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[RHCE7] RH134 Chapter 5 Managing Priority of Linux Processes 學習筆記

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此文章記錄學習 RHCE7 RH134 Chapter 5 Managing Priority of Linux Processes 留下的內容
5.1 Process Priority and "nice" Concepts ========================================

nice 值範圍 -20 ~ 19，沒指定預設就是 0，愈小表示 priority 愈高

root 可以調大 or 調小 nice value，但一般使用者只能調大

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# 加上參數 -l 可取得 nice value(NI)
[vagrant@server ~]$ ps -l
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1000 11502 11501  0  80   0 - 28845 wait   pts/0    00:00:00 bash
0 R  1000 11572 11502  0  80   0 - 34343 -      pts/0    00:00:00 ps

PR 20 = nice 0

 5.2 Using nice and renice to Influence Process Priority =======================================================

★★★★★★★★★ Very Important! ★★★★★★★★★ (start)

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# o format => 使用者自訂顯示欄位
$ ps axo pid,comm,nice --sort=-nice
 PID COMMAND          NI
   26 khugepaged       19
  476 alsactl          19
   25 ksmd              5
  537 rtkit-daemon      1
    1 systemd           0
......
   11 rcuos/0           0
   12 watchdog/0        -
......
29921 ps                0
  449 auditd           -4
  467 sedispatch       -4
  462 audispd          -8
 1583 pulseaudio      -11
    5 kworker/0:0H    -20
.......

★★★★★★★★★ Very Important! ★★★★★★★★★ (end)

啟動程式時指定 nice 值：

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# nice 示範
$ nice -n 10 top
$ ps -al
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1000 11626 11502  0  90  10 - 36537 poll_s pts/0    00:00:00 top
0 R  1000 11627 11604  0  80   0 - 34343 -      pts/1    00:00:00 ps

# renice 示範
$ renice -n 15 11604
11604 (process ID) old priority 0, new priority 15
$ ps -al
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1000 11626 11502  0  90  10 - 36537 poll_s pts/0    00:00:00 top
0 R  1000 11630 11604  0  95  15 - 34343 -      pts/1    00:00:00 ps

補充：Hash Algorithm 特性

  1. 計算的資料來源沒有長度限制

  2. 雜湊長度永遠固定

  3. 雜湊演算法為單向運算

  4. 不同的資料來源不會產出相同的雜湊值

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$ sha1sum /etc/passwd
524dab4b600e8d87cb7aa5b21e4d57f8996a4374  /etc/passwd

$ echo "1234" | sha1sum
1be168ff837f043bde17c0314341c84271047b31  -

Practice: Discovery Process Properties

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# 根據 cpu 的核心數，執行兩倍數量的運算工作
$ for i in $( seq $(($(grep -c '^processor' /proc/cpuinfo) * 2)) ); do sha1sum /dev/zero & done
[1] 31701
[2] 31702

$ jobs
[1]-  Running                 sha1sum /dev/zero &
[2]+  Running                 sha1sum /dev/zero &

# 使用參數 u 可檢視資源使用率
$ ps u $(pgrep sha1sum)
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
student  31701 50.0  0.0 116096  1044 pts/0    R    14:26   1:29 sha1sum /dev/zero
student  31702 50.0  0.0 116096  1044 pts/0    R    14:26   1:29 sha1sum /dev/zero

$ nice -n 10 sha1sum /dev/zero &
[3] 31764

# 透過參數 o 指定顯示欄位 (nice value = 10 的 process 所佔的資源相對低)
$ ps o pid,pcpu,nice,comm $(pgrep sha1sum)
  PID %CPU  NI COMMAND
31701 49.8   0 sha1sum
31702 49.8   0 sha1sum
31764  4.0  10 sha1sum

# 調整 process nice value，可看出資源使用率有提升
$ sudo renice -n 5 31764
$ ps o pid,pcpu,nice,comm $(pgrep sha1sum)
  PID %CPU  NI COMMAND
31701 48.8   0 sha1sum
31702 48.8   0 sha1sum
31764  6.2   5 sha1sum

# 移除所有使用 sha1sum 指令產生的 process
$ killall sha1sum
$ ps o pid,pcpu,nice,comm $(pgrep sha1sum)
  PID %CPU  NI COMMAND
 2052  0.0   0 bash
31825  0.0   0 ps
[1]   Terminated              sha1sum /dev/zero
[2]-  Terminated              sha1sum /dev/zero
[3]+  Terminated              nice -n 10 sha1sum /dev/zero