=====================
SimGrid was conceived as a tool to study distributed algorithms. Its
-modern :ref:`S4U interface <S4U_doc>` makes it easy to assess Cloud,
-P2P, HPC, IoT and similar settings.
+:ref:`S4U interface <S4U_doc>` makes it easy to assess Cloud,
+P2P, HPC, IoT, and other similar settings (:ref:`more info <index>`).
A typical SimGrid simulation is composed of several |Actors|_, that
execute user-provided functions. The actors have to explicitly use the
-S4U interface to express their computation, communication, disk usage
-and other |Activities|_, so that they get reflected within the
+S4U interface to express their computation, communication, disk usage,
+and other |Activities|_ so that they get reflected within the
simulator. These activities take place on **Resources** (|Hosts|_,
|Links|_, |Disks|_). SimGrid predicts the time taken by each
activity and orchestrates accordingly the actors waiting for the
Each actor executes a user-provided function on a simulated |Host|_
with which it can interact. Communications are not directly sent to
-actors, but posted onto a |Mailbox|_ that serve as rendez-vous point
+actors, but posted onto a |Mailbox|_ that serves as a rendez-vous point
between communicating actors.
.. |Actors| replace:: **Actors**
.. _Mutex: app_s4u.html#s4u-mutex
**In the remainder of this tutorial**, you will discover a simple yet
-fully functioning example of SimGrid simulation: the Master/Workers
-application. We will detail each part of the code and necessary
-configuration to make it working. After this tour, several exercises
+fully-functioning example of SimGrid simulation: the Master/Workers
+application. We will detail each part of the code and the necessary
+configuration to make it work. After this tour, several exercises
are proposed to let you discover some of the SimGrid features, hands
-on the keyboard. This practical session will be given in C++, that you
-are supposed to know beforehand.
+on the keyboard. This practical session will be given in C++ or Python,
+which you are supposed to know beforehand.
Discover the Master/Workers
---------------------------
-This section introduces a first example of SimGrid simulation. This
-simple application is composed of two kind of actors: the **master**
+This section introduces an example of SimGrid simulation. This
+simple application is composed of two kinds of actors: the **master**
is in charge of distributing some computational tasks to a set of
**workers** that execute them.
.. image:: /tuto_s4u/img/intro.svg
:align: center
-We first present a round-robin version of this application, where the
-master dispatches the tasks to the workers, one after the other, until
-all tasks are dispatched. Later in this tutorial, you will be given
-the opportunity to improve this scheme.
+The provided code dispatches these tasks in `round-robin scheduling <https://en.wikipedia.org/wiki/Round-robin_scheduling>`_,
+i.e. in circular order: tasks are dispatched to each worker one after the other, until all tasks are dispatched.
+You will improve this scheme later in this tutorial.
The Actors
..........
-Let's start with the code of the worker. It is represented by the
+Let's start with the code of the master. It is represented by the
*master* function below. This simple function takes at least 3
-parameters (the amount of tasks to dispatch, their computational size
-in flops to compute and their communication size in bytes to
-exchange). Every parameter after the third one must be the name of an
+parameters (the number of tasks to dispatch, their computational size
+in flops to compute, and their communication size in bytes to
+exchange). Every parameter after the third one must be the name of a
host on which a worker is waiting for something to compute.
Then, the tasks are sent one after the other, each on a mailbox named
after the worker's hosts. On the other side, a given worker (which
-code is given below) wait for incoming tasks on its own
-mailbox.
+code is given below) waits for incoming tasks on its mailbox.
-
-At the end, once all tasks are dispatched, the master dispatches
+In the end, once all tasks are dispatched, the master dispatches
another task per worker, but this time with a negative amount of flops
to compute. Indeed, this application decided by convention, that the
workers should stop when encountering such a negative compute_size.
-At the end of the day, the only SimGrid specific functions used in
-this example are :cpp:func:`simgrid::s4u::Mailbox::by_name` and
-:cpp:func:`simgrid::s4u::Mailbox::put`. Also, :c:macro:`XBT_INFO` is used
-as a replacement to printf() or to cout to ensure that the messages
-are nicely logged along with the simulated time and actor name.
