зеркало из https://github.com/mozilla/gecko-dev.git
277 строки
12 KiB
ReStructuredText
277 строки
12 KiB
ReStructuredText
======================
|
|
TaskGraph Mach Command
|
|
======================
|
|
|
|
The task graph is built by linking different kinds of tasks together, pruning
|
|
out tasks that are not required, then optimizing by replacing subgraphs with
|
|
links to already-completed tasks.
|
|
|
|
Concepts
|
|
--------
|
|
|
|
* *Task Kind* - Tasks are grouped by kind, where tasks of the same kind do not
|
|
have interdependencies but have substantial similarities, and may depend on
|
|
tasks of other kinds. Kinds are the primary means of supporting diversity,
|
|
in that a developer can add a new kind to do just about anything without
|
|
impacting other kinds.
|
|
|
|
* *Task Attributes* - Tasks have string attributes by which can be used for
|
|
filtering. Attributes are documented in :doc:`attributes`.
|
|
|
|
* *Task Labels* - Each task has a unique identifier within the graph that is
|
|
stable across runs of the graph generation algorithm. Labels are replaced
|
|
with TaskCluster TaskIds at the latest time possible, facilitating analysis
|
|
of graphs without distracting noise from randomly-generated taskIds.
|
|
|
|
* *Optimization* - replacement of a task in a graph with an equivalent,
|
|
already-completed task, or a null task, avoiding repetition of work.
|
|
|
|
Kinds
|
|
-----
|
|
|
|
Kinds are the focal point of this system. They provide an interface between
|
|
the large-scale graph-generation process and the small-scale task-definition
|
|
needs of different kinds of tasks. Each kind may implement task generation
|
|
differently. Some kinds may generate task definitions entirely internally (for
|
|
example, symbol-upload tasks are all alike, and very simple), while other kinds
|
|
may do little more than parse a directory of YAML files.
|
|
|
|
A ``kind.yml`` file contains data about the kind, as well as referring to a
|
|
Python class implementing the kind in its ``implementation`` key. That
|
|
implementation may rely on lots of code shared with other kinds, or contain a
|
|
completely unique implementation of some functionality.
|
|
|
|
The full list of pre-defined keys in this file is:
|
|
|
|
``implementation``
|
|
Class implementing this kind, in the form ``<module-path>:<object-path>``.
|
|
This class should be a subclass of ``taskgraph.kind.base:Kind``.
|
|
|
|
``kind-dependencies``
|
|
Kinds which should be loaded before this one. This is useful when the kind
|
|
will use the list of already-created tasks to determine which tasks to
|
|
create, for example adding an upload-symbols task after every build task.
|
|
|
|
Any other keys are subject to interpretation by the kind implementation.
|
|
|
|
The result is a nice segmentation of implementation so that the more esoteric
|
|
in-tree projects can do their crazy stuff in an isolated kind without making
|
|
the bread-and-butter build and test configuration more complicated.
|
|
|
|
Dependencies
|
|
------------
|
|
|
|
Dependencies between tasks are represented as labeled edges in the task graph.
|
|
For example, a test task must depend on the build task creating the artifact it
|
|
tests, and this dependency edge is named 'build'. The task graph generation
|
|
process later resolves these dependencies to specific taskIds.
|
|
|
|
Decision Task
|
|
-------------
|
|
|
|
The decision task is the first task created when a new graph begins. It is
|
|
responsible for creating the rest of the task graph.
|
|
|
|
The decision task for pushes is defined in-tree, in ``.taskcluster.yml``. That
|
|
task description invokes ``mach taskcluster decision`` with some metadata about
|
|
the push. That mach command determines the optimized task graph, then calls
|
|
the TaskCluster API to create the tasks.
|
|
|
|
Note that this mach command is *not* designed to be invoked directly by humans.
|
|
Instead, use the mach commands described below, supplying ``parameters.yml``
|
|
from a recent decision task. These commands allow testing everything the
|
|
decision task does except the command-line processing and the
|
|
``queue.createTask`` calls.
