Linux CPU利用率计算原理及内核实现

来源：互联网发布：淘宝生e经的入口在哪里编辑：程序博客网时间：2024/06/18 13:46

我们经常使用top命令来查看CPU利用率，如

root@ubuntu:~# top

top – 09:16:29 up 6 min, 4 users, load average: 0.01, 0.22, 0.17

Tasks: 149 total, 1 running, 147 sleeping, 0 stopped, 1 zombie

Cpu(s): 2.8%us, 6.7%sy, 0.2%ni, 89.9%id, 0.3%wa, 0.0%hi, 0.1%si, 0.0%st

Mem: 508000k total, 404092k used, 103908k free, 47764k buffers

Swap: 522236k total, 0k used, 522236k free, 184992k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

1 root 20 0 3040 1812 1252 S 0.0 0.4 0:01.81 init

2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd

3 root 20 0 0 0 0 S 0.0 0.0 0:00.06 ksoftirqd/0

5 root 20 0 0 0 0 S 0.0 0.0 0:00.56 kworker/u:0

6 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0

Linux系统中计算CPU利用率是通过读取/proc/stat文件数据而计算得来。CPU利用率计算方法如下：

root@ubuntu:~# cat /proc/stat

cpu 711 56 2092 7010 104 0 20 0 0 0

cpu0 711 56 2092 7010 104 0 20 0 0 0

intr 31161 94 64 0 1 75 0 3 0 0 0 0 0 1423 0 0 382 2825 4798 0 226 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 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

ctxt 101085

btime 1307117390

processes 2078

procs_running 1

procs_blocked 0

softirq 32534 0 7796 151 143 4225 0 81 0 12 20126

root@ubuntu:~#

第一行cpu为总的信息，cpu0 … cpun为各个具体CPU信息
cpu 711 56 2092 7010 104 0 20 0 0 0

上面共有10个值（单位：jiffies），前面8个值分别为：
User time， 711 Nice time， 56

System time， 2092 Idle time，7010

Waiting time，104 Hard Irq time， 0

SoftIRQ time，20 Steal time，0

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

%us=(User time + Nice time)/CPU时间*100%

%sy=(System time + Hard Irq time +SoftIRQ time)/CPU时间*100%

%id=(Idle time)/CPU时间*100%

%ni=(Nice time)/CPU时间*100%

%wa=(Waiting time)/CPU时间*100%

%hi=(Hard Irq time)/CPU时间*100%

%si=(SoftIRQ time)/CPU时间*100%

%st=(Steal time)/CPU时间*100%

我们根据/proc/stat文件来分析Linux内核统计数据实现方式。

内核实现

下面以内核源码版本2.6.32-71.29.1.el6 x86_64为例，来介绍内核源码实现。

/proc/stat文件的创建由函数proc_stat_init（）实现，在文件fs/proc/stat.c中，在内核初始化时调用。./proc/stat文件相关函数时间均在stat.c文件中。

对/proc/stat文件的读写方法为proc_stat_operations。

00160:static const structfile_operations proc_stat_operations= {

00161: .open =stat_open,

00162: .read =seq_read,

00163: .llseek =seq_lseek,

00164: .release =single_release,

00165:};

打开文件函数stat_open（），函数首先申请大小为size的内存，来存放临时数据（也是我们看到的stat里的最终数据）。

00136:static int stat_open(structinode *inode,struct file*file)

00137:{

00138: unsignedsize =4096 *(1+ num_possible_cpus()/ 32);

00139: char *buf;

00140: structseq_file *m;

00141: intres;

00142:

00143: / * don’t ask for more than the kmalloc() max size, currently 128 KB */

00144: if(size > 128 *1024)

00145: size= 128 *1024;

00146: buf= kmalloc(size,GFP_KERNEL);

00147: if(! buf)

00148: return- ENOMEM;

00149:

00150: res= single_open(file,show_stat,NULL);

00151: if(! res) {

00152: m= file- >private_data;

00153: m- >buf =buf;

00154: m- >size =size;

00155: }else

00156: kfree(buf);

00157: returnres;

00158:} ? end stat_open ?