+ .. tabs::
+
+ .. group-tab:: C++
+
+ At the end of the day, the only SimGrid specific functions used in
+ this example are :cpp:func:`simgrid::s4u::Mailbox::by_name` (to retrieve or create a mailbox) and
+ :cpp:func:`simgrid::s4u::Mailbox::put` (so send something over a mailbox). Also, :c:macro:`XBT_INFO` is used
+ as a replacement to ``printf()`` or ``std::cout`` to ensure that the messages
+ are nicely logged along with the simulated time and actor name.
+
+ .. literalinclude:: ../../examples/cpp/app-masterworkers/s4u-app-masterworkers-fun.cpp
+ :language: c++
+ :start-after: master-begin
+ :end-before: master-end
+ .. group-tab:: Python
-.. literalinclude:: ../../examples/s4u/app-masterworkers/s4u-app-masterworkers-fun.cpp
- :language: c++
- :start-after: master-begin
- :end-before: master-end
+ At the end of the day, the only SimGrid specific functions used in
+ this example are :py:func:`simgrid.Mailbox.by_name` (to retrieve or create a mailbox) and
+ :py:func:`simgrid.Mailbox.put` (so send something over a mailbox). Also, :py:func:`simgrid.this_actor.info` is used
+ as a replacement to `print` to ensure that the messages
+ are nicely logged along with the simulated time and actor name.
-Here comes the code of the worker actors. This function expects no
+ .. literalinclude:: ../../examples/python/app-masterworkers/app-masterworkers.py
+ :language: python
+ :start-after: master-begin
+ :end-before: master-end
+
+Then comes the code of the worker actors. This function expects no
parameter from its vector of strings. Its code is very simple: it
-expects messages on the mailbox that is named after its own host. As long as it gets valid
-computation requests (whose compute_amount is positive), it compute
+expects messages on the mailbox that is named after its host. As long as it gets valid
+computation requests (whose compute_amount is positive), it computes
this task and waits for the next one.
-The worker retrieves its own host with
-:cpp:func:`simgrid::s4u::this_actor::get_host`. The
-:ref:`simgrid::s4u::this_actor <API_s4u_this_actor>`
-namespace contains many such helping functions.
+.. tabs::
+
+ .. group-tab:: C++
+
+ The worker retrieves its own host with
+ :cpp:func:`simgrid::s4u::this_actor::get_host`. The
+ :ref:`simgrid::s4u::this_actor <API_s4u_this_actor>`
+ namespace contains many such helping functions.
+
+ .. literalinclude:: ../../examples/cpp/app-masterworkers/s4u-app-masterworkers-fun.cpp
+ :language: c++
+ :start-after: worker-begin
+ :end-before: worker-end
-.. literalinclude:: ../../examples/s4u/app-masterworkers/s4u-app-masterworkers-fun.cpp
- :language: c++
- :start-after: worker-begin
- :end-before: worker-end
+ .. group-tab:: Python
+
+ The worker retrieves its own host with :py:func:`simgrid.this_actor.get_host`. The
+ :ref:`this_actor <API_s4u_this_actor>` object contains many such helping functions.
+
+ .. literalinclude:: ../../examples/python/app-masterworkers/app-masterworkers.py
+ :language: python
+ :start-after: worker-begin
+ :end-before: worker-end
Starting the Simulation
.......................
-And this is it. In only a few lines, we defined the algorithm of our
-master/workers examples.
+And this is it. In only a few lines, we defined the algorithm of our master/workers example.
+
+.. tabs::
+
+ .. group-tab:: C++
+
+ That being said, an algorithm alone is not enough to define a
+ simulation: SimGrid is a library, not a program. So you need to define
+ your own ``main()`` function as follows. This function is in charge of
+ creating a SimGrid simulation engine (on line 3), register the actor
+ functions to the engine (on lines 7 and 8), load the simulated platform
+ from its description file (on line 11), map actors onto that platform
+ (on line 12) and run the simulation until its completion on line 15.
