In 3mdeb we use Docker heavily. Main tasks that we perform using it are:

• firmware and embedded software building - each software in Embedded System requires little bit different building environment, configuring those development environments on your host may quickly make a mess in your system for daily use, because of that we created various containers which I enumerate below
• trainings/workshops - when we perform trainings we don’t want to waste time for users to reconfigure the environment. In general, we have 2 choices: VM or containers. Since we use containers for building and development we prefer containers or containers in VMs while performing trainings.
• rootfs building for infrastructure deployment - we maintain pxe-server project which helps us in firmware testing and development. In that project we have a need for custom rootfs and kernels, we decided to combine Docker and Ansible for a reliable building of that infrastructure

To list some of our repositories:

• yocto-docker - container for building Yocto
• edk2-docker - container for building edk2 UEFI specification open source implementation
• xen-docker - container for building Xen hypervisor
• debian-rootfs-builder - container for building Debian rootfs and Linux kernels
• armbian-docker - docker for building Armbian Debian distribution for various ARM platforms
• zephyr-docker - container for building Zephyr RTOS
• esp-open-sdk-docker - container for bulding ESP Open SDK Espressify Open RTOS
• docker-mbed-cli - container for building and running CLI of mbedOS
• arch-pkg-builder - container for building Arch packages

Some are actively maintained, some are not, some came from other projects, some were created from scratch, but all of them have value for Embedded Systems Developers.

Those solutions are great but we think it is very important in all those use cases to optimize performance. To clarify we have to distinguish the most time-consuming tasks in above containers:

• code compilation - there are books about that topic, but since we use mostly Linux, we think that key factor is to have support for ccache and this is our first goal in this post

• packages installation - even when you are using httpredir for apt you still will spent a significant amount of time installing and downloading, because of that it is very important to have locally or on server in LAN apt caching proxy like apt-cacher-ng, we will show how to use it with Docker on build and runtime

ccache

Following example will show ccache usage with xen-docker. Great post about that topic was published by Tim Potter here.

Of course, to use ccache in our container we need it installed, so make sure your Dockerfile contains that package. You can take a look at xen-docker Dockerfile.

I installed ccache on my host to control its content:

cache directory                     /home/pietrushnic/.ccache
primary config                      /home/pietrushnic/.ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
cache hit (direct)                     0
cache hit (preprocessed)               0
cache miss                             0
cache hit rate                      0.00 %
cleanups performed                     0
files in cache                         0
cache size                           0.0 kB
max cache size                       5.0 GB

Moreover it is important to pay attention to directory structure and volumes, because we can easy end up with not working ccache. Of course clear indication that ccache works is that it show some statistics. Configuration of ccache in Docker files should look like this:

ENV PATH="/usr/lib/ccache:${PATH}"
RUN mkdir /home/xen/.ccache && \
	chown xen:xen /home/xen/.ccache

Then to run container with ccache we can pass our ~/.ccache as volume. For single-threaded compilation assuming you checked out correct code and called ./configure:

Before we start testing performance we also have to mention terminology little bit, below we use terms cold cache and hot cache, this was greatly explained on StackOverflow so I will not repeat myself. In short cold means empty and hot means that there are some values from previous runs.

Performance measures

No ccache single-threaded:

docker run --rm -it -v $PWD:/home/xen -w /home/xen 3mdeb/xen-docker \
make debball| ts -s '[%.T]'
(...)
[00:13:10.006206] dpkg-deb: building package 'xen-upstream' in 'xen-upstream-4.8.4.deb'.

No ccache multi-threaded:

docker run --rm -it -v $PWD:/home/xen -w /home/xen 3mdeb/xen-docker \
make -j$(nproc) debball| ts -s '[%.T]'
(...)
[00:07:53.910527] dpkg-deb: building package 'xen-upstream' in 'xen-upstream-4.8.4.deb'.

Let’s make sure ccache is empty

[22:52:57] pietrushnic:~ $ ccache -zcC
Statistics cleared
Cleaned cache
Cleared cache

Cold cache:

docker run --rm -it -e CCACHE_DIR=/home/xen/.ccache -v $PWD:/home/xen  \
-v $HOME/.ccache:/home/xen/.ccache -w /home/xen 3mdeb/xen-docker make -j$(nproc) \
debball | ts -s '[%.T]'
(...)
[00:07:37.440563] dpkg-deb: building package 'xen-upstream' in 'xen-upstream-4.8.4.deb'.

