Running "top" command inside docker container

[sourav82]

Output of docker version:

Client:
 Version:      1.11.2
 API version:  1.23
 Go version:   go1.5.4
 Git commit:   b9f10c9
 Built:        Wed Jun  1 21:47:50 2016
 OS/Arch:      linux/amd64

Server:
 Version:      1.11.2
 API version:  1.23
 Go version:   go1.5.4
 Git commit:   b9f10c9
 Built:        Wed Jun  1 21:47:50 2016
 OS/Arch:      linux/amd64

Output of docker info:

Containers: 4
 Running: 2
 Paused: 0
 Stopped: 2
Images: 21
Server Version: 1.11.2
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 110
 Dirperm1 Supported: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins: 
 Volume: local
 Network: host bridge null
Kernel Version: 3.19.0-25-generic
Operating System: Ubuntu 14.04.4 LTS
OSType: linux
Architecture: x86_64
CPUs: 1
Total Memory: 1.946 GiB
Name: ubuntu
ID: GQA6:C24M:QCWL:XELO:3V5I:XSW7:7ONJ:SLW2:R64S:R6AI:AEN6:MCEP
Docker Root Dir: /var/lib/docker
Debug mode (client): false
Debug mode (server): false
Registry: https://index.docker.io/v1/
WARNING: No swap limit support

Steps to reproduce the issue:
1.

docker run -it ubuntu /bin/bash

1. Inside the container created in step 1, run "top"command

Describe the results you received:

top - 18:03:52 up 17:37,  0 users,  load average: 0.35, 0.25, 0.25
Tasks:   2 total,   1 running,   1 sleeping,   0 stopped,   0 zombie
%Cpu(s): 10.6 us,  5.6 sy,  0.0 ni, 83.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   2040836 total,  1905172 used,   135664 free,   126276 buffers
KiB Swap:   522236 total,       24 used,   522212 free.  1195708 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND       
    1 root      20   0   18180   3272   2784 S  0.0  0.2   0:00.21 bash          
   15 root      20   0   19880   2400   2044 R  0.0  0.1   0:00.80 top    

Describe the results you expected:

Compare %Cpu(s) in the 3rd line of output of "top"command and the total %CPU of each process inside the container. %Cpu(s) should be total %CPU used by each process (which is 0 in this case).

Additional information you deem important (e.g. issue happens only occasionally):

What is the %Cpu(s) count and how is it different from total %CPU used by each process inside the container?

[mYmNeo]

top read /proc/stat to show the %Cpu field, and it is not isolated and difficult to do by docker.

[sourav82]

Well, as I know container provides file system isolation as well. I could see /proc/stat inside container also. So, wondering how the namespaces are implemented in /proc file system. Any link in understanding it will be very helpful.