      cpus = (CPU_t *)malloc((1 + Cpu_tot) * sizeof(CPU_t));
      memset(cpus, '\0', (1 + Cpu_tot) * sizeof(CPU_t));
   }
   rewind(fp);
   fflush(fp);

   // first value the last slot with the cpu summary line
   if (!fgets(buf, sizeof(buf), fp)) printf("failed /proc/stat read\n");
   cpus[Cpu_tot].x = 0;  // FIXME: can't tell by kernel version number
   cpus[Cpu_tot].y = 0;  // FIXME: can't tell by kernel version number
   num = sscanf(buf, "cpu %Lu %Lu %Lu %Lu %Lu %Lu %Lu",
      &cpus[Cpu_tot].u,
      &cpus[Cpu_tot].n,
      &cpus[Cpu_tot].s,
      &cpus[Cpu_tot].i,
      &cpus[Cpu_tot].w,
      &cpus[Cpu_tot].x,
      &cpus[Cpu_tot].y
   );
   if (num < 4)
         printf("failed /proc/stat read\n");

   // and just in case we're 2.2.xx compiled without SMP support...
   if (Cpu_tot == 1) {
      cpus[1].id = 0;
      memcpy(cpus, &cpus[1], sizeof(CPU_t));
   }
   // now value each separate cpu's tics
   for (i = 0; 1 < Cpu_tot && i < Cpu_tot; i++) {
      if (!fgets(buf, sizeof(buf), fp)) printf("failed /proc/stat read\n");
      cpus[i].x = 0;  // FIXME: can't tell by kernel version number
      cpus[i].y = 0;  // FIXME: can't tell by kernel version number
      num = sscanf(buf, "cpu%u %Lu %Lu %Lu %Lu %Lu %Lu %Lu",
         &cpus[i].id,
         &cpus[i].u, &cpus[i].n, &cpus[i].s, &cpus[i].i, &cpus[i].w, &cpus[i].x, &cpus[i].y
      );
      if (num < 4)
            printf("failed /proc/stat read\n");
   }
   return cpus;
}

static void summaryhlp (CPU_t *cpu, const char *pfx)
{
   // we'll trim to zero if we get negative time ticks,
   // which has happened with some SMP kernels (pre-2.4?)
#define TRIMz(x)  ((tz = (long long)(x)) < 0 ? 0 : tz)
   long long u_frme, s_frme, n_frme, i_frme, w_frme, x_frme, y_frme, tot_frme, tz;
   float scale;
if(cpu == NULL){
  printf("NULL@\n");
  return;
}
printf("u = %Lu, u_sav = %Lu\n", cpu->u, cpu->u_sav);

   u_frme = cpu->u - cpu->u_sav;
   s_frme = cpu->s - cpu->s_sav;
   n_frme = cpu->n - cpu->n_sav;
   i_frme = TRIMz(cpu->i - cpu->i_sav);
   w_frme = cpu->w - cpu->w_sav;
   x_frme = cpu->x - cpu->x_sav;
   y_frme = cpu->y - cpu->y_sav;
   tot_frme = u_frme + s_frme + n_frme + i_frme + w_frme + x_frme + y_frme;
   if (tot_frme < 1) tot_frme = 1;
   scale = 100.0 / (float)tot_frme;

    printf("scale = %0.5f\n", scale);
   // display some kinda' cpu state percentages
   // (who or what is explained by the passed prefix)
   printf(States_fmts,
         pfx,
         (float)u_frme * scale,
         (float)s_frme * scale,
         (float)n_frme * scale,
         (float)i_frme * scale,
         (float)w_frme * scale,
         (float)x_frme * scale,
         (float)y_frme * scale
       );
   // remember for next time around
   cpu->u_sav = cpu->u;
   cpu->s_sav = cpu->s;
   cpu->n_sav = cpu->n;
   cpu->i_sav = cpu->i;
   cpu->w_sav = cpu->w;
   cpu->x_sav = cpu->x;
   cpu->y_sav = cpu->y;

#undef TRIMz
}

int main()
{

static CPU_t * smpcpu = NULL;
for(;;){
Cpu_tot = sysconf(_SC_NPROCESSORS_ONLN);
printf("CPU number: %ld\n", Cpu_tot);
smpcpu = cpus_refresh(smpcpu);
summaryhlp(&smpcpu[Cpu_tot], "Cpu(s):");
printf("\n");
sleep(3);
smpcpu = cpus_refresh(smpcpu);
summaryhlp(&smpcpu[Cpu_tot], "Cpu(s):");
printf("++++++++++++++++++++++++++\n");
}
return 0;
}

转自：http://blog.163.com/sxs_solo/blog/static/2633338201011129811606/