Patchbot: AI bot making use of Natural Language Processing to suggest backports
=============================================================== 2023-12-18 ====


Background
----------

Selecting patches to backport from the development branch is a tedious task, in
part due to the abundance of patches and the fact that many bug fixes are for
that same version and not for backporting. The more it gets delayed, the harder
it becomes, and the harder it is to start, the less likely it gets started. The
urban legend along which one "just" has to do that periodically doesn't work
because certain patches need to be left hanging for a while under observation,
others need to be merged urgently, and for some, the person in charge of the
backport might simply need an opinion from the patch's author or the affected
subsystem maintainer, and this cannot make the whole backport process stall.

The information needed to figure if a patch needs to be backported is present
in the commit message, with varying nuances such as "may", "may not", "should",
"probably", "shouldn't unless", "keep under observation" etc. One particularly
that is specific to backports is that the opinion on a patch may change over
time, either because it was later found to be wrong or insufficient, or because
the former analysis mistakenly suggested to backport or not to.

This means that the person in charge of the backports has to read the whole
commit message for each patch, to figure the backporting instructions, and this
takes a while.

Several attempts were made over the years to try to partially automate this
task, including the cherry-pick mode of the "git-show-backports" utility that
eases navigation back-and-forth between commits.

Lately, a lot of progress was made in the domain of Natural Language
Understanding (NLU) and more generally Natural Language Processing (NLP). Since
the first attempts in early 2023 involving successive layers of the Roberta
model, called from totally unreliable Python code, and December 2023, the
situation evolved from promising but unusable to mostly autonomous.

For those interested in history, the first attempts in early 2023 involved
successive layers of the Roberta model, but these were relying on totally
unreliable Python code that broke all the time and could barely be transferred
to another machine without upgrading or downgrading the installed modules, and
it used to use huge amounts of resources for a somewhat disappointing result:
the verdicts were correct roughly 60-70% of the time, it was not possible to
get hints such as "wait" nor even "uncertain".  It could just be qualified as
promising. Another big limitation was the limit to 256 tokens, forcing the
script to select only the last few lines of the commit message to take the
decision. Roughly at the same time, in March 2023 Meta issued their much larger
LLaMa model, and Georgi Gerganov released "llama.cpp", an open-source C++
engine that loads and runs such large models without all the usual problems
inherent to the Python ecosystem. New attempts were made with LLaMa and it was
already much better than Roberta, but the output was difficult to parse, and it
required to be combined with the final decision layer of Roberta. Then new
variants of LLaMa appeared such as Alpaca, which follows instructions, but
tends to forget them if given before the patch, then Vicuna which was pretty
reliable but very slow at 33B size and difficult to tune, then Airoboros,
which was the first one to give very satisfying results in a reasonable time,
following instructions reasonably closely with a stable output, but with
sometimes surprising analysis and contradictions. It was already about 90%
reliable and considered as a time saver in 13B size. Other models were later
tried as they appeared such as OpenChat-3.5, Juna, OpenInstruct, Orca-2,
Mistral-0.1 and it variants Neural and OpenHermes-2.5. Mistral showed an
unrivaled understanding despite being smaller and much faster than other ones,
but was a bit freewheeling regarding instructions. Dolphin-2.1 rebased on top
of it gave extremely satisfying results, with less variations in the output
format, but still the script had difficulties trying to catch its conclusion
from time to time, though it was pretty much readable for the human in charge
of the task. And finally just before releasing, Mistral-0.2 was released and
addressed all issues, with a human-like understanding and perfectly obeying
instructions, providing an extremely stable output format that is easy to parse
from simple scripts. The decisions now match the human's ones in close to 100%
of the patches, unless the human is aware of extra context, of course.


Architecture
------------

The current solution relies on the llama.cpp engine, which is a simple, fast,
reliable and portable engine to load models and run inference, and the
Mistral-0.2 LLM.

