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Cgroup

Monitoring

Cgroup has a hierarchical structure, you can use systemctl status command to see the Cgroup tree. You can use systemd-cgtop to monitor the real-time resource usage of each Cgroup.

CPU Sub-system

Get the full ID of the container:

docker ps -q --no-trunc | grep cd5469264e5f

Cgroup directory location:

/sys/fs/cgroup/cpu/docker/cd5469264e5ffd983e532aabcaa8378e2a37f3c8d76d7fe4312c8783dca10bc7

Pin Container to Cores

Location:

/sys/fs/cgroup/cpuset/docker/cd5469264e5ffd983e532aabcaa8378e2a37f3c8d76d7fe4312c8783dca10bc7/cpuset.cpus

Disk I/O Rate Limiting

https://andrestc.com/post/cgroups-io/

Disk I/O limits can be set by using blkio.throttle.write_bps_device (for write) and blkio.throttle.read_bps_device (for read). This requires us to specify limits by device, so we must find out our device major and minor version:

$ cat /proc/partitions
major minor  #blocks  name

   8        0   10485760 sda
   8        1   10484719 sda1
   8       16      10240 sdb

Then we can limit the write bytes per second to 1048576 (1MB/s) on the sda device (8:0) for a docker contaier with id container_id:

$ echo "8:0 1048576" > /sys/fs/cgroup/blkio/docker/container_id/blkio.throttle.write_bps_device

Network Bandwidth Limiting

https://www.kernel.org/doc/Documentation/cgroup-v1/net_cls.txt

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/resource_management_guide/sec-net_cls

The Network classifier cgroup provides an interface to tag network packets with a class identifier (classid). The Traffic Controller (tc) can be used to assign different priorities to packets from different cgroups. Also, Netfilter (iptables) can use this tag to perform actions on such packets.

This net_cls.classid value is initialized to 0. You can write hexadecimal values to net_cls.classid; the format for these values is 0xAAAABBBB; AAAA is the major handle number and BBBB is the minor handle number. Reading net_cls.classid yields a decimal result.

Example:

echo 0x100001 >  /sys/fs/cgroup/net_cls/0/net_cls.classid
	- setting a 10:1 handle.
cat /sys/fs/cgroup/net_cls/0/net_cls.classid
1048577

Configuring tc:

tc qdisc add dev eth0 root handle 10: htb

tc class add dev eth0 parent 10: classid 10:1 htb rate 40mbit
 - creating traffic class 10:1