And the stats of ccache:

cache directory                     /home/pietrushnic/.ccache
primary config                      /home/pietrushnic/.ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
stats zero time                     Wed Aug 22 23:29:32 2018
cache hit (direct)                    38
cache hit (preprocessed)              19
cache miss                          3750
cache hit rate                      1.50 %
called for link                      133
called for preprocessing            1498
compiler produced empty output        61
compile failed                         6
preprocessor error                    12
bad compiler arguments                10
unsupported source language            2
autoconf compile/link                 56
unsupported compiler option            2
output to stdout                       4
no input file                       5998
cleanups performed                     0
files in cache                      8887
cache size                         203.1 MB
max cache size                       5.0 GB

Hot cache:

docker run --rm -it -e CCACHE_DIR=/home/xen/.ccache -v $PWD:/home/xen  \
-v $HOME/.ccache:/home/xen/.ccache -w /home/xen 3mdeb/xen-docker make -j$(nproc) \
debball | ts -s '[%.T]'
(...)
[00:05:40.766517] dpkg-deb: building package 'xen-upstream' in 'xen-upstream-4.8.4.deb'.

And the stats of ccache:

cache directory                     /home/pietrushnic/.ccache
primary config                      /home/pietrushnic/.ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
stats zero time                     Wed Aug 22 23:29:32 2018
cache hit (direct)                  3557
cache hit (preprocessed)             229
cache miss                          3767
cache hit rate                     50.13 %
called for link                      266
called for preprocessing            2945
compiler produced empty output       122
compile failed                        12
preprocessor error                    14
bad compiler arguments                14
unsupported source language            4
autoconf compile/link                 64
unsupported compiler option            4
output to stdout                       8
no input file                       8811
cleanups performed                     0
files in cache                      9023
cache size                         204.4 MB
max cache size                       5.0 GB

I’m not ccache expert and cannot explain all results e.g. why hit rate is so low, when we compile the same code?

To conclude, we can gain even 30% with hot cache. Biggest gain we have when using multithreading, but this highly depends on CPU, in my case I had 8 jobs run simultaneously and gain was 40% in compilation time.

apt-cacher-ng

There 2 use case for apt-cacher-ng in our workflows. One is Docker build time, which can be time-consuming since all packages and its dependencies are installed in the base image. Second is runtime, when you need some package that may have extensive dependencies e.g. xen-systema-amd64.

First, let’s setup apt-cacher-ng. Some guide may be found in Docker documentation, but we will modify it a little bit.

Ideally, we would like to use docker compose to set up apt-cacher-ng container whenever it is not set, or have dedicated VM which serves this purpose. In this post, we consider local cache. Dockerfile may look like this:

FROM        ubuntu

RUN     apt-get update && apt-get install -y apt-cacher-ng

EXPOSE      3142
CMD     chmod 777 /var/cache/apt-cacher-ng && /etc/init.d/apt-cacher-ng start && tail -f /var/log/apt-cacher-ng/*

Build and run:

docker build -t apt-cacher .
docker run -d -p 3142:3142 -v $PWD/apt_cache:/var/cache/apt-cacher-ng --name cacher-container apt-cacher
docker logs -f cacher-container

The output should look like this:

* Starting apt-cacher-ng apt-cacher-ng
WARNING: No configuration was read from file:sfnet_mirrors
   ...done.
   ==> /var/log/apt-cacher-ng/apt-cacher.err <==

   ==> /var/log/apt-cacher-ng/apt-cacher.log <==

We should also see that cacher listens on port 3142:

[16:40:01] pietrushnic:~ $ netstat -an |grep 3142
tcp6       0      0 :::3142                 :::*                    LISTEN

Dockerfile should contain following environment variable:

ENV http_proxy ${http_proxy}

Now we can run docker building with appropriate parameters:

docker build --build-arg http_proxy=http://<CACHER_IP>:3142/ -t 3mdeb/xen-docker .| ts -s '[%.T]'

performance measures

xen-docker container build without apt-cacher-ng. To measure what is going on during container build we are using ts from moreutils package.