A collection of patches is built from the development branch since the -dev0
tag, and for each of them, the engine is called to evaluate the developer's
intent based on the commit message. A detailed context explaining the haproxy
maintenance model and what the user wants is passed, then the LLM is invited to
provide its opinion on the need for a backport and an explanation of the reason
for its choice. This often helps the user to find a quick summary about the
patch. All these outputs are then converted to a long HTML page with colors and
radio buttons, where patches are preselected based on this classification,
that the user can consult and adjust, read the commits if needed, and the
selected patches finally provide some copy-pastable commands in a text-area to
select commit IDs to work on, typically in a form that's suitable for a simple
"git cherry-pick -sx".

The scripts are designed to be able to run on a headless machine, called from a
crontab and with the output served from a static HTTP server.

The code is currently found from Georgi Gerganov's repository:

   https://github.com/ggerganov/llama.cpp

Tag b1505 is known to work fine, and uses the GGUF file format.

The model(s) can be found on Hugging Face user "TheBloke"'s collection of
models:

   https://huggingface.co/TheBloke

Model Mistral-7B-Instruct-v0.2-GGUF quantized at Q5K_M is known to work well
with the llama.cpp version above.


Deployment
----------

Note: it is a good idea to start to download the model(s) in the background as
      such files are typically 5 GB or more and can take some time to download
      depending on the internet bandwidth.

It seems reasonable to create a dedicated user to periodically run this task.
Let's call it "patchbot". Developers should be able to easily run a shell from
this user to perform some maintenance or testing (e.g. "sudo").

All paths are specified in the example "update-3.0.sh" script, and assume a
deployment in the user's home, so this is what is being described here. The
proposed deployment layout is the following:

  $HOME (e.g. /home/patchbot)
    |
    +- data
    |  |
    |  +-- models   # GGUF files from TheBloke's collection
    |  |
    |  +-- prompts  # prompt*-pfx*, prompt*-sfx*, cache
    |  |
    |  +-- in
    |  |   |
    |  |   +-- haproxy      # haproxy Git repo
    |  |   |
    |  |   +-- patches-3.0  # patches from development branch 3.0
    |  |
    |  +-- out              # report directory (HTML)
    |
    +- prog
    |  |
    |  +-- bin              # program(s)
    |  |
    |  +-- scripts          # processing scripts
    |  |
    |  +-- llama.cpp        # llama Git repository


- Let's first create the structure:

    mkdir -p ~/data/{in,models,prompts} ~/prog/{bin,scripts}

- data/in/haproxy must contain a clone of the haproxy development tree that
  will periodically be pulled from:

    cd ~/data/in
    git clone https://github.com/haproxy/haproxy
    cd ~

- The prompt files are a copy of haproxy's "dev/patchbot/prompt/" subdirectory.
  The prompt files are per-version because they contain references to the
  haproxy development version number. For each prompt, there is a prefix
  ("-pfx"), that is loaded before the patch, and a suffix ("-sfx") that
  precises the user's expectations after reading the patch. For best efficiency
  it's useful to place most of the explanation in the prefix and the least
  possible in the suffix, because the prefix is cacheable. Different models
  will use different instructions formats and different explanations, so it's
  fine to keep a collection of prompts and use only one. Different instruction
  formats are commonly used, "llama-2", "alpaca", "vicuna", "chatml" being
  common. When experimenting with a new model, just copy-paste the closest one
  and tune it for best results. Since we already cloned haproxy above, we'll
  take the files from there:

    cp ~/data/in/haproxy/dev/patchbot/prompt/*txt ~/data/prompts/

  Upon first run, a cache file will be produced in this directory by parsing
  an empty file and saving the current model's context. The cache file will
  automatically be deleted and rebuilt if it is absent or older than the prefix
  or suffix file. The cache files are specific to a model so when experimenting
  with other models, be sure not to reuse the same cache file, or in doubt,
  just delete them. Rebuilding the cache file typically takes around 2 minutes
  of processing on a 8-core machine.

- The model(s) from TheBloke's Hugging Face account have to be downloaded in
  GGUF file format, quantized at Q5K_M, and stored as-is into data/models/.