00159:

/proc/stat文件的数据由show_stat（）函数填充。注意43行for_each_possible_cpu(i)循环，
是计算所有CPU的数据，

如我们前面的示例看到的/proc/stat文件中第一行cpu值。

00025:static int show_stat(structseq_file *p,void *v)

00026:{

00027: inti,j;

00028: unsigned longjif;

00029: cputime64_tuser,nice,system,idle,iowait,irq,softirq,steal;

00030: cputime64_tguest;

00031: u64sum =0;

00032: u64sum_softirq =0;

00033: unsigned intper_softirq_sums[NR_SOFTIRQS]= {0};

00034: structtimespec boottime;

00035: unsigned intper_irq_sum;

00036:

00037: user= nice =system = idle = iowait=

00038: irq= softirq = steal =cputime64_zero;

00039: guest= cputime64_zero;

00040: getboottime(&boottime);

00041: jif= boottime.tv_sec;

00042:

00043: for_each_possible_cpu(i) {

00044: user= cputime64_add(user,kstat_cpu(i).cpustat.user);

00045: nice= cputime64_add(nice,kstat_cpu(i).cpustat.nice);

00046: system= cputime64_add(system,kstat_cpu(i).cpustat.system);

00047: idle= cputime64_add(idle,kstat_cpu(i).cpustat.idle);

00048: idle= cputime64_add(idle,arch_idle_time(i));

00049: iowait= cputime64_add(iowait,kstat_cpu(i).cpustat.iowait);

00050: irq= cputime64_add(irq,kstat_cpu(i).cpustat.irq);

00051: softirq= cputime64_add(softirq,kstat_cpu(i).cpustat.softirq);

00052: steal= cputime64_add(steal,kstat_cpu(i).cpustat.steal);

00053: guest= cputime64_add(guest,kstat_cpu(i).cpustat.guest);

00054: for_each_irq_nr(j) {

00055: sum+= kstat_irqs_cpu(j,i);

00056: }

计算总的CPU各个值user、nice、system、idle、iowait、irq、softirq、steal后，就分别计算各个CPU的使用情况（78~103行）。

00057: sum+= arch_irq_stat_cpu(i);

00058:

00059: for(j = 0;j < NR_SOFTIRQS;j++) {

00060: unsigned intsoftirq_stat =kstat_softirqs_cpu(j,i);

00061:

00062: per_softirq_sums[j]+= softirq_stat;

00063: sum_softirq+= softirq_stat;

00064: }

00065: }

00066: sum+= arch_irq_stat();

00067:

00068: seq_printf(p,“cpu %llu %llu %llu %llu %llu %llu %llu %llu %llu\n”,

00069: (unsigned long long)cputime64_to_clock_t(user),

00070: (unsigned long long)cputime64_to_clock_t(nice),

00071: (unsigned long long)cputime64_to_clock_t(system),

00072: (unsigned long long)cputime64_to_clock_t(idle),

00073: (unsigned long long)cputime64_to_clock_t(iowait),

00074: (unsigned long long)cputime64_to_clock_t(irq),

00075: (unsigned long long)cputime64_to_clock_t(softirq),

00076: (unsigned long long)cputime64_to_clock_t(steal),

00077: (unsigned long long)cputime64_to_clock_t(guest));

00078: for_each_online_cpu(i) {

00079:

00080: / * Copy values here to work around gcc- 2.95.3, gcc- 2.96 */

00081: user= kstat_cpu(i).cpustat.user;

00082: nice= kstat_cpu(i).cpustat.nice;

00083: system= kstat_cpu(i).cpustat.system;

00084: idle= kstat_cpu(i).cpustat.idle;