Without cacher:

docker build -t 3mdeb/xen-docker .| ts -s '[%.S]'
(...)
[00:07:13.723282] Successfully tagged 3mdeb/xen-docker:latest

With cold cache:

docker build --build-arg http_proxy=http://<CACHER_IP>:3142/ -t 3mdeb/xen-docker .| ts -s '[%.T]'
(...)
[00:06:55.051968] Successfully tagged 3mdeb/xen-docker:latest

With hot cache:

docker build --build-arg http_proxy=http://<CACHER_IP>:3142/ -t 3mdeb/xen-docker .| ts -s '[%.T]'
(...)
[00:05:50.237480] Successfully tagged 3mdeb/xen-docker:latest

Assuming that the network conditions did not change between runs to extent of 30s delay we can conclude:

• using cacher even with cold cache is better than nothing, it gives the speedup of about 5%
• using hot cache can spare ~20% of normal container build time, if significant amount of that time is package installation

Of course, those numbers should be confirmed statistically.

Let’s try something more complex

Finally we can try to run much more sophisticated stuff like our debian-rootfs-builder. This code contain mostly compilation and package installation through apt-get.

Initial build statistics were quite bad:

Tuesday 21 August 2018  16:01:58 +0000 (0:00:51.188)       0:42:09.618 ********
===============================================================================
linux-kernel --------------------------------------------------------- 1341.78s
packages -------------------------------------------------------------- 798.20s
debootstrap ----------------------------------------------------------- 327.46s
command ---------------------------------------------------------------- 51.19s
setup ------------------------------------------------------------------- 8.85s
config ------------------------------------------------------------------ 1.93s
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
total ---------------------------------------------------------------- 2529.40s
Tuesday 21 August 2018  16:01:58 +0000 (0:00:51.188)       0:42:09.617 ********
===============================================================================
packages : install packages ------------------------------------------- 798.20s
linux-kernel : make deb-pkg ------------------------------------------- 613.37s
linux-kernel : make deb-pkg ------------------------------------------- 565.16s
debootstrap : debootstrap second stage -------------------------------- 193.23s
debootstrap : debootstrap first stage --------------------------------- 115.25s
compress rootfs -------------------------------------------------------- 51.19s
linux-kernel : make mrproper ------------------------------------------- 30.88s
linux-kernel : decompress Linux "4.9.122" ------------------------------ 22.09s
linux-kernel : decompress Linux "4.14.65" ------------------------------ 20.01s
linux-kernel : get Linux "4.9.122" ------------------------------------- 19.28s
debootstrap : install packages ----------------------------------------- 18.97s
linux-kernel : get Linux "4.14.65" ------------------------------------- 17.15s
linux-kernel : remove everything except artifacts ---------------------- 14.65s
linux-kernel : make mrproper ------------------------------------------- 13.45s
linux-kernel : make olddefconfig ---------------------------------------- 9.12s
linux-kernel : remove everything except artifacts ----------------------- 6.58s
Gathering Facts --------------------------------------------------------- 4.62s
Gathering Facts --------------------------------------------------------- 4.23s
linux-kernel : make olddefconfig ---------------------------------------- 3.94s
linux-kernel : copy bzImage to known location --------------------------- 1.91s
Playbook run took 0 days, 0 hours, 42 minutes, 9 seconds

After adding apt-cacher this improved a lot - 37%!:

