Linux进程优先级调整

1. Linux top命令输出中PR值和NI值有什么不同

NI 是优先值&＃xff0c;是用户层面的概念&＃xff0c; PR是进程的实际优先级&＃xff0c; 是给内核&＃xff08;kernel&＃xff09;看&＃xff08;用&＃xff09;的。

一般情况下&＃xff0c;PR&＃61;NI&＃43;20, 如果一个进程的优先级PR是20&＃xff0c; 那么它的NI(nice)值就是20-20&＃61;0。

可以通过改变NI来改变PR: PRI(new) &＃61; PRI(old) &＃43; nice



NI is the nice value, which is a user-space concept. PR is the process&＃39;s actual priority, as viewed by the Linux kernel.



For normal processes, the kernel priority is simply &＃43;20 from the nice value. Thus a process with the neutral nice value of zero has a kernel priority of 20. This offset-by-20 is done so that a process with a nice value of -20, the highest priority nice value, receives a kernel priority of zero. Lower numeric values equal higher scheduling priority.



For realtime processes, the kernel priority is the process&＃39;s real-time priority, but thePR column will simply print RT.



In some versions of the Linux kernel, the kernel priority could differ from the nice value, as the process scheduler applied a small bonus or punishment to interactive or processor-hogging tasks, respectively. In these older kernels, the value given by the PR column could differ from the nice value. This isn&＃39;t true with the kernel&＃39;s current scheduler, the Completely Fair Scheduler (CFS).

 

This article come from:

 http://www.quora.com/Linux/What-is-the-difference-between-the-NI-and-PR-values-in-the-top-1-commands-output

 

2. Nice调整限制:

nice 值可调整的范围为 -20 ~ 19 &＃xff1b;

Useful priorities are: 20 (the affected processes will run only when nothing else

     in the system wants to), 0 (the &＃39;&＃39;base&＃39;&＃39; scheduling priority), anything negative (to make things go very fast).

root 可随意调整自己或他人程序的 Nice 值&＃xff0c;且范围为 -20 ~ 19 &＃xff1b;

一般使用者仅可调整自己程序的 Nice 值&＃xff0c;且范围仅为 0 ~ 19 (避免一般用户抢占系统资源)&＃xff1b;

一般使用者仅可将 nice 值越调越高&＃xff0c;例如本来 nice 为 5 &＃xff0c;则未来仅能调整到大于 5&＃xff1b;



3. Nice调整方法

3.1新执行的指令即给予新的 nice 值

[root&＃64;www ~]# nice [-n 数字] command

选项与参数&＃xff1a;

-n  &＃xff1a;后面接一个数值&＃xff0c;数值的范围 -20 ~ 19。

  www.2cto.com  

用ps -l查的话&＃xff0c;里面显示的PRI就是PRI(new)&＃xff0c;核心会自动调整&＃xff0c;不是PRI(old) &＃43; nice的值&＃xff0c;会调高一点点



3.2 已存在程序的 nice 重新调整

        renice [number] PID

        

4. 设置某用户的所有进程优先级

修改/etc/security/limits.conf, 增加一行

userxxx - nice 19



要使 limits.conf 文件配置生效&＃xff0c;必须要确保 pam_limits.so 文件被加入到启动文件中。查看 /etc/pam.d/login 文件中有&＃xff1a;

session required /lib/security/pam_limits.so





5. 其他&＃xff1a;

5.1用taskset限制进程的CPU使用率:

http://www.cyberciti.biz/tips/setting-processor-affinity-certain-task-or-process.html

http://www.jb51.net/LINUXjishu/97275.html



5.2采用cpulimit限制进程的CPU使用率(发生SIGSTOP和SIGCONT信号):

http://cpulimit.sourceforge.net/

http://www.ttlsa.com/tools/cpulimit-limit-cpu-usage-on-linux/

http://maxmanii.blog.163.com/blog/static/1200622672009517112429702/