- data/in/patches-3.0/ is where the "mk-patch-list.sh" script will emit the
  patches corresponding to new commits in the development branch. Its suffix
  must match the name of the current development branch for patches to be found
  there. In addition, the classification of the patches will be emitted there
  next to the input patches, with the same name as the original file with a
  suffix indicating what model/prompt combination was used.

    mkdir -p ~/data/in/patches-3.0

- data/out is where the final report will be emitted. If running on a headless
  machine, it is worth making sure that this directory is accessible from a
  static web server. Thus either create a directory and place a symlink or
  configuration somewhere in the web server's settings to reference this
  location, or make it a symlink to another place already exported by the web
  server and make sure the user has the permissions to write there.

    mkdir -p ~/data/out

  On Ubuntu-20.04 it was found that the package "micro-httpd" works out of the
  box serving /var/www/html and follows symlinks. As such this is sufficient to
  expose the reports:

    sudo ln -s ~patchbot/data/out /var/www/html/patchbot

- prog/bin will contain the executable(s) needed to operate, namely "main" from
  llama.cpp:

    mkdir -p ~/prog/bin

- prog/llama.cpp is a clone of the "llama.cpp" GitHub repository. As of
  december 2023, the project has improved its forward compatibility and it's
  generally both safe and recommended to stay on the last version, hence to
  just clone the master branch. In case of difficulties, tag b1505 was proven
  to work well with the aforementioned model. Building is done by default for
  the local platform, optimised for speed with native CPU.

    mkdir -p ~/prog
    cd ~/prog
    git clone https://github.com/ggerganov/llama.cpp
    [ only in case of problems:  cd llama.cpp && git checkout b1505 ]

    make -j$(nproc) main LLAMA_FAST=1
    cp main ~/prog/bin/
    cd ~

- prog/scripts needs the following scripts:
  - mk-patch-list.sh from haproxy's scripts/ subdirectory
  - submit-ai.sh, process-*.sh, post-ai.sh, update-*.sh

    cp ~/data/in/haproxy/scripts/mk-patch-list.sh  ~/prog/scripts/
    cp ~/data/in/haproxy/dev/patchbot/scripts/*.sh ~/prog/scripts/

  - verify that the various paths in update-3.0.sh match your choices, or
    adjust them:

    vi ~/prog/scripts/update-3.0.sh

  - the tool is memory-bound, so a machine with more memory channels and/or
    very fast memory will usually be faster than a higher CPU count with a
    lower memory bandwidth. In addition, the performance is not linear with
    the number of cores and experimentation shows that efficiency drops above
    8 threads. For this reason the script integrates a "PARALLEL_RUNS" variable
    indicating how many instances to run in parallel, each on its own patch.
    This allows to make better use of the CPUs and memory bandwidth. Setting
    2 instances for 8 cores / 16 threads gives optimal results on dual memory
    channel systems.

From this point, executing this update script manually should work and produce
the result. Count around 0.5-2 mn per patch on a 8-core machine, so it can be
reasonably fast during the early development stages (before -dev1) but
unbearably long later, where it can make more sense to run it at night. It
should not report any error and should only report the total execution time.

If interrupted (Ctrl-C, logout, out of memory etc), check for incomplete .txt
files in ~/data/in/patches*/ that can result from this interruption, and delete
them because they will not be reproduced:

    ls -lart ~/data/in/patches-3.0/*.txt
    ls -lS ~/data/in/patches-3.0/*.txt

Once the output is produced, visit ~/data/out/ using a web browser and check
that the table loads correctly. Note that after a new release or a series of
backports, the table may appear empty, it's just because all known patches are
already backported and collapsed by default. Clicking on "All" at the top left
will unhide them.

Finally when satisfied, place it in a crontab, for example, run every hour:

    crontab -e

    # m h  dom mon dow   command
    # run every hour at minute 02
    2 * * * * /home/patchbot/update-3.0.sh


Usage
-----

Using the HTML output is a bit rustic but efficient. The interface is split in
5 columns from left to right:

  - first column: patch number from 1 to N, just to ease navigation. Below the
    number appears a radio button which allows to mark this patch as the start
    of the review. When clicked, all prior patches disappear and are not listed
    anymore. This can be undone by clicking on the radio button under the "All"
    word in this column's header.


  - second column: commit ID (abbreviated "CID" in the header). It's a 8-digit
    shortened representation of the commit ID. It's presented as a link, which,
    if clicked, will directly show that commit from the haproxy public
    repository. Below the commit ID is the patch's author date in condensed
    format "DD-MmmYY", e.g. "18-Dec23" for "18th December 2023". It was found
    that having a date indication sometimes helps differentiate certain related
    patches.

