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mrme 02-24-2012 08:43 PM
CPU usage by processes using top command
 
Guys,

I'm new here so forgive my ignorance if I'm missing something here.

Wonder if someone can help me here, or point me to the right rtfm :-)


I'm using top command to determine total cpu utilization by applications. If you look at below top output, you can see CPU is 52.4% utilized.

i.e. 9.7 + 9.1 + 0.7 + 1.2 + 31.7 = 52.4% and including the idle (47.5 + 52.4 = 99.9%) would give you the total CPU - still not sure why 0.1 is missing ;)


Code:
  top - 20:39:33 up 28 min,  1 user,  load average: 12.38, 10.38, 6.31
Tasks: 311 total,  17 running, 294 sleeping,  0 stopped,  0 zombie
Cpu(s):  9.7%us,  9.1%sy,  0.0%ni, 47.5%id,  0.7%wa,  1.2%hi, 31.7%si,  0.0%st
Mem:  33012208k total,  3576120k used, 29436088k free,    31988k buffers
Swap:        0k total,        0k used,        0k free,  485704k cached
There are 8 CPUs/Cores so total CPU percentage would be 100x8 = 800%.

Now I have a custom script that's keeping the CPUs busy

Code:
PID  USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
44367 root      19  -1  2720  844  728 R 48.4  0.0  0:02.05 myscript
44365 root      19  -1  2720  848  728 R 46.9  0.0  0:02.35 myscript
44448 root      19  -1  2720  844  728 R 43.9  0.0  0:01.78 myscript
44665 root      19  -1  2720  844  728 R 43.9  0.0  0:00.96 myscript
44772 root      19  -1  2720  848  728 R 43.9  0.0  0:00.29 myscript
54460 mrme      19  -1 1587m  54m 2992 R 36.3  0.2  7:51.67 myscript
54462 mrme      19  -1 1586m  53m 2992 R 34.8  0.2  7:15.12 myscript
54463 mrme      19  -1 1587m  54m 2992 R 34.8  0.2  7:58.44 myscript
54461 mrme      19  -1 1586m  54m 2992 R 33.3  0.2  7:26.50 myscript
54464 mrme      19  -1 1587m  54m 2992 R 31.8  0.2  7:37.07 myscript
54465 mrme      19  -1 1587m  54m 2992 S 31.8  0.2  7:24.34 myscript
54466 mrme      19  -1 1587m  54m 2992 R 31.8  0.2  7:40.44 myscript
54459 mrme      19  -1 1588m  55m 3036 R 30.2  0.2  7:10.97 myscript
 3342 root      18  -2 34596  18m 1872 S 27.2  0.1  0:39.38 myscript
 4332 root      18  -2 40252  19m 1956 S 13.6  0.1  2:12.55 myscript
44760 root      20  0 19132 1300  824 R  7.6  0.0  0:00.13 top -c -b -n 1   
54458 root      19  -1 34184  19m 1560 S  6.0  0.1  0:45.39 monitor.pl     
  25 root      15  -5    0    0    0 S  3.0  0.0  0:06.60 [ksoftirqd/7]     
54455 root      19  -1 1599m  54m 2844 S  3.0  0.2  0:10.42 myscript
  16 root      15  -5    0    0    0 S  1.5  0.0  0:10.23 [ksoftirqd/4]     
 4716 root      19  -1  161m 101m  74m S  1.5  0.3  0:03.74 script2.sh
    1 root      20  0 10320  672  572 S  0.0  0.0  0:41.31 init [3]

If I sum up the CPU usage for all the processes (myscript) that would be:

48.4 + 46.9 + 43.9 + 43.9 + 43.9 + 36.3 + 34.8 + 34.8 + 33.3 + 31.8 + 31.8 + 31.8 + 30.2 + 27.2 + 13.6 + 7.6 + 6.0 + 3.0 + 3.0 + 1.5 + 1.5 = 555.2%

That means that the processes are using 555.2% of 800% CPU (correct me if I'm doing it wrong) In another words, it's 69.4% of the total CPU usage. But top's top shows that total CPU utilization is 52.4% why is there a difference of 17%? Which one should I trust, the total top calculated value or the total average processes usage? which one is accurate?

I'm not saying that the top is buggy, but I'm sure there's something I'm missing, whether it's the top refresh cycle or something else I need to know?


Would greatly appreciate your help.

syg00 02-24-2012 09:13 PM
Welcome to the vagaries of sampling monitors.

Let's start at the beginning - how (exactly) did you produce that top listing.

mrme 02-24-2012 09:52 PM
Actually this was taken from a production box, and the 'command' column had the actual long&ugly commands, so I had to just rename it 'myscript'.

The box is handling thousands of connections per second, 'myscript' is handling those connections (http),

the output is the result of 'top -c -b -n 1'


My point here is why does the total sum of the CPU usage of all the processes greater than the actual CPU utilization as shown in top header.


Thanks

syg00 02-24-2012 10:36 PM
I would suggest you (re-)read the manpage - particularly the bit in "BUGS". Then you will understand why I asked.


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