00085: idle= cputime64_add(idle,arch_idle_time(i));

00086: iowait= kstat_cpu(i).cpustat.iowait;

00087: irq= kstat_cpu(i).cpustat.irq;

00088: softirq= kstat_cpu(i).cpustat.softirq;

00089: steal= kstat_cpu(i).cpustat.steal;

00090: guest= kstat_cpu(i).cpustat.guest;

00091: seq_printf(p,

00092: “cpu%d %llu %llu %llu %llu %llu %llu %llu %llu %llu\n”,

00093: i,

00094: (unsigned long long)cputime64_to_clock_t(user),

00095: (unsigned long long)cputime64_to_clock_t(nice),

00096: (unsigned long long)cputime64_to_clock_t(system),

00097: (unsigned long long)cputime64_to_clock_t(idle),

00098: (unsigned long long)cputime64_to_clock_t(iowait),

00099: (unsigned long long)cputime64_to_clock_t(irq),

00100: (unsigned long long)cputime64_to_clock_t(softirq),

00101: (unsigned long long)cputime64_to_clock_t(steal),

00102: (unsigned long long)cputime64_to_clock_t(guest));

00103: }

00104: seq_printf(p,“intr %llu”, (unsigned long long)sum);

00105:

00106: / * sum again ? it could be updated? */

00107: for_each_irq_nr(j) {

00108: per_irq_sum= 0;

00109: for_each_possible_cpu(i)

00110: per_irq_sum+= kstat_irqs_cpu(j,i);

00111:

00112: seq_printf(p,” %u”, per_irq_sum);

00113: }

00114:

00115: seq_printf(p,

00116: “\nctxt %llu\n”

00117: “btime %lu\n”

00118: “processes %lu\n”

00119: “procs_running %lu\n”

00120: “procs_blocked %lu\n”,

00121: nr_context_switches(),

00122: (unsigned long)jif,

00123: total_forks,

00124: nr_running(),

00125: nr_iowait());

00126:

00127: seq_printf(p,“softirq %llu”, (unsigned long long)sum_softirq);

00128:

00129: for(i = 0;i < NR_SOFTIRQS;i++)

00130: seq_printf(p,” %u”, per_softirq_sums[i]);

00131: seq_printf(p,“\n”);

00132:

00133: return0;

00134:} ? end show_stat ?

00135:

104行计算所有CPU上中断次数，107~113行计算CPU上每个中断向量的中断次数。注意：/proc/stat文件中，将所有可能的NR_IRQS个中断向量计数都记录下来，但我们的机器上通过只是用少量的中断向量，这就是看到/proc/stat文件中，intr一行后面很多值为0的原因。

show_stat（）函数最后获取进程切换次数nctxt、内核启动的时间btime、所有创建的进程processes、正在运行进程的数量procs_running、阻塞的进程数量procs_blocked和所有io等待的进程数量。

最后我们解释一下user、nice、system、idle、iowait、irq、softirq、steal值的含义：

用户时间(User time)

表示CPU执行用户进程的时间，包括nices时间。通常期望用户空间CPU越高越好。

系统时间(System time)

表示CPU在内核运行时间，包括IRQ和softirq时间。系统CPU占用率高，表明系统某部分存在瓶颈。通常值越低越好。

等待时间(Waiting time)

CPI在等待I/O操作完成所花费的时间。系统部应该花费大量时间来等待I/O操作，否则就说明I/O存在瓶颈。

空闲时间(Idle time)

系统处于空闲期，等待进程运行。

Nice时间(Nice time)

系统调整进程优先级所花费的时间。

硬中断处理时间(Hard Irq time)

系统处理硬中断所花费的时间。

软中断处理时间(SoftIrq time)

系统处理软中断中断所花费的时间。

丢失时间(Steal time)

被强制等待（involuntary wait）虚拟CPU的时间，此时hypervisor在为另一个虚拟处理器服务。