现象
分别使用 top 及 ps 查看 nginx（PID 为19910）进程的优先级。
1，top 中值为 20
top -b -n 1 -p 19910
top - 09:57:13 up 435 days, 19 min, 2 users, load average: 0.00, 0.00, 0.00
Tasks: 1 total, 0 running, 1 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem: 8175360 total, 4617480 used, 3557880 free, 167444 buffers
KiB Swap: 8384508 total, 10408 used, 8374100 free. 3955108 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
19910 root 20 0 85948 2944 1784 S 0.0 0.0 0:00.00 nginx
2，ps -eo pri 中值为 19
ps -eo pid,ppid,ni,pri,psr,pcpu,stat,cmd |head -n1;ps -eo pid,ppid,ni,pri,psr,pcpu,stat,cmd |grep nginx
PID PPID NI PRI PSR %CPU STAT CMD
19910 1 0 19 0 0.0 Ss nginx: master process /usr/sbin/nginx
19911 19910 0 19 2 0.0 S nginx: worker process
19912 19910 0 19 1 0.0 S nginx: worker process
19914 19910 0 19 1 0.0 S nginx: worker process
19915 19910 0 19 0 0.0 S nginx: worker process
3，ps -elf 中值为 80
ps -elf |head -n1;ps -elf |grep [n]ginx
F S UID PID PPID C PRI NI ADDR SZ WCHAN STIME TTY TIME CMD
5 S root 19910 1 0 80 0 - 34452 sigsus Jul29 ? 00:00:00 nginx: master process /usr/sbin/nginx
5 S www-data 25732 19910 0 80 0 - 34485 ep_pol Aug31 ? 00:00:22 nginx: worker process
5 S www-data 25733 19910 0 80 0 - 34555 ep_pol Aug31 ? 00:00:23 nginx: worker process
5 S www-data 25734 19910 0 80 0 - 34452 ep_pol Aug31 ? 00:00:24 nginx: worker process
5 S www-data 25735 19910 0 80 0 - 34452 ep_pol Aug31 ? 00:00:23 nginx: worker process
ps 中的 priority
ps 中的 priority 共有如下几种，其中 priority 为原始值，其值为 /proc/[pid]/stat 中的第 18 列，其他值均由其计算而来。值越小，优先级越高。
| option | calculation | rt range | nrt range | notes |
|---|---|---|---|---|
| pri | 39-priority | 41 to 139 | 0 to 39 | |
| priority | priority | -100 to -2 | -39 to 0 | raw value |
| opri | 60+priority | -40 to 58 | 60 to 99 | |
| pri_api | -1 - priority | 1 to 99 | -40 to -1 | correct for RT |
| pri_bar | priority + 1 | -99 to -1 | 1 to 40 | |
| pri_baz | priority + 100 | 1 to 99 | 100 to 139 | internal kernel priority |
| pri_foo | priority-20 | -120 to -21 | -20 to 19 | correct for NRT |
-
Real-time Tasks
- 实时任务是有时间限制的任务，有期限，必须在期限前完成。
- 无 nice 值。
- 任务的调度优先级永远高于所有的非实时任务。
-
Non-Real-time Tasks
- 非实时任务是无时间限制的任务，无期限，无需在期限前完成。
- 有 nice 值。
- 现代计算机系统中已不再使用。
使用以下 ps 命令可将 nginx 进程的各个 priority 的值打印出来。
ps -o pid,nice,pri,priority,opri,pri_api,pri_bar,pri_baz,pri_foo 19910
PID NI PRI PRI PRI API BAR BAZ FOO
19910 0 19 20 80 -21 21 120 0
分析
- top
top 打印的值为原始值 priority，为 20，可使用以下命令获取到：
awk '{print $18}' /proc/19910/stat
20
// legal as UNIX "PRI"
// "priority" (was -20..20, now -100..39)
static int pr_priority(char *restrict const outbuf, const proc_t *restrict const pp){ /* -20..20 */
return snprintf(outbuf, COLWID, "%ld", pp->priority);
}
- ps -eo pri
pri 值为 39 减去 priority。
pri = 39 - priority = 39 - 20 = 19
// not legal as UNIX "PRI"
// "pri" (was 20..60, now 0..139)
static int pr_pri(char *restrict const outbuf, const proc_t *restrict const pp){ /* 20..60 */
return snprintf(outbuf, COLWID, "%ld", 39 - pp->priority);
ps -elf
-l 选项默认取的是 opri 的值，其值为 priority 的值加上 60。
opri = priority + 60 = 20 + 60 = 80
// legal as UNIX "PRI"
// "intpri" and "opri" (was 39..79, now -40..99)
static int pr_opri(char *restrict const outbuf, const proc_t *restrict const pp){ /* 39..79 */
return snprintf(outbuf, COLWID, "%ld", 60 + pp->priority);
}
REF
Commands ‘top’ and ‘ps’ show different values for priority - why?
ps priority(‘pri) different from value shown by top