|
|
|
|
Graph Generation
|
|
----------------
|
|
|
|
Graph generation, as run via ``mach taskgraph decision``, proceeds as follows:
|
|
|
|
#. For all kinds, generate all tasks. The result is the "full task set"
|
|
#. Create dependency links between tasks using kind-specific mechanisms. The
|
|
result is the "full task graph".
|
|
#. Filter the target tasks (based on a series of filters, such as try syntax,
|
|
tree-specific specifications, etc). The result is the "target task set".
|
|
#. Based on the full task graph, calculate the transitive closure of the target
|
|
task set. That is, the target tasks and all requirements of those tasks.
|
|
The result is the "target task graph".
|
|
#. Optimize the target task graph based on kind-specific optimization methods.
|
|
The result is the "optimized task graph" with fewer nodes than the target
|
|
task graph.
|
|
#. Create tasks for all tasks in the optimized task graph.
|
|
|
|
Transitive Closure
|
|
..................
|
|
|
|
Transitive closure is a fancy name for this sort of operation:
|
|
|
|
* start with a set of tasks
|
|
* add all tasks on which any of those tasks depend
|
|
* repeat until nothing changes
|
|
|
|
The effect is this: imagine you start with a linux32 test job and a linux64 test job.
|
|
In the first round, each test task depends on the test docker image task, so add that image task.
|
|
Each test also depends on a build, so add the linux32 and linux64 build tasks.
|
|
|
|
Then repeat: the test docker image task is already present, as are the build
|
|
tasks, but those build tasks depend on the build docker image task. So add
|
|
that build docker image task. Repeat again: this time, none of the tasks in
|
|
the set depend on a task not in the set, so nothing changes and the process is
|
|
complete.
|
|
|
|
And as you can see, the graph we've built now includes everything we wanted
|
|
(the test jobs) plus everything required to do that (docker images, builds).
|
|
|
|
Optimization
|
|
------------
|
|
|
|
The objective of optimization to remove as many tasks from the graph as
|
|
possible, as efficiently as possible, thereby delivering useful results as
|
|
quickly as possible. For example, ideally if only a test script is modified in
|
|
a push, then the resulting graph contains only the corresponding test suite
|
|
task.
|
|
|
|
A task is said to be "optimized" when it is either replaced with an equivalent,
|
|
already-existing task, or dropped from the graph entirely.
|
|
|
|
A task can be optimized if all of its dependencies can be optimized and none of
|
|
its inputs have changed. For a task on which no other tasks depend (a "leaf
|
|
task"), the optimizer can determine what has changed by looking at the
|
|
version-control history of the push: if the relevant files are not modified in
|
|
the push, then it considers the inputs unchanged. For tasks on which other
|
|
tasks depend ("non-leaf tasks"), the optimizer must replace the task with
|
|
another, equivalent task, so it generates a hash of all of the inputs and uses
|
|
that to search for a matching, existing task.
|
|
|
|
In some cases, such as try pushes, tasks in the target task set have been
|
|
explicitly requested and are thus excluded from optimization. In other cases,
|
|
the target task set is almost the entire task graph, so targetted tasks are
|
|
considered for optimization. This behavior is controlled with the
|
|
``optimize_target_tasks`` parameter.
|
|
|
|
Action Tasks
|
|
------------
|
|
|
|
Action Tasks are tasks which help you to schedule new jobs via Treeherder's
|
|
"Add New Jobs" feature. The Decision Task creates a YAML file named
|
|
``action.yml`` which can be used to schedule Action Tasks after suitably replacing
|
|
``{{decision_task_id}}`` and ``{{task_labels}}``, which correspond to the decision
|
|
task ID of the push and a comma separated list of task labels which need to be
|
|
scheduled.
|
|
|
|
This task invokes ``mach taskgraph action-task`` which builds up a task graph of
|
|
the requested tasks. This graph is optimized using the tasks running initially in
|
|
the same push, due to the decision task.
|
|
|
|
So for instance, if you had already requested a build task in the ``try`` command,
|
|
and you wish to add a test which depends on this build, the original build task
|
|
is re-used.
|
|
|
|
Action Tasks are currently scheduled by
|
|
[pulse_actions](https://github.com/mozilla/pulse_actions). This feature is only
|
|
present on ``try`` pushes for now.
