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Chapter 30. Creating and running containers

This section provides information about creating and running containers with the real-time kernel.

Prerequisites

  • Install podman and other container related utilities.
  • Get familiar with administration and management of Linux containers on RHEL.
  • Install the kernel-rt package and other real-time related packages.

30.1. Creating a container
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You can use all the following options with both the real time kernel and the main RHEL kernel. The kernel-rt package brings potential determinism improvements and allows the usual troubleshooting.

Prerequisites

  • You have administrator privileges.

Procedure

The following procedure describes how to configure the Linux containers in relation with the real time kernel.

  1. Create the directory you want to use for the container. For example: 

    # mkdir cyclictest
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  2. Change into that directory: 

    # cd cyclictest
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  3. Log into a host that provides a container registry service: 

    # podman login registry.redhat.io
Username: my_customer_portal_login
Password: ***
Login Succeeded!
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  4. Create a Containerfile: 

    # vim Dockerfile

FROM rhel8
RUN subscription-manager repos --enable=rhel-8-for-x86_64-rt-rpm
RUN dnf -y install rt-tests
ENTRYPOINT cyclictest --smp -p95
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  5. If you are building from a custom Containerfile modify your Containerfile and build it. Here is an example with cyclisttest. If not creating your own image, you can also pull the realtime-tests-container image to run cyclictest: 

    # podman build -t cyclictest .
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30.2. Running a container
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You can run a container built with a Containerfile.

Procedure

  1. Run a container using the podman run command: 

    # podman run --device=/dev/cpu_dma_latency --cap-add ipc_lock --cap-add sys_nice --cap-add sys_rawio --rm -ti cyclictest

/dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 0.08 0.10 0.09 2/947 15

T: 0 ( 8) P:95 I:1000 C: 3209 Min: 1 Act: 1 Avg: 1 Max:  14

T: 1 ( 9) P:95 I:1500 C: 2137 Min: 1 Act: 2 Avg: 1 Max:  23

T: 2 (10) P:95 I:2000 C: 1601 Min: 1 Act: 2 Avg: 2 Max:   7

T: 3 (11) P:95 I:2500 C: 1280 Min: 1 Act: 2 Avg: 2 Max:  72

T: 4 (12) P:95 I:3000 C: 1066 Min: 1 Act: 1 Avg: 1 Max:   7

T: 5 (13) P:95 I:3500 C:  913 Min: 1 Act: 2 Avg: 2 Max:  87

T: 6 (14) P:95 I:4000 C:  798 Min: 1 Act: 1 Avg: 2 Max:   7

T: 7 (15) P:95 I:4500 C:  709 Min: 1 Act: 2 Avg: 2 Max:  29
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This example shows the podman run command with the required, real time-specific options. For example:

  • The first in first out (FIFO) scheduler policy is made available for workloads running inside the container through the --cap-add=sys_nice option. This option also allows setting the CPU affinity of threads, another important configuration dimension when tuning a real time workload.

  • The --device=/dev/cpu_dma_latency option makes the host device available inside the container (subsequently used by the cyclictest workload to configure the CPU idle time management). If the specified device is not made available, an error similar to the message below appears:

    WARN: stat /dev/cpu_dma_latency failed: No such file or directory

    When confronted with error messages like these, refer to the podman-run(1) manual page. To get a specific workload running inside a container, other podman-run options may be helpful.

    In some cases, you also need to add the --device=/dev/cpu option to add that directory hierarchy, mapping per-CPU device files such as /dev/cpu/*/msr.

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