服务器cpu负载过高问题排查

第一步 ：执行top命令，查出当前机器线程情况

top - 09:14:36 up 146 days, 20:24,  1 user,  load average: 0.31, 0.37, 0.45
Tasks: 338 total,   1 running, 337 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.4%us,  0.4%sy,  0.0%ni, 99.2%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  16331456k total, 14017124k used,  2314332k free,   316724k buffers
Swap: 16506876k total,    36200k used, 16470676k free,  5151404k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                              
 6107 root      20   0 9724m 1.3g  15m S  8.0  8.4 624:22.34 java                                                                                                  
26678 root      20   0 9643m 498m  17m S  8.0  3.1  61:34.58 java                                                                                                  
10168 root      20   0 12.9g 4.7g  12m S  1.7 30.0 329:11.58 java                                                                                                  
11291 root      20   0 9654m 1.2g  15m S  0.7  7.7  35:17.04 java                                                                                                  
28662 root      20   0 15168 1436  940 R  0.7  0.0   0:00.12 top                                                                                                   
   61 root      20   0     0    0    0 S  0.3  0.0   4:10.55 ksoftirqd/14                                                                                          
   68 root      20   0     0    0    0 S  0.3  0.0 119:58.11 events/1                                                                                              
 2987 root      20   0     0    0    0 S  0.3  0.0  31:22.27 flush-253:2                                                                                           
    1 root      20   0 19344 1204  980 S  0.0  0.0   0:03.71 init             

第二步：通过jstack命令dump当前内存中线程信息
jstack 26678

[root@172_16_1_177 logs]# jstack 26678
2017-08-30 10:34:29
Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.79-b02 mixed mode):

"Attach Listener" daemon prio=10 tid=0x00007f96dc001000 nid=0x70d5 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"DubboServerHandler-172.16.1.177:28082-thread-50" daemon prio=10 tid=0x00007f967c001800 nid=0x70a1 waiting on condition [0x00007f9543040000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000000ca928680> (a java.util.concurrent.SynchronousQueue$TransferStack)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
    at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:458)
    at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:359)
    at java.util.concurrent.SynchronousQueue.take(SynchronousQueue.java:925)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

"DubboServerHandler-172.16.1.177:28082-thread-49" daemon prio=10 tid=0x00007f95f820c000 nid=0x708e waiting on condition [0x00007f9543081000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000000ca928680> (a java.util.concurrent.SynchronousQueue$TransferStack)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
    at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:458)
    at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:359)
    at java.util.concurrent.SynchronousQueue.take(SynchronousQueue.java:925)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

"DubboServerHandler-172.16.1.177:28082-thread-48" daemon prio=10 tid=0x00007f9674001800 nid=0x7085 waiting on condition [0x00007f95430c2000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000000ca928680> (a java.util.concurrent.SynchronousQueue$TransferStack)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
    at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:458)
    at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:359)
    at java.util.concurrent.SynchronousQueue.take(SynchronousQueue.java:925)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

"DubboServerHandler-172.16.1.177:28082-thread-47" daemon prio=10 tid=0x00007f95f820a000 nid=0x7084 waiting on condition [0x00007f9543103000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000000ca928680> (a java.util.concurrent.SynchronousQueue$TransferStack)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
    at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:458)
    at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:359)
    at java.util.concurrent.SynchronousQueue.take(SynchronousQueue.java:925)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

"DubboServerHandler-172.16.1.177:28082-thread-46" daemon prio=10 tid=0x00007f95f8207800 nid=0x7082 waiting on condition [0x00007f9543144000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000000ca928680> (a java.util.concurrent.SynchronousQueue$TransferStack)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
    at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:458)
    at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:359)
    at java.util.concurrent.SynchronousQueue.take(SynchronousQueue.java:925)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

4.1、使用方案
cpu飙高，load高，响应很慢
方案：
* 一个请求过程中多次dump
* 对比多次dump文件的runnable线程，如果执行的方法有比较大变化，说明比较正常。如果在执行同一个方法，就有一些问题了。
查找占用cpu最多的线程信息
方案：
* 使用命令： top -H -p pid（pid为被测系统的进程号），找到导致cpu高的线程id。
上述Top命令找到的线程id，对应着dump thread信息中线程的nid，只不过一个是十进制，一个是十六进制。
* 在thread dump中，根据top命令查找的线程id，查找对应的线程堆栈信息。
cpu使用率不高但是响应很慢
方案：
* 进行dump，查看是否有很多thread struck在了i/o、数据库等地方，定位瓶颈原因。
请求无法响应
方案：
* 多次dump，对比是否所有的runnable线程都一直在执行相同的方法，如果是的，恭喜你，锁住了！

参考资料：http://blog.csdn.net/rachel_luo/article/details/8920596