Load和CPU利用率是如何算出来的
Load和CPU利用率是如何算出来的
http://www.penglixun.com/tech/system/how_to_calc_load_cpu.html
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网址: http://www.penglixun.com/tech/system/how_to_calc_load_cpu.html
相信很多人都对Linux中top命令里“load average”这一栏困惑过，到底什么是Load，Load代表了什么含义，Load高会有什么后果？“%CPU”这一栏为什么会超过100%，它是如何计算的？
带着这些问题，我们通过一些测试，来探索下其中的不解之处。
首先，我们通过实验来大概确定其计算方式：
测试服务器：4核Xeon处理器
测试软件：MySQL 5.1.40
服务器上除了MySQL没有运行其他任何非系统自带软件。因为MySQL只能单线程运行单条SQL，所以可以很好的通过增加查询并发来控制使用的CPU核数。
空载时，top的信息为：
top – 14:51:47 up 35 days, 4:43, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 76 total, 1 running, 75 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 99.5%id, 0.1%wa, 0.2%hi, 0.2%si, 0.0%st
在数据库中启动一个大查询：
top – 15:28:09 up 35 days, 5:19, 3 users, load average: 0.99, 0.92, 0.67
Tasks: 80 total, 1 running, 79 sleeping, 0 stopped, 0 zombie
Cpu0 : 0.0%us, 0.0%sy, 0.0%ni, 96.3%id, 0.0%wa, 1.3%hi, 2.3%si, 0.0%st
Cpu1 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu2 : 98.7%us, 1.3%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu3 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
同时可以看到%CPU也是在100%
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
877 mysql 15 0 308m 137m 4644 S 99.9 6.8 15:13.28 mysqld
然后开启第二个大查询，不久就可以看到top信息的变化，Load到了2：
top – 15:36:44 up 35 days, 5:28, 3 users, load average: 1.99, 1.62, 1.08
Tasks: 80 total, 1 running, 79 sleeping, 0 stopped, 0 zombie
Cpu0 : 0.0%us, 0.0%sy, 0.0%ni, 97.7%id, 0.0%wa, 1.0%hi, 1.3%si, 0.0%st
Cpu1 : 99.0%us, 1.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu2 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu3 : 99.0%us, 1.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
也可以观察到%CPU增加到了200%：
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
877 mysql 15 0 312m 141m 4644 S 199.8 7.0 22:31.27 mysqld
由此可以简单的做出如下临时结论：
1. %CPU是由每个核的CPU占用律之和算出来的。
2. load跟执行的任务数有关
不过要想准确的知道其含义，还是必须从源码入手。
CPU利用率的计算方法
下载busybox的源码，在procps目录下有top.c的源码，查看第293行附近（1.17.1版），可以看到
这就是计算%CPU的代码，很明显total_pcpu就是累加了每个线程对每个核的使用率，所以%CPU的最大值就是核数*100%。
而CPU利用率又是怎么计算的呢，跟踪代码可以发现，是从系统的/proc/stat这里读取的，这个文件的格式可以参考：http://www.linuxhowtos.org/System/procstat.htm，下面是我笔记本上读出来的内容。
plx@plinux-Laptop:~/busybox-1.17.1$ cat /proc/stat
0 0 0 0 0 0 1
0 93 0 5 0 183 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 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
processes 6707
procs_running 2
procs_blocked 0
cpuN的含义从左到右分别是：user、system、nice、idle、iowait、irq、softirq，具体含义可以看文档。
在下面几行的含义是：
“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。
那么CPU利用率可以使用以下方法，先取两个采样点，然后计算其差值：
这是一段Bash代码采集利用率的，摘自网络：
&span style=&margin: 0 padding: 0 color: rgb(102, 102, 102);&&&em&#!/bin/sh&/em&&/span&
&span style=&margin: 0 padding: 0 color: rgb(102, 102, 102);&&&em&##echo user nice system idle iowait irq softirq&/em&&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&CPULOG_1&/span&=$&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&(&/strong&&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&cat&/strong&&/span& &span style=&margin: 0 padding: 0 font-weight:&&/&/span&proc&span style=&margin: 0 padding: 0 font-weight:&&/&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&stat&/strong&&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&grep&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'cpu '&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&awk&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'{print $2& &$3& &$4& &$5& &$6& &$7& &$8}'&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&)&/strong&&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&SYS_IDLE_1&/span&=$&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&(&/strong&&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&echo&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$CPULOG_1&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&awk&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'{print $4}'&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&)&/strong&&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&Total_1&/span&=$&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&(&/strong&&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&echo&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$CPULOG_1&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&awk&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'{print $1+$2+$3+$4+$5+$6+$7}'&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&)&/strong&&/span&
&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&sleep&/strong&&/span& &span style=&margin: 0 padding: 0&&5&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&CPULOG_2&/span&=$&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&(&/strong&&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&cat&/strong&&/span& &span style=&margin: 0 padding: 0 font-weight:&&/&/span&proc&span style=&margin: 0 padding: 0 font-weight:&&/&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&stat&/strong&&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&grep&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'cpu '&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&awk&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'{print $2& &$3& &$4& &$5& &$6& &$7& &$8}'&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&)&/strong&&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&SYS_IDLE_2&/span&=$&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&(&/strong&&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&echo&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$CPULOG_2&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&awk&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'{print $4}'&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&)&/strong&&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&Total_2&/span&=$&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&(&/strong&&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&echo&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$CPULOG_2&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span& &span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&awk&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&'{print $1+$2+$3+$4+$5+$6+$7}'&/span&&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&)&/strong&&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&SYS_IDLE&/span&=&span style=&margin: 0 padding: 0 font-weight:&&`&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&expr&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$SYS_IDLE_2&/span& - &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$SYS_IDLE_1&/span&&span style=&margin: 0 padding: 0 font-weight:&&`&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&Total&/span&=&span style=&margin: 0 padding: 0 font-weight:&&`&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&expr&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$Total_2&/span& - &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$Total_1&/span&&span style=&margin: 0 padding: 0 font-weight:&&`&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&SYS_USAGE&/span&=&span style=&margin: 0 padding: 0 font-weight:&&`&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&expr&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$SYS_IDLE&/span&&span style=&margin: 0 padding: 0 font-weight:&&/&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$Total&/span&&span style=&margin: 0 padding: 0 font-weight:&&*&/span&&span style=&margin: 0 padding: 0&&100&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&bc&/strong&&/span& -l&span style=&margin: 0 padding: 0 font-weight:&&`&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&SYS_Rate&/span&=&span style=&margin: 0 padding: 0 font-weight:&&`&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&expr&/strong&&/span& &span style=&margin: 0 padding: 0&&100&/span&-&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$SYS_USAGE&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&bc&/strong&&/span& -l&span style=&margin: 0 padding: 0 font-weight:&&`&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&Disp_SYS_Rate&/span&=&span style=&margin: 0 padding: 0 font-weight:&&`&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&expr&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&scale=3; &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$SYS_Rate&/span&/1&&/span& &span style=&margin: 0 padding: 0 font-weight:&&|&/span&&span style=&margin: 0 padding: 0 color: rgb(194, 12, 185);&&&strong&bc&/strong&&/span&&span style=&margin: 0 padding: 0 font-weight:&&`&/span&
&span style=&margin: 0 padding: 0 color: rgb(122, 8, 116);&&&strong&echo&/strong&&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 120, 0);&&$Disp_SYS_Rate&/span&&span style=&margin: 0 padding: 0 font-weight:&&%&/span&
还有一段Perl的代码，也是摘自网络：
&span style=&margin: 0 padding: 0 color: rgb(102, 102, 102);&&&em&#!/usr/bin/perl&/em&&/span&
&span style=&margin: 0 padding: 0 font-weight:&&use&/span& warnings&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SLEEPTIME&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&5&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(177, 177, 0);&&if&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&-&/span&e &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&/tmp/stat&&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&{&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/unlink.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&unlink&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&/tmp/stat&&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&}&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/open.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&open&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&JIFF_TMP&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&,&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&&&/tmp/stat&&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&||&/span& &a target=_blank href=&http://perldoc.perl.org/functions/die.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&die&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&Can't open /proc/stat file!&span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\n&/strong&&/span&&&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/open.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&open&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&JIFF&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&,&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&/proc/stat&&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&||&/span& &a target=_blank href=&http://perldoc.perl.org/functions/die.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&die&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&Can't open /proc/stat file!&span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\n&/strong&&/span&&&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@jiff_0&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/print.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&print&/span&&/a& JIFF_TMP &span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$jiff_0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/close.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&close&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&JIFF&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/sleep.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&sleep&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SLEEPTIME&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/open.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&open&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&JIFF&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&,&/span& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&/proc/stat&&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&||&/span& &a target=_blank href=&http://perldoc.perl.org/functions/die.