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I am running a multithreaded program on my 8-core processor. top command shows 8 processes are running and each one utilizes a core by 100%. The problem is that only 21% are marked as user cpu and my application is running so slow:

Cpu(s): 20.6%us, 79.4%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

How can I find further information about the system processes those which have taken 79% of the CPU time? Specifically, I want to know what are these system calls.

Thanks in advance!

EDIT: This is what top returns:

top - 11:23:04 up 83 days,  1:20, 10 users,  load average: 8.00, 8.00, 8.00
Tasks: 267 total,  10 running, 257 sleeping,   0 stopped,   0 zombie
Cpu(s): 40.6%us, 17.4%sy,  0.0%ni, 41.9%id,  0.0%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:  16324640k total,  5645008k used, 10679632k free,   285368k buffers
Swap:  2047992k total,    32064k used,  2015928k free,  4584140k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                         
27262 ahmad     20   0  308m  32m  18m R 102.2  0.2   5022:32 Espresso                                                       
26872 ahmad     20   0  176m  12m 4540 R 100.0  0.1   5087:05 Espresso                                                       
27263 ahmad     20   0  175m  13m 4824 R 100.0  0.1   5022:35 Espresso                                                       
27265 ahmad     20   0  175m  12m 4508 R 100.0  0.1   5022:35 Espresso                                                       
26869 ahmad     20   0  308m  31m  18m R 98.3  0.2   5086:20 Espresso                                                        
26870 ahmad     20   0  175m  13m 4864 R 98.3  0.1   5087:05 Espresso                                                        
26871 ahmad     20   0  176m  12m 4592 R 98.3  0.1   5086:58 Espresso                                                        
27264 ahmad     20   0  176m  12m 4552 R 98.3  0.1   5022:06 Espresso                                                        
    1 root      20   0 19404 1164  940 S  0.0  0.0   0:02.12 init                                                            
    2 root      20   0     0    0    0 S  0.0  0.0   0:02.81 kthreadd      
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2 Answers 2

up vote 4 down vote accepted

It's time spent executing kernel code, but this does not mean that it has been triggered by system calls. For instance, it could be time spent reading large directories, but it could also be time spent handling iptables rules, or something else.

You can install the relevant package (it could be named linux-tools-2.6, but it depends on your distribution) and use perf top to look at what code the kernel is running. Read more here about perf.

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Fantastic! Just what I wanted! Thanks a lot :) –  ahmad Nov 13 '12 at 9:59

First of all. man top Here are some examples

CPU utilization from highest to lowest or vice versa SHIFT+r

MEM usage SHIFT+m

k = kill a process by it's pid

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