|
|
|
|
Mach commands
|
|
-------------
|
|
|
|
A number of mach subcommands are available aside from ``mach taskgraph
|
|
decision`` to make this complex system more accesssible to those trying to
|
|
understand or modify it. They allow you to run portions of the
|
|
graph-generation process and output the results.
|
|
|
|
``mach taskgraph tasks``
|
|
Get the full task set
|
|
|
|
``mach taskgraph full``
|
|
Get the full task graph
|
|
|
|
``mach taskgraph target``
|
|
Get the target task set
|
|
|
|
``mach taskgraph target-graph``
|
|
Get the target task graph
|
|
|
|
``mach taskgraph optimized``
|
|
Get the optimized task graph
|
|
|
|
Each of these commands taskes a ``--parameters`` option giving a file with
|
|
parameters to guide the graph generation. The decision task helpfully produces
|
|
such a file on every run, and that is generally the easiest way to get a
|
|
parameter file. The parameter keys and values are described in
|
|
:doc:`parameters`; using that information, you may modify an existing
|
|
``parameters.yml`` or create your own.
|
|
|
|
Task Parameterization
|
|
---------------------
|
|
|
|
A few components of tasks are only known at the very end of the decision task
|
|
-- just before the ``queue.createTask`` call is made. These are specified
|
|
using simple parameterized values, as follows:
|
|
|
|
``{"relative-datestamp": "certain number of seconds/hours/days/years"}``
|
|
Objects of this form will be replaced with an offset from the current time
|
|
just before the ``queue.createTask`` call is made. For example, an
|
|
artifact expiration might be specified as ``{"relative-timestamp": "1
|
|
year"}``.
|
|
|
|
``{"task-reference": "string containing <dep-name>"}``
|
|
The task definition may contain "task references" of this form. These will
|
|
be replaced during the optimization step, with the appropriate taskId for
|
|
the named dependency substituted for ``<dep-name>`` in the string.
|
|
Multiple labels may be substituted in a single string, and ``<<>`` can be
|
|
used to escape a literal ``<``.
|
|
|
|
Taskgraph JSON Format
|
|
---------------------
|
|
|
|
Task graphs -- both the graph artifacts produced by the decision task and those
|
|
output by the ``--json`` option to the ``mach taskgraph`` commands -- are JSON
|
|
objects, keyed by label, or for optimized task graphs, by taskId. For
|
|
convenience, the decision task also writes out ``label-to-taskid.json``
|
|
containing a mapping from label to taskId. Each task in the graph is
|
|
represented as a JSON object.
|
|
|
|
Each task has the following properties:
|
|
|
|
``task_id``
|
|
The task's taskId (only for optimized task graphs)
|
|
|
|
``label``
|
|
The task's label
|
|
|
|
``attributes``
|
|
The task's attributes
|
|
|
|
``dependencies``
|
|
The task's in-graph dependencies, represented as an object mapping
|
|
dependency name to label (or to taskId for optimized task graphs)
|
|
|
|
``task``
|
|
The task's TaskCluster task definition.
|
|
|
|
``kind_implementation``
|
|
The module and the class name which was used to implement this particular task.
|
|
It is always of the form ``<module-path>:<object-path>``
|
|
|
|
The results from each command are in the same format, but with some differences
|
|
in the content:
|
|
|
|
* The ``tasks`` and ``target`` subcommands both return graphs with no edges.
|
|
That is, just collections of tasks without any dependencies indicated.
|
|
|
|
* The ``optimized`` subcommand returns tasks that have been assigned taskIds.
|
|
The dependencies array, too, contains taskIds instead of labels, with
|
|
dependencies on optimized tasks omitted. However, the ``task.dependencies``
|
|
array is populated with the full list of dependency taskIds. All task
|
|
references are resolved in the optimized graph.
|
|
|
|
The output of the ``mach taskgraph`` commands are suitable for processing with
|
|
the `jq <https://stedolan.github.io/jq/>`_ utility. For example, to extract all
|
|
tasks' labels and their dependencies:
|
|
|
|
.. code-block:: shell
|
|
|
|
jq 'to_entries | map({label: .value.label, dependencies: .value.dependencies})'
|
|
|