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&die&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&Can't open /proc/stat file!&span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\n&/strong&&/span&&&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@jiff_1&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/print.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&print&/span&&/a& JIFF_TMP &span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$jiff_1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/close.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&close&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&JIFF&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/close.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&close&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&JIFF_TMP&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@USER&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&2}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@NICE&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&3}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@SYSTEM&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&4}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&5}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@IOWAIT&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&6}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@IRQ&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&7}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&@SOFTIRQ&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&`awk '{print &span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\$&/strong&&/span&8}' &/tmp/stat&`&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$JIFF_0&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$USER&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$NICE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SYSTEM&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IOWAIT&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IRQ&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SOFTIRQ&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$JIFF_1&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$USER&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$NICE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SYSTEM&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IOWAIT&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IRQ&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&+&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SOFTIRQ&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SYS_IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&0&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&-&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&[&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&]&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&/&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$JIFF_0&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&-&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$JIFF_1&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&*&/span& &span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&100&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SYS_USAGE&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&=&/span&&span style=&margin: 0 padding: 0 color: rgb(204, 102, 204);&&100&/span& &span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&-&/span& &span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SYS_IDLE&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
&a target=_blank href=&http://perldoc.perl.org/functions/printf.html& style=&color: rgb(34, 85, 136); text-decoration: margin: 0 padding: 0&&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 102);&&printf&/span&&/a& &span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&(&/span&&span style=&margin: 0 padding: 0 color: rgb(255, 0, 0);&&&The CPU usage is %1.2f%%&span style=&margin: 0 padding: 0 color: rgb(0, 0, 153);&&&strong&\n&/strong&&/span&&&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&,&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 0, 255);&&$SYS_USAGE&/span&&span style=&margin: 0 padding: 0 color: rgb(0, 153, 0);&&)&/span&&span style=&margin: 0 padding: 0 color: rgb(51, 153, 51);&&;&/span&
Load的计算方法
跟踪busybox的代码可以知道，load是从/proc/loadavg中读取的。
我本机的一次抓取内容如下：
plx@plinux-Laptop:~/busybox-1.17.1$ cat /proc/loadavg
0.64 0.81 0.86 3/364 6930
每个值的含义依次为：
lavg_1 (0.64) 1-分钟平均负载
lavg_5 (0.81) 5-分钟平均负载
lavg_15(0.86) 15-分钟平均负载
nr_running (3) 在采样时刻，运行队列的任务的数目，与/proc/stat的procs_running表示相同意思
nr_threads (364) 在采样时刻，系统中活跃的任务的个数（不包括运行已经结束的任务）
last_pid(6930) 最大的pid值，包括轻量级进程，即线程。
假设当前有两个CPU，则每个CPU的当前任务数为0.64/2=0.32
我们可以在Linux内核中找到loadavg文件的源码：
以及计算load的代码：
看了，理解了这些代码。
所以可以明白：Linux的系统负载指运行队列的平均长度，也就是等待CPU的平均进程数。&Linux的系统负载指运行队列的平均长度，也就是等待CPU的平均进程数。因为Linux内禁止浮点运算，因此系统的负载只能通过计算变化的次数这一修正值来计算。Linux内核定义一个长度为3的双字数组avenrun，双字的低11位用于存放负载的小数部分，高21位用于存放整数部分。当进程所耗的 CPU时间片数超过CPU在5秒内能够提供的时间片数时，内核计算上述的三个负载。负载初始化为0，假设最近1、5、15分钟内的平均负载分别为
load1、load5和load15，那么下一个计算时刻到来时，内核通过下面的算式计算负载：
load1 -= load1 -* exp(-5 / 60) -+ n * (1 – exp(-5 / 60 ))
load5 -= load5 -* exp(-5 / 300) + n * (1 – exp(-5 / 300))
load15 = load15 * exp(-5 / 900) + n * (1 – exp(-5 / 900))
其中，exp(x)为e的x次幂，n为当前运行队列的长度。Linux内核认为进程的生存时间服从参数为1的指数分布，指数分布的概率密度为：以内核计算负载load1为例，设相邻两个计算时刻之间系统活动的进程集合为S0。从1分钟前到当前计算时刻这段时间里面活动的load1个进程，设他们的集合是 S1，内核认为的概率密度是:λe-λx，而在当前时刻活动的n个进程，设他们的集合是Sn内核认为的概率密度是1-λe-λx。其中x = 5 / 60，因为相邻两个计算时刻之间进程所耗的CPU时间为5秒，而考虑的时间段是1分钟(60秒)。那么可以求出最近1分钟系统运行队列的长度：
load1 = |S1| -* λe-λx + |Sn| * (1-λe-λx) = load1 * λe-λx + n * (1-λe-λx)
其中λ = 1， x = 5 / 60， |S1|和|Sn|是集合元素的个数，这就是Linux内核源文件shed.c的函数calc_load()计算负载的数学依据。
所以“Load值=CPU核数”，这是最理想的状态，没有任何竞争，一个任务分配一个核。
由于数据是每隔5秒钟检查一次活跃的进程数，然后根据这个数值算出来的。如果这个数除以CPU的核数，结果高于5的时候就表明系统在超负荷运转了。
没有更多推荐了，}