+
+ .. literalinclude:: ../../examples/cpp/app-masterworkers/s4u-app-masterworkers-fun.cpp
+ :language: c++
+ :start-after: main-begin
+ :end-before: main-end
+ :linenos:
+
+ .. group-tab:: Python
-That being said, an algorithm alone is not enough to define a
-simulation: SimGrid is a library, not a program. So you need to define
-your own ``main()`` function as follows. This function is in charge of
-creating a SimGrid simulation engine (on line 3), register the actor
-functions to the engine (on lines 7 and 8), load the simulated platform
-from its description file (on line 11), map actors onto that platform
-(on line 12) and run the simulation until its completion on line 15.
+ That being said, an algorithm alone is not enough to define a simulation:
+ you need a main block to setup the simulation and its components as follows.
+ This code creates a SimGrid simulation engine (on line 4), registers the actor
+ functions to the engine (on lines 7 and 8), loads the simulated platform
+ from its description file (on line 11), map actors onto that platform
+ (on line 12) and run the simulation until its completion on line 15.
-.. literalinclude:: ../../examples/s4u/app-masterworkers/s4u-app-masterworkers-fun.cpp
- :language: c++
- :start-after: main-begin
- :end-before: main-end
- :linenos:
+ .. literalinclude:: ../../examples/python/app-masterworkers/app-masterworkers.py
+ :language: python
+ :start-after: main-begin
+ :end-before: main-end
+ :linenos:
-As you can see, this also requires a platform file and a deployment
-file.
+Finally, this example requires a platform file and a deployment file.
Platform File
.............
Platform files define the simulated platform on which the provided
-application will take place. In contains one or several **Network
-Zone** |api_s4u_NetZone|_ that contain both |Host|_ and |Link|_
+application will take place. It contains one or several **Network
+Zone** |api_s4u_NetZone|_ that contains both |Host|_ and |Link|_
Resources, as well as routing information.
Such files can get rather long and boring, so the example below is
-only an excerpts of the full ``examples/platforms/small_platform.xml``
-file. For example, most routing information are missing, and only the
+only an excerpt of the full ``examples/platforms/small_platform.xml``
+file. For example, most routing information is missing, and only the
route between the hosts Tremblay and Fafard is given. This path
-traverses 6 links (named 4, 3, 2, 0, 1 and 8). There are several
+traverses 6 links (named 4, 3, 2, 0, 1, and 8). There are several
examples of platforms in the archive under ``examples/platforms``.
.. |api_s4u_NetZone| image:: /img/extlink.png
...............
Deployment files specify the execution scenario: it lists the actors
-that should be started, along with their parameter. In the following
+that should be started, along with their parameters. In the following
example, we start 6 actors: one master and 5 workers.
-.. literalinclude:: ../../examples/s4u/app-masterworkers/s4u-app-masterworkers_d.xml
+.. literalinclude:: ../../examples/cpp/app-masterworkers/s4u-app-masterworkers_d.xml
:language: xml
Execution Example
.................
-This time, we have all parts: once the program is compiled, we can
-execute it as follows. Note how the XBT_INFO() requests turned into
-informative messages.
+This time, we have all parts: once the program is compiled, we can execute it as follows.
-.. "WARNING: Over dedent has detected" is expected here as we remove the $ marker this way
+.. tabs::
-.. literalinclude:: ../../examples/s4u/app-masterworkers/s4u-app-masterworkers.tesh
- :language: shell
- :start-after: s4u-app-masterworkers-fun
- :prepend: $$$ ./masterworkers platform.xml deploy.xml
- :append: $$$
- :dedent: 2
+ .. group-tab:: C++
+
+ Note how the :c:macro:`XBT_INFO` requests turned into informative messages.
+
+ .. "WARNING: non-whitespace stripped by dedent" is expected here as we remove the $ marker this way
+
+ .. literalinclude:: ../../examples/cpp/app-masterworkers/s4u-app-masterworkers.tesh
+ :language: shell
+ :start-after: s4u-app-masterworkers-fun
+ :prepend: $$$ ./masterworkers platform.xml deploy.xml
+ :append: $$$
+ :dedent: 2
+
+ .. group-tab:: Python
+
+ Note how the :py:func:`simgrid.this_actor.info` calls turned into informative messages.
