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How To Add Your Build Configuration To LLVM Buildbot Infrastructure
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Introduction
============
This document contains information about adding a build configuration and
buildbot-worker to private worker builder to LLVM Buildbot Infrastructure.
Buildmasters
============
There are two buildmasters running.
* The main buildmaster at `<https://lab.llvm.org/buildbot>`_. All builders
attached to this machine will notify commit authors every time they break
the build.
* The staging buildmaster at `<https://lab.llvm.org/staging>`_. All builders
attached to this machine will be completely silent by default when the build
is broken. This buildmaster is reconfigured every two hours with any new
commits from the llvm-zorg repository.
In order to remain connected to the main buildmaster (and thus notify
developers of failures), a builbot must:
* Be building a supported configuration. Builders for experimental backends
should generally be attached to staging buildmaster.
* Be able to keep up with new commits to the main branch, or at a minimum
recover to tip of tree within a couple of days of falling behind.
Additionally, we encourage all bot owners to point their bots towards the
staging master during maintenance windows, instability troubleshooting, and
such.
Roles & Expectations
====================
Each buildbot has an owner who is the responsible party for addressing problems
which arise with said buildbot. We generally expect the bot owner to be
reasonably responsive.
For some bots, the ownership responsibility is split between a "resource owner"
who provides the underlying machine resource, and a "configuration owner" who
maintains the build configuration. Generally, operational responsibility lies
with the "config owner". We do expect "resource owners" - who are generally
the contact listed in a workers attributes - to proxy requests to the relevant
"config owner" in a timely manner.
Most issues with a buildbot should be addressed directly with a bot owner
via email. Please CC `Galina Kistanova <mailto:[email protected]>`_.
Steps To Add Builder To LLVM Buildbot
=====================================
Volunteers can provide their build machines to work as build workers to
public LLVM Buildbot.
Here are the steps you can follow to do so:
#. Check the existing build configurations to make sure the one you are
interested in is not covered yet or gets built on your computer much
faster than on the existing one. We prefer faster builds so developers
will get feedback sooner after changes get committed.
#. The computer you will be registering with the LLVM buildbot
infrastructure should have all dependencies installed and be able to
build your configuration successfully. Please check what degree
of parallelism (-j param) would give the fastest build. You can build
multiple configurations on one computer.
#. Install buildbot-worker (currently we are using buildbot version 2.8.4).
This specific version can be installed using ``pip``, with a command such
as ``pip3 install buildbot-worker==2.8.4``.
#. Create a designated user account, your buildbot-worker will be running under,
and set appropriate permissions.
#. Choose the buildbot-worker root directory (all builds will be placed under
it), buildbot-worker access name and password the build master will be using
to authenticate your buildbot-worker.
#. Create a buildbot-worker in context of that buildbot-worker account. Point it
to the **lab.llvm.org** port **9994** (see `Buildbot documentation,
Creating a worker
<http://docs.buildbot.net/current/tutorial/firstrun.html#creating-a-worker>`_
for more details) by running the following command:
.. code-block:: bash
$ buildbot-worker create-worker <buildbot-worker-root-directory> \
lab.llvm.org:9994 \
<buildbot-worker-access-name> \
<buildbot-worker-access-password>
Only once a new worker is stable, and
approval from Galina has been received (see last step) should it
be pointed at the main buildmaster.
Now start the worker:
.. code-block:: bash
$ buildbot-worker start <buildbot-worker-root-directory>
This will cause your new worker to connect to the staging buildmaster
which is silent by default.
Try this once then check the log file
``<buildbot-worker-root-directory>/worker/twistd.log``. If your settings
are correct you will see a refused connection. This is good and expected,
as the credentials have not been established on both ends. Now stop the
worker and proceed to the next steps.
#. Fill the buildbot-worker description and admin name/e-mail. Here is an
example of the buildbot-worker description::
Windows 7 x64
Core i7 (2.66GHz), 16GB of RAM
g++.exe (TDM-1 mingw32) 4.4.0
GNU Binutils 2.19.1
cmake version 2.8.4
Microsoft(R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86
See `here <http://docs.buildbot.net/current/manual/installation/worker.html>`_
for which files to edit.
#. Send a patch which adds your build worker and your builder to
`zorg <https://github.com/llvm/llvm-zorg>`_. Use the typical LLVM
`workflow <https://llvm.org/docs/Contributing.html#how-to-submit-a-patch>`_.
* workers are added to ``buildbot/osuosl/master/config/workers.py``
* builders are added to ``buildbot/osuosl/master/config/builders.py``
Please make sure your builder name and its builddir are unique through the
file.
All new builders should default to using the "'collapseRequests': False"
configuration. This causes the builder to build each commit individually
and not merge build requests. To maximize quality of feedback to developers,
we *strongly prefer* builders to be configured not to collapse requests.
This flag should be removed only after all reasonable efforts have been
exhausted to improve build times such that the builder can keep up with
commit flow.
It is possible to allow email addresses to unconditionally receive
notifications on build failure; for this you'll need to add an
``InformativeMailNotifier`` to ``buildbot/osuosl/master/config/status.py``.
This is particularly useful for the staging buildmaster which is silent
otherwise.
#. Send the buildbot-worker access name and the access password directly to
`Galina Kistanova <mailto:[email protected]>`_, and wait until she
lets you know that your changes are applied and buildmaster is
reconfigured.