Tuesday 21 August 2018  22:48:46 +0000 (0:00:53.340)       0:26:40.226 ********
===============================================================================
linux-kernel --------------------------------------------------------- 1272.91s
debootstrap ----------------------------------------------------------- 265.41s
command ---------------------------------------------------------------- 53.34s
setup ------------------------------------------------------------------- 8.29s
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
total ---------------------------------------------------------------- 1599.95s
Tuesday 21 August 2018  22:48:46 +0000 (0:00:53.341)       0:26:40.225 ********
===============================================================================
linux-kernel : make deb-pkg ------------------------------------------- 608.31s
linux-kernel : make deb-pkg ------------------------------------------- 510.51s
debootstrap : debootstrap second stage -------------------------------- 194.68s
compress rootfs -------------------------------------------------------- 53.34s
debootstrap : debootstrap first stage ---------------------------------- 52.27s
linux-kernel : decompress Linux "4.14.65" ------------------------------ 25.45s
linux-kernel : make mrproper ------------------------------------------- 24.57s
linux-kernel : decompress Linux "4.9.122" ------------------------------ 22.61s
debootstrap : install packages ----------------------------------------- 18.45s
linux-kernel : get Linux "4.14.65" ------------------------------------- 17.44s
linux-kernel : get Linux "4.9.122" ------------------------------------- 16.96s
linux-kernel : make mrproper ------------------------------------------- 12.19s
linux-kernel : make olddefconfig --------------------------------------- 10.54s
linux-kernel : remove everything except artifacts ----------------------- 7.96s
linux-kernel : remove everything except artifacts ----------------------- 7.15s
Gathering Facts --------------------------------------------------------- 4.62s
Gathering Facts --------------------------------------------------------- 3.68s
linux-kernel : make olddefconfig ---------------------------------------- 3.63s
linux-kernel : copy bzImage to known location --------------------------- 1.67s
linux-kernel : copy bzImage to known location --------------------------- 1.58s
Playbook run took 0 days, 0 hours, 26 minutes, 40 seconds

After adding ccache with hot cache:

ccache stats:

cache directory                     /home/pietrushnic/.ccache
primary config                      /home/pietrushnic/.ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
cache hit (direct)                  4595
cache hit (preprocessed)              89
cache miss                          4871
cache hit rate                     49.02 %
called for link                      178
called for preprocessing           12551
compiler produced no output           12
ccache internal error                  2
unsupported code directive            21
no input file                       3687
cleanups performed                     0
files in cache                     14582
cache size                           1.5 GB
max cache size                       5.0 GB

Thursday 23 August 2018  00:41:15 +0000 (0:02:02.608)       0:23:19.962 *******
===============================================================================
linux-kernel ---------------------------------------------------------- 701.42s
packages -------------------------------------------------------------- 246.51s
debootstrap ----------------------------------------------------------- 243.14s
command --------------------------------------------------------------- 123.05s
linux-install ---------------------------------------------------------- 72.47s
setup ------------------------------------------------------------------ 10.10s
config ------------------------------------------------------------------ 3.21s
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
total ---------------------------------------------------------------- 1399.91s
Thursday 23 August 2018  00:41:15 +0000 (0:02:02.608)       0:23:19.961 *******
===============================================================================
linux-kernel : make deb-pkg ------------------------------------------- 388.91s
packages : install packages ------------------------------------------- 246.51s
linux-kernel : make deb-pkg ------------------------------------------- 223.72s
debootstrap : debootstrap second stage -------------------------------- 189.56s
compress rootfs ------------------------------------------------------- 122.61s
linux-install : install Linux "4.14.65" -------------------------------- 37.36s
debootstrap : debootstrap first stage ---------------------------------- 36.00s
linux-install : install Linux "4.9.122" -------------------------------- 35.12s
debootstrap : install packages ----------------------------------------- 17.58s
linux-kernel : get Linux "4.9.122" ------------------------------------- 16.67s
linux-kernel : get Linux "4.14.65" ------------------------------------- 16.18s
linux-kernel : decompress Linux "4.14.65" ------------------------------ 13.82s
linux-kernel : decompress Linux "4.9.122" ------------------------------ 12.72s
linux-kernel : make mrproper -------------------------------------------- 8.21s
linux-kernel : make mrproper -------------------------------------------- 6.55s
Gathering Facts --------------------------------------------------------- 4.81s
linux-kernel : remove everything except artifacts ----------------------- 3.40s
linux-kernel : remove everything except artifacts ----------------------- 3.11s
linux-kernel : make olddefconfig ---------------------------------------- 3.08s
Gathering Facts --------------------------------------------------------- 2.74s
Playbook run took 0 days, 0 hours, 23 minutes, 19 seconds

This is not significant but we gain another 13% and now build time is reasonable. Still most time-consuming tasks belong to compilation and package installation bucket.

Summary

If you have any other ideas about optimizing code compilation or container build time please feel free to comment. If this post will gain popularity we would probably reiterate it with best advices from our readers.

If you looking for Embedded Systems DevOps, who will optimize your firmware or embedded software build environment, look no more and contact us here.