+
+ .. literalinclude:: ../../examples/python/app-masterworkers/app-masterworkers.tesh
+ :language: shell
+ :start-after: app-masterworkers_d.xml
+ :prepend: $$$ python ./app-masterworkers.py platform.xml deploy.xml
+ :append: $$$
+ :dedent: 2
+
+Each example included in the SimGrid distribution comes with a `tesh`
+file that presents how to start the example once compiled, along with
+the expected output. These files are used for the automatic testing of
+the framework but can be used to see the examples' output without
+compiling them. See e.g. the file
+`examples/cpp/app-masterworkers/s4u-app-masterworkers.tesh <https://framagit.org/simgrid/simgrid/-/blob/master/examples/cpp/app-masterworkers/s4u-app-masterworkers.tesh>`_.
+Lines starting with `$` are the commands to execute;
+lines starting with `>` are the expected output of each command, while
+lines starting with `!` are configuration items for the test runner.
Improve it Yourself
-------------------
In this section, you will modify the example presented earlier to
-explore the quality of the proposed algorithm. For now, it works and
+explore the quality of the proposed algorithm. It already works, and
the simulation prints things, but the truth is that we have no idea of
whether this is a good algorithm to dispatch tasks to the workers.
This very simple setting raises many interesting questions:
load balancing will likely get uneven, in particular when
distributing the last tasks.
-- How does the quality of such algorithm dependent on the platform
+- How does the quality of such an algorithm dependent on the platform
characteristics and on the task characteristics?
Whenever the input communication time is very small compared to
may be quite complicated. How does such a topology impact the
previous result?
- When data transfers are the bottleneck, it is likely that a good
+ When data transfers are the bottleneck, it is likely that good
modeling of the platform becomes essential. The SimGrid platform
models are particularly handy to account for complex platform
topologies.
- What is the best applicative topology?
- Is a flat master worker deployment sufficient? Should we go for a
+ Is a flat master-worker deployment sufficient? Should we go for a
hierarchical algorithm, with some forwarders taking large pools of
tasks from the master, each of them distributing their tasks to a
sub-pool of workers? Or should we introduce super-peers,
- How is such an algorithm sensitive to external workload variation?
- What if bandwidth, latency and computing speed can vary with no
+ What if bandwidth, latency, and computing speed can vary with no
warning? Shouldn't you study whether your algorithm is sensitive
to such load variations?
giant? With SimGrid, you can focus on your algorithm. The whole
simulation mechanism is already working.
-Here is the visualization of a SimGrid simulation of two master worker
+Here is the visualization of a SimGrid simulation of two master-worker
applications (one in light gray and the other in dark gray) running in
concurrence and showing resource usage over a long period of time. It
was obtained with the Triva software.
Using Docker
............
-The easiest way to take the tutorial is to use the dedicated Docker
-image. Once you `installed Docker itself
-<https://docs.docker.com/install/>`_, simply do the following:
+The easiest way to take the tutorial is to use the dedicated Docker image.
+Once you `installed Docker itself <https://docs.docker.com/install/>`_, simply do the following:
-.. code-block:: shell
+.. code-block:: console
- docker pull simgrid/tuto-s4u
- docker run -it --rm --name simgrid --volume ~/simgrid-tutorial:/source/tutorial simgrid/tuto-s4u bash
+ $ docker pull simgrid/tuto-s4u
+ $ mkdir ~/simgrid-tutorial
+ $ docker run --user $UID:$GID -it --rm --name simgrid --volume ~/simgrid-tutorial:/source/tutorial simgrid/tuto-s4u bash
This will start a new container with all you need to take this
tutorial, and create a ``simgrid-tutorial`` directory in your home on
when you log out of the container, so don't edit the other files!
All needed dependencies are already installed in this container
-(SimGrid, a C++ compiler, cmake, pajeng and R). Vite being only
+(SimGrid, a C++ compiler, CMake, pajeng, and R). Vite being only
optional in this tutorial, it is not installed to reduce the image
size.
in the image. You should copy it to your working directory and
recompile it when you first log in:
-.. code-block:: shell
+.. code-block:: console
- cp -r /source/simgrid-template-s4u.git/* /source/tutorial
- cd /source/tutorial
- cmake .