#. Make sure you can start the buildbot-worker and successfully connect
to the silent buildmaster. Then set up your buildbot-worker to start
automatically at the start up time. See the buildbot documentation
for help. You may want to restart your computer to see if it works.
#. Check the status of your buildbot-worker on the `Waterfall Display (Staging)
<http://lab.llvm.org/staging/#/waterfall>`_ to make sure it is
connected, and the `Workers Display (Staging)
<http://lab.llvm.org/staging/#/workers>`_ to see if administrator
contact and worker information are correct.
#. At this point, you have a working builder connected to the staging
buildmaster. You can now make sure it is reliably green and keeps
up with the build queue. No notifications will be sent, so you can
keep an unstable builder connected to staging indefinitely.
#. (Optional) Once the builder is stable on the staging buildmaster with
several days of green history, you can choose to move it to the production
buildmaster to enable developer notifications. Please email `Galina
Kistanova <mailto:[email protected]>`_ for review and approval.
To move a worker to production (once approved), stop your worker, edit the
buildbot.tac file to change the port number from 9994 to 9990 and start it
again.
Best Practices for Configuring a Fast Builder
=============================================
As mentioned above, we generally have a strong preference for
builders which can build every commit as they come in. This section
includes best practices and some recommendations as to how to achieve
that end.
The goal
In 2020, the monorepo had just under 35 thousand commits. This works
out to an average of 4 commits per hour. Already, we can see that a
builder must cycle in less than 15 minutes to have a hope of being
useful. However, those commits are not uniformly distributed. They
tend to cluster strongly during US working hours. Looking at a couple
of recent (Nov 2021) working days, we routinely see ~10 commits per
hour during peek times, with occasional spikes as high as ~15 commits
per hour. Thus, as a rule of thumb, we should plan for our builder to
complete ~10-15 builds an hour.
Resource Appropriately
At 10-15 builds per hour, we need to complete a new build on average every
4 to 6 minutes. For anything except the fastest of hardware/build configs,
this is going to be well beyond the ability of a single machine. In buildbot
terms, we likely going to need multiple workers to build requests in parallel
under a single builder configuration. For some rough back of the envelope
numbers, if your build config takes e.g. 30 minutes, you will need something
on the order of 5-8 workers. If your build config takes ~2 hours, you'll
need something on the order of 20-30 workers. The rest of this section
focuses on how to reduce cycle times.
Restrict what you build and test
Think hard about why you're setting up a bot, and restrict your build
configuration as much as you can. Basic functionality is probably
already covered by other bots, and you don't need to duplicate that
testing. You only need to be building and testing the *unique* parts
of the configuration. (e.g. For a multi-stage clang builder, you probably
don't need to be enabling every target or building all the various utilities.)
It can sometimes be worthwhile splitting a single builder into two or more,
if you have multiple distinct purposes for the same builder. As an example,
if you want to both a) confirm that all of LLVM builds with your host
compiler, and b) want to do a multi-stage clang build on your target, you
may be better off with two separate bots. Splitting increases resource
consumption, but makes it easy for each bot to keep up with commit flow.
Additionally, splitting bots may assist in triage by narrowing attention to
relevant parts of the failing configuration.
In general, we recommend Release build types with Assertions enabled. This
generally provides a good balance between build times and bug detection for
most buildbots. There may be room for including some debug info (e.g. with
`-gmlt`), but in general the balance between debug info quality and build
times is a delicate one.
Use Ninja & LLD
Ninja really does help build times over Make, particularly for highly
parallel builds. LLD helps to reduce both link times and memory usage
during linking significantly. With a build machine with sufficient
parallelism, link times tend to dominate critical path of the build, and are
thus worth optimizing.
Use CCache and NOT incremental builds
Using ccache materially improves average build times. Incremental builds
can be slightly faster, but introduce the risk of build corruption due to
e.g. state changes, etc... At this point, the recommendation is not to
use incremental builds and instead use ccache as the latter captures the
majority of the benefit with less risk of false positives.
One of the non-obvious benefits of using ccache is that it makes the
builder less sensitive to which projects are being monitored vs built.
If a change triggers a build request, but doesn't change the build output
(e.g. doc changes, python utility changes, etc..), the build will entirely
hit in cache and the build request will complete in just the testing time.
With multiple workers, it is tempting to try to configure a shared cache
between the workers. Experience to date indicates this is difficult to
well, and that having local per-worker caches gets most of the benefit
anyways. We don't currently recommend shared caches.
CCache does depend on the builder hardware having sufficient IO to access
the cache with reasonable access times - i.e. a fast disk, or enough memory
for a RAM cache, etc.. For builders without, incremental may be your best
option, but is likely to require higher ongoing involvement from the
sponsor.
Enable batch builds
As a last resort, you can configure your builder to batch build requests.
This makes the build failure notifications markedly less actionable, and
should only be done once all other reasonable measures have been taken.
Leave it on the staging buildmaster
While most of this section has been biased towards builders intended for
the main buildmaster, it is worth highlighting that builders can run
indefinitely on the staging buildmaster. Such a builder may still be
useful for the sponsoring organization, without concern of negatively
impacting the broader community. The sponsoring organization simply
has to take on the responsibility of all bisection and triage.
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