  - third column: "Subject", this is the subject of the patch, prefixed with
    the 4-digit number matching the file name in the directory (e.g. helps to
    remove or reprocess one if needed). This is also a link to the same commit
    in the haproxy's public repository. At the lower right under the subject
    is the shortened e-mail address (only user@domain keeping only the first
    part of the domain, e.g. "foo@haproxy"). Just like with the date, it helps
    figuring what to expect after a recent discussion with a developer.

  - fourth column: "Verdict". This column contains 4 radio buttons prefiguring
    the choice for this patch between "N" for "No", represented in gray (this
    patch should not be backported, let's drop it), "U" for "Uncertain" in
    green (still unsure about it, most likely the author should be contacted),
    "W" for "Wait" in blue (this patch should be backported but not
    immediately, only after it has spent some time in the development branch),
    and "Y" for "Yes" in red (this patch must be backported, let's pick it).
    The choice is preselected by the scripts above, and since these are radio
    buttons, the user is free to change this selection. Reloading will lose the
    user's choices. When changing a selection, the line's background changes to
    match a similar color tone, allowing to visually spot preselected patches.

  - fifth column: reason for the choice. The scripts try to provide an
    explanation for the choice of the preselection, and try to always end with
    a conclusion among "yes", "no", "wait", "uncertain". The explanation
    usually fits in 2-4 lines and is faster to read than a whole commit message
    and very often pretty accurate. It's also been noticed that Mistral-v0.2
    shows much less hallucinations than others (it doesn't seem to invent
    information that was not part of its input), so seeing certain topics being
    discussed there generally indicate that they were in the original commit
    message. The scripts try to emphasize the sensitive parts of the commit
    message such as risks, dependencies, referenced issues, oldest version to
    backport to, etc. Elements that look like issues numbers and commit IDs are
    turned to links to ease navigation.

In addition, in order to improve readability, the top of the table shows 4
buttons allowing to show/hide each category. For example, when trying to focus
only on "uncertain" and "wait", it can make sense to hide "N" and "Y" and click
"Y" or "N" on the displayed ones until there is none anymore.

In order to reduce the risk of missing a misqualified patch, those marked "BUG"
or "DOC" are displayed in bold even if tagged "No". It has been shown to be
sufficient to catch the eye when scrolling and encouraging to re-visit them.

More importantly, the script will try to also check which patches were already
backported to the previous stable version. Those that were backported will have
the first two columns colored gray, and by default, the review will start from
the first patch after the last backported one. This explains why just after a
backport, the table may appear empty with only the footer "New" checked.

Finally, at the bottom of the table is an editable, copy-pastable text area
that is redrawn at each click. It contains a series of 4 shell commands that
can be copy-pasted at once and assign commit IDs to 4 variables, one per
category. Most often only "y" will be of interest, so for example if the
review process ends with:

    cid_y=( 7dab3e82 456ba6e9 75f5977f 917f7c74 )

Then copy-pasting it in a terminal already in the haproxy-2.9 directory and
issuing:

    git cherry-pick -sx ${cid_y[@]}

Will result in all these patches to be backported to that version.


Criticisms
----------

The interface is absolutely ugly but gets the job done. Proposals to revamp it
are welcome, provided that they do not alter usability and portability (e.g.
the ability to open the locally produced file without requiring access to an
external server).


Thanks
------

This utility is the proof that boringly repetitive tasks that can be offloaded
from humans can save their time to do more productive things. This work which
started with extremely limited tools was made possible thanks to Meta, for
opening their models after leaking it, Georgi Gerganov and the community that
developed around llama.cpp, for creating the first really open engine that
builds out of the box and just works, contrary to the previous crippled Python-
only ecosystem, Tom Jobbins (aka TheBloke) for making it so easy to discover
new models every day by simply quantizing all of them and making them available
from a single location, MistralAI for producing an exceptionally good model
that surpasses all others, is the first one to feel as smart and accurate as a
real human on such tasks, is fast, and totally free, and of course, HAProxy
Technologies for investing some time on this and for the available hardware
that permits a lot of experimentation.
