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fadedbee
Asked: 2012-11-13 02:55:49 +0800 CST

0% CPU in top for all processes, but load average > 1

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On two different servers (with Ubuntu 12.04LTS AMD64) I have seen the following behaviour:

op - 10:50:05 up 305 days, 21:17,  1 user,  load average: 1.94, 2.52, 2.97
Tasks: 141 total,   2 running, 139 sleeping,   0 stopped,   0 zombie
Cpu(s): 41.5%us,  6.5%sy,  0.0%ni, 51.8%id,  0.0%wa,  0.2%hi,  0.1%si,  0.0%st
Mem:   8178432k total,  5753740k used,  2424692k free,   159480k buffers
Swap: 15625208k total,        0k used, 15625208k free,  4905292k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                               
    1 root      20   0 23928 2072 1216 S    0  0.0   0:56.42 init                                                                                  
    2 root      20   0     0    0    0 S    0  0.0   0:00.01 kthreadd                                                                              
    3 root      RT   0     0    0    0 S    0  0.0   0:01.23 migration/0                                                                           
    4 root      20   0     0    0    0 S    0  0.0   2:39.82 ksoftirqd/0                                                                           
    5 root      RT   0     0    0    0 S    0  0.0   0:00.00 watchdog/0                                                                            
    6 root      RT   0     0    0    0 S    0  0.0   0:02.99 migration/1                                                                           
    7 root      20   0     0    0    0 S    0  0.0   2:32.15 ksoftirqd/1                                                                           
    8 root      RT   0     0    0    0 S    0  0.0   0:00.00 watchdog/1                                                                            
    9 root      RT   0     0    0    0 S    0  0.0   0:11.67 migration/2                                                                           
   10 root      20   0     0    0    0 S    0  0.0  29:00.34 ksoftirqd/2

The server is working fine, but top shows all processes as using 0% CPU. A reboot fixed this on an earlier machine, but I haven't yet tried it on this one.

I have tried top several times, and so am sure that I haven't accidentally pressed '<' or '>' to sort by a different column. Sorting the process list by all of the available columns, stills shows 0% CPU for all displayed processes.

What is going on? If this a kernel bug?

Update: If I use top -p <PID> for a known, busy process, top still displays 0% CPU for that process.

Update2: My point is that ALL processes are reporting 0% CPU usage ALL of the time.

linux

2 Answers

  1. Have a look at this article. http://blog.scoutapp.com/articles/2009/07/31/understanding-load-averages

    Typically Load with little to no CPU usage indicates I/O to disk/network. Load isn't a bad thing, but keeping an eye on the trends of your 1,5, and 15 min metrics will help you triage a real issue vs. trends.

    Maybe check out what your disks are doing via 'iostat'.

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  2. Load isn't CPU usage. Load is "amount of runnable processes". Seeing a load of almost 2 with no CPU usage means that some processes are probably doing a lot of IO, or maybe even stuck. Check with PS whether you have processes in D state for instance.

    (I had a mailserver with load 2200 last week, its storage failed. Everything else worked normally though :))

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