環境

$docker info
Containers: 3
 Running: 3
 Paused: 0
 Stopped: 0
Images: 3
Server Version: 17.12.1-ce
Storage Driver: devicemapper
 Pool Name: docker-docker--pool
 Pool Blocksize: 524.3kB
 Base Device Size: 10.74GB
 Backing Filesystem: ext4
 Udev Sync Supported: true
 Data Space Used: 639.1MB
 Data Space Total: 23.33GB
 Data Space Available: 22.69GB
 Metadata Space Used: 536.6kB
 Metadata Space Total: 25.17MB
 Metadata Space Available: 24.63MB
 Thin Pool Minimum Free Space: 2.333GB
 Deferred Removal Enabled: true
 Deferred Deletion Enabled: true
 Deferred Deleted Device Count: 0
 Library Version: 1.02.135-RHEL7 (2016-11-16)
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 9b55aab90508bd389d7654c4baf173a981477d55
runc version: 9f9c96235cc97674e935002fc3d78361b696a69e
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.85-38.58.amzn1.x86_64
Operating System: Amazon Linux AMI 2017.09
OSType: linux
Architecture: x86_64
CPUs: 1
Total Memory: 993.2MiB
Name: ip-172-31-11-19
ID: J7FY:XV4I:XVQE:STLY:AXXC:K4KJ:U64D:OZGB:GJQF:VO3A:LL5C:YLST
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

やってみた

以下で実施。

# docker exec で bash を起動
$docker exec -it 865052a7af6f bash

# dd コマンドを実行
$dd if=/dev/zero of=/dev/null &
[1] 96

# bash を終了
$exit

これでOK.
確認

# docker stats で高い値
$docker stats 865052a7af6f
CONTAINER ID        NAME                                                               CPU %               MEM USAGE / LIMIT     MEM %               NET I/O             BLOCK I/O           PIDS
865052a7af6f       ecs-console-sample-app-static-10-simple-app-fa82a99aa2d39edd7600   99.64%              6.668MiB / 256MiB     2.60%               1.67kB / 0B         7.24MB / 4.1kB      0

# dd プロセスの %CPU が99.2
$top
 - 01:46:21 up 35 days,  3:09,  2 users,  load average: 0.44, 0.13, 0.04
Tasks: 121 total,   3 running, 118 sleeping,   0 stopped,   0 zombie
Cpu(s): 32.9%us, 67.1%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   1017056k total,   704388k used,   312668k free,   259880k buffers
Swap:        0k total,        0k used,        0k free,   235320k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
19330 root      20   0  4264  700  620 R 99.2  0.1   0:34.16 dd

EC2(t2.micron。これは vCPU が1) を使っていたが CPUUtilization メトリクスについてはずっと100%となっていた。