- make
+ $ cp -r /source/simgrid-template-s4u.git/* /source/tutorial
+ $ cd /source/tutorial
+ $ cmake .
+ $ make
Using your Computer Natively
............................
-To take the tutorial on your machine, you first need to :ref:`install
-a recent version of SimGrid <install>`, a C++ compiler and also
-``pajeng`` to visualize the traces. You may want to install `Vite
-<http://vite.gforge.inria.fr/>`_ to get a first glance at the traces.
-The provided code template requires cmake to compile. On Debian and
-Ubuntu for example, you can get them as follows:
+.. tabs::
-.. code-block:: shell
+ .. group-tab:: C++
- sudo apt install simgrid pajeng cmake g++ vite
+ To take the tutorial on your machine, you first need to :ref:`install
+ a recent version of SimGrid <install>`, a C++ compiler, and also
+ ``pajeng`` to visualize the traces. You may want to install `Vite
+ <http://vite.gforge.inria.fr/>`_ to get a first glance at the traces.
+ The provided code template requires CMake to compile. On Debian and
+ Ubuntu for example, you can get them as follows:
-For R analysis of the produced traces, you may want to install R,
-and the `pajengr <https://github.com/schnorr/pajengr#installation/>`_ package.
+ .. code-block:: console
+
+ $ sudo apt install simgrid pajeng cmake g++ vite
+
+ An initial version of the source code is provided on framagit. This
+ template compiles with CMake. If SimGrid is correctly installed, you
+ should be able to clone the `repository
+ <https://framagit.org/simgrid/simgrid-template-s4u>`_ and recompile
+ everything as follows:
+
+ .. code-block:: console
+
+ # (exporting SimGrid_PATH is only needed if SimGrid is installed in a non-standard path)
+ $ export SimGrid_PATH=/where/to/simgrid
+
+ $ git clone https://framagit.org/simgrid/simgrid-template-s4u.git
+ $ cd simgrid-template-s4u/
+ $ cmake .
+ $ make
+
+ If you struggle with the compilation, then you should double-check
+ your :ref:`SimGrid installation <install>`. On need, please refer to
+ the :ref:`Troubleshooting your Project Setup
+ <install_yours_troubleshooting>` section.
-.. code-block:: shell
+ .. group-tab:: Python
- sudo apt install r-base r-cran-devtools cmake flex bison
- Rscript -e "library(devtools); install_github('schnorr/pajengr');"
+ To take the tutorial on your machine, you first need to :ref:`install
+ a recent version of SimGrid <install>` and ``pajeng`` to visualize the
+ traces. You may want to install `Vite <http://vite.gforge.inria.fr/>`_ to get a first glance at the traces.
+ On Debian and Ubuntu for example, you can get them as follows:
-An initial version of the source code is provided on framagit. This
-template compiles with cmake. If SimGrid is correctly installed, you
-should be able to clone the `repository
-<https://framagit.org/simgrid/simgrid-template-s4u>`_ and recompile
-everything as follows:
+ .. code-block:: console
-.. code-block:: shell
+ $ sudo apt install simgrid pajeng vite
- # (exporting SimGrid_PATH is only needed if SimGrid is installed in a non-standard path)
- export SimGrid_PATH=/where/to/simgrid
+ An initial version of the source code is provided on framagit.
+ If SimGrid is correctly installed, you should be able to clone the `repository
+ <https://framagit.org/simgrid/simgrid-template-s4u>`_ and execute it as follows:
- git clone https://framagit.org/simgrid/simgrid-template-s4u.git
- cd simgrid-template-s4u/
- cmake .
- make
+ .. code-block:: console
+
+ $ git clone https://framagit.org/simgrid/simgrid-template-s4u.git
+ $ cd simgrid-template-s4u/
+ $ python master-workers.py small_platform.xml master-workers_d.xml
+
+ If you get some errors, then you should double-check
+ your :ref:`SimGrid installation <install>`. On need, please refer to
+ the :ref:`Troubleshooting your Project Setup <install_yours_troubleshooting>` section.
+
+
+For R analysis of the produced traces, you may want to install R
+and the `pajengr <https://github.com/schnorr/pajengr#installation/>`_ package.
+
+.. code-block:: console
+
+ # install R and necessary packages
+ $ sudo apt install r-base r-cran-devtools r-cran-tidyverse
+ # install pajengr dependencies
+ $ sudo apt install git cmake flex bison
+ # install the pajengr R package
+ $ Rscript -e "library(devtools); install_github('schnorr/pajengr');"
-If you struggle with the compilation, then you should double check
-your :ref:`SimGrid installation <install>`. On need, please refer to
-the :ref:`Troubleshooting your Project Setup
-<install_yours_troubleshooting>` section.
Discovering the Provided Code
.............................
-Please compile and execute the provided simulator as follows:
+.. tabs::
+
+ .. group-tab:: C++
-.. code-block:: shell
+ Please compile and execute the provided simulator as follows:
- make master-workers
- ./master-workers small_platform.xml master-workers_d.xml
+ .. code-block:: console
+
+ $ make master-workers
+ $ ./master-workers small_platform.xml master-workers_d.xml
+
+ .. group-tab:: Python
+
+ Please execute the provided simulator as follows:
+
+ .. code-block:: console
+
+ $ python master-workers.py small_platform.xml master-workers_d.xml
For a more "fancy" output, you can use simgrid-colorizer.
-.. code-block:: shell
+.. code-block:: console
+
+ # Run C++ code
+ $ ./master-workers small_platform.xml master-workers_d.xml 2>&1 | simgrid-colorizer
- ./master-workers small_platform.xml master-workers_d.xml 2>&1 | simgrid-colorizer
+ # Run Python code
+ $ python master-workers.py small_platform.xml master-workers_d.xml 2>&1 | simgrid-colorizer
If you installed SimGrid to a non-standard path, you may have to
specify the full path to simgrid-colorizer on the above line, such as
``/opt/simgrid/bin/simgrid-colorizer``. If you did not install it at all,
you can find it in <simgrid_root_directory>/bin/colorize.
-For a classical Gantt-Chart vizualisation, you can use `Vite
+For a classical Gantt-Chart visualization, you can use `Vite
<http://vite.gforge.inria.fr/>`_ if you have it installed, as
follows. But do not spend too much time installing Vite, because there
is a better way to visualize SimGrid traces (see below).
-.. code-block:: shell
+.. code-block:: console
+
+ # Run C++ code
+ $ ./master-workers small_platform.xml master-workers_d.xml --cfg=tracing:yes --cfg=tracing/actor:yes
+ # Run Python code
+ $ python master-workers.py small_platform.xml master-workers_d.xml --cfg=tracing:yes --cfg=tracing/actor:yes
- ./master-workers small_platform.xml master-workers_d.xml --cfg=tracing:yes --cfg=tracing/msg/process:yes
- vite simgrid.trace
+ # Visualize the produced trace
+ $ vite simgrid.trace
.. image:: /tuto_s4u/img/vite-screenshot.png
:align: center
+.. note::
+
+ If you use an older version of SimGrid (before v3.26), you should use
+ ``--cfg=tracing/msg/process:yes`` instead of ``--cfg=tracing/actor:yes``.
+
If you want the full power to visualize SimGrid traces, you need
to use R. As a start, you can download this `starter script
<https://framagit.org/simgrid/simgrid/raw/master/docs/source/tuto_s4u/draw_gantt.R>`_
and use it as follows:
-.. code-block:: shell
+.. code-block:: console
- ./master-workers small_platform.xml master-workers_d.xml --cfg=tracing:yes --cfg=tracing/msg/process:yes
- Rscript draw_gantt.R simgrid.trace
+ # Run C++ code
+ $ ./master-workers small_platform.xml master-workers_d.xml --cfg=tracing:yes --cfg=tracing/actor:yes
+ # Run Python code
+ $ python master-workers.py small_platform.xml master-workers_d.xml --cfg=tracing:yes --cfg=tracing/actor:yes
+
+ # Visualize the produced trace
+ $ Rscript draw_gantt.R simgrid.trace
It produces a ``Rplots.pdf`` with the following content:
:align: center
-Lab 1: Simpler Deployments
+Lab 1: Simpler deployments
--------------------------
+.. rst-class:: learning-goals
+
+ **Learning goals:**
+
+ * Get your hands on the code and change the communication pattern
+ * Discover the Mailbox mechanism
+
In the provided example, adding more workers quickly becomes a pain:
-You need to start them (at the bottom of the file), and to inform the
+You need to start them (at the bottom of the file) and inform the
master of its availability with an extra parameter. This is mandatory
if you want to inform the master of where the workers are running. But
actually, the master does not need to have this information.
