CPU过高，思路和定位
1、先用top命令找出CPU占比最高的
top - 09:11:37 up 21 min, 3 users, load average: 0.54, 0.25, 0.16
Tasks: 94 total, 1 running, 93 sleeping, 0 stopped, 0 zombie
%Cpu(s): 3.0 us, 6.4 sy, 0.0 ni, 89.3 id, 0.0 wa, 0.0 hi, 1.3 si, 0.0 st
KiB Mem : 499428 total, 81452 free, 131984 used, 285992 buff/cache
KiB Swap: 1572860 total, 1572860 free, 0 used. 325184 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2485 root 20 0 2024360 25616 12256 S 8.6 5.1 0:08.54 java
2436 root 20 0 154608 5500 4132 S 1.3 1.1 0:01.50 sshd
580 root 20 0 376240 9256 6804 S 0.3 1.9 0:00.20 NetworkManager
1331 root 20 0 0 0 0 S 0.3 0.0 0:00.41 kworker/0:1
1 root 20 0 128036 6604 4144 S 0.0 1.3 0:01.48 systemd
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 0:00.08 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
6 root 20 0 0 0 0 S 0.0 0.0 0:00.01 kworker/u2:0
7 root rt 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root 20 0 0 0 0 S 0.0 0.0 0:00.53 rcu_sched
2、 ps -ef 或者jps进一步定位，得知是一个怎样的一个后台程序给我们惹事
[root@node3 ~]# jps -l
2516 sun.tools.jps.Jps
2485 com.wu.pratice.jvm.UnableCreateNewThreadDemo
1413 -- process information unavailable
7162 -- process information unavailable
[root@node3 ~]# ps -ef | grep java
root 2485 2440 8 09:09 pts/2 00:00:26 java com.wu.pratice.jvm.UnableCreateNewThreadDemo
root 2527 2495 0 09:14 pts/1 00:00:00 grep --color=auto java
3、定位到具体线程或代码
ps -mp 进程 -o THREAD,tid,time
- -m 显示所有的线程
- -p 指定进程id
- -o 该参数后是用户自定义格式
[root@node3 ~]# ps -mp 2485 -o THREAD,tid,time
USER %CPU PRI SCNT WCHAN USER SYSTEM TID TIME
root 8.5 - - - - - - 00:00:30
root 0.0 19 - futex_ - - 2485 00:00:00
root 8.3 19 - n_tty_ - - 2486 00:00:29
root 0.0 19 - futex_ - - 2487 00:00:00
root 0.0 19 - futex_ - - 2488 00:00:00
root 0.0 19 - futex_ - - 2489 00:00:00
root 0.0 19 - futex_ - - 2490 00:00:00
root 0.0 19 - futex_ - - 2491 00:00:00
root 0.0 19 - futex_ - - 2492 00:00:00
root 0.0 19 - futex_ - - 2493 00:00:00
root 0.0 19 - futex_ - - 2494 00:00:00
4、将需要的线程ID转换为16进制格式（英文小写格式）
printf “%x\n” 2486 【2486的16进制为9B6】
5、jstack 进程ID | grep tid(16进程线程ID小写英文) -A60
-A 显示多少行
[root@node3 ~]# jstack 2485 | grep 9b6 -A60
"main" #1 prio=5 os_prio=0 tid=0x00007f165004b800 nid=0x9b6 runnable [0x00007f16590c3000]
java.lang.Thread.State: RUNNABLE
at java.io.FileOutputStream.writeBytes(Native Method)
at java.io.FileOutputStream.write(FileOutputStream.java:326)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
- locked <0x00000000fac20580> (a java.io.BufferedOutputStream)
at java.io.PrintStream.write(PrintStream.java:482)
- locked <0x00000000fac18170> (a java.io.PrintStream)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291)
at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104)
- locked <0x00000000fac18128> (a java.io.OutputStreamWriter)
at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185)
at java.io.PrintStream.newLine(PrintStream.java:546)
- eliminated <0x00000000fac18170> (a java.io.PrintStream)
at java.io.PrintStream.println(PrintStream.java:807)
- locked <0x00000000fac18170> (a java.io.PrintStream)
at com.wu.pratice.jvm.UnableCreateNewThreadDemo.main(UnableCreateNewThreadDemo.java:24)
"VM Thread" os_prio=0 tid=0x00007f16500cb800 nid=0x9b7 runnable
"VM Periodic Task Thread" os_prio=0 tid=0x00007f165011a000 nid=0x9be waiting on condition
JNI global references: 5