we could use their ID (which should be filled in one location
only).
-This could be done with the following deployment file. It's clearly
+This could be done with the following deployment file. It's
not shorter than the previous one, but it's still simpler because the
information is only written once. It thus follows the `DRY
<https://en.wikipedia.org/wiki/Don't_repeat_yourself>`_ `SPOT
.. literalinclude:: tuto_s4u/deployment1.xml
:language: xml
+.. tabs::
+
+ .. group-tab:: C++
-Copy your ``master-workers.cpp`` into ``master-workers-lab1.cpp`` and
-add a new executable into ``CMakeLists.txt``. Then modify your worker
-function so that it gets its mailbox name not from the name of its
-host, but from the string passed as ``args[1]``. The master will send
-messages to all workers based on their number, for example as follows:
+ Copy your ``master-workers.cpp`` into ``master-workers-lab1.cpp`` and
+ add a new executable into ``CMakeLists.txt``. Then modify your worker
+ function so that it gets its mailbox name not from the name of its
+ host, but from the string passed as ``args[1]``. The master will send
+ messages to all workers based on their number, for example as follows:
-.. code-block:: cpp
+ .. code-block:: cpp
- for (int i = 0; i < tasks_count; i++) {
- std::string worker_rank = std::to_string(i % workers_count);
- std::string mailbox_name = std::string("worker-") + worker_rank;
- simgrid::s4u::Mailbox* mailbox = simgrid::s4u::Mailbox::by_name(mailbox_name);
+ for (int i = 0; i < tasks_count; i++) {
+ std::string worker_rank = std::to_string(i % workers_count);
+ std::string mailbox_name = std::string("worker-") + worker_rank;
+ simgrid::s4u::Mailbox* mailbox = simgrid::s4u::Mailbox::by_name(mailbox_name);
- mailbox->put(...);
+ mailbox->put(...);
- ...
- }
+ ...
+ }
+ .. group-tab:: Python
+
+ Copy your ``master-workers.py`` into ``master-workers-lab1.py`` then
+ modify your worker
+ function so that it gets its mailbox name not from the name of its
+ host, but from the string passed as ``args[0]``. The master will send
+ messages to all workers based on their number, for example as follows:
+
+ .. code-block:: cpp
+
+ for i in range(tasks_count):
+ mailbox = Mailbox.by_name(str(i % worker_count))
+ mailbox.put(...)
Wrap up
.......
The mailboxes are a very powerful mechanism in SimGrid, allowing many
-interesting application settings. They may feel surprising if you are
+interesting application settings. They may feel unusual if you are
used to BSD sockets or other classical systems, but you will soon
-appreciate their power. They are only used to match the
-communications, but have no impact on the communication
+appreciate their power. They are only used to match
+communications but have no impact on the communication
timing. ``put()`` and ``get()`` are matched regardless of their
initiators' location and then the real communication occurs between
the involved parties.
-Please refer to the full `Mailboxes' documentation
-<app_s4u.html#s4u-mailbox>`_ for more details.
+Please refer to the full `Mailboxes' documentation <app_s4u.html#s4u-mailbox>`_
+for more details.
Lab 2: Using the Whole Platform
-------------------------------
-It is now easier to add a new worker, but you still has to do it
+.. rst-class:: learning-goals
+
+ **Learning goals:**
+
+ * Interact with the platform (get the list of all hosts)
+ * Create actors directly from your program instead of the deployment file
+
+It is now easier to add a new worker, but you still have to do it
manually. It would be much easier if the master could start the
workers on its own, one per available host in the platform. The new
deployment file should be as simple as:
Creating the workers from the master
....................................
-For that, the master needs to retrieve the list of hosts declared in
-the platform with :cpp:func:`simgrid::s4u::Engine::get_all_hosts`.
-Then, the master should start the worker actors with
-:cpp:func:`simgrid::s4u::Actor::create`.
+.. tabs::
+
+ .. group-tab:: C++
-``Actor::create(name, host, func, params...)`` is a very flexible
-function. Its third parameter is the function that the actor should
-execute. This function can take any kind of parameter, provided that
-you pass similar parameters to ``Actor::create()``. For example, you
-could have something like this:
+ For that, the master needs to retrieve the list of hosts declared in
+ the platform with :cpp:func:`simgrid::s4u::Engine::get_all_hosts`.
+ Then, the master should start the worker actors with
+ :cpp:func:`simgrid::s4u::Actor::create`.
-.. code-block:: cpp
+ ``Actor::create(name, host, func, params...)`` is a very flexible
+ function. Its third parameter is the function that the actor should
+ execute. This function can take any kind of parameter, provided that
+ you pass similar parameters to ``Actor::create()``. For example, you
+ could have something like this:
- void my_actor(int param1, double param2, std::string param3) {
- ...
- }
- int main(int argc, char argv**) {
- ...
- simgrid::s4u::ActorPtr actor;
- actor = simgrid::s4u::Actor::create("name", simgrid::s4u::Host::by_name("the_host"),
- &my_actor, 42, 3.14, "thevalue");
- ...
- }
+ .. code-block:: cpp
+
+ void my_actor(int param1, double param2, std::string param3) {
+ ...
+ }
+ int main(int argc, char argv**) {
+ ...
+ simgrid::s4u::ActorPtr actor;
+ actor = simgrid::s4u::Actor::create("name", simgrid::s4u::Host::by_name("the_host"),
+ &my_actor, 42, 3.14, "thevalue");
+ ...
+ }
+
+ .. group-tab:: Python
+
+ For that, the master needs to retrieve the list of hosts declared in
+ the platform with :py:func:`simgrid.Engine.get_all_hosts`. Since this method is not static,
+ you may want to call it on the Engine instance, as in ``Engine.instance().get_all_hosts()``.
+ Then, the master should start the worker actors with :py:func:`simgrid.Actor.create`.
+
+ ``Actor.create(name, host, func, params...)`` is a very flexible
+ function. Its third parameter is the function that the actor should
+ execute. This function can take any kind of parameter, provided that
+ you pass similar parameters to ``Actor.create()``. For example, you
+ could have something like this:
+
+ .. code-block:: python
+
+ def my_actor(param1, param2, param3):
+ # your code comes here
+ actor = simgrid.Actor.create("name", the_host, my_actor, 42, 3.14, "thevalue")
Master-Workers Communication
use a mailbox name that is unique over the simulation even if there is
more than one master.
-One possibility for that is to use the actor ID (aid) of each worker
-as a mailbox name. The master can retrieve the aid of the newly
-created actor with ``actor->get_pid()`` while the actor itself can
-retrieve its own aid with ``simgrid::s4u::this_actor::get_pid()``.
-The retrieved value is an ``aid_t``, which is an alias for ``long``.
-
-Instead of having one mailbox per worker, you could also reorganize
-completely your application to have only one mailbox per master. All
-the workers of a given master would pull their work from the same
-mailbox, which should be passed as parameter to the workers. This
-reduces the amount of mailboxes, but prevents the master from taking
-any scheduling decision. It really depends on how you want to organize
-your application and what you want to study with your simulator. In
-this tutorial, that's probably not a good idea.
+.. tabs::
+
+ .. group-tab:: C++
+
+ One possibility for that is to use the actor ID (aid) of each worker
+ as a mailbox name. The master can retrieve the aid of the newly
+ created actor with :cpp:func:`simgrid::s4u::Actor::get_pid()` while the actor itself can
+ retrieve its own aid with :cpp:func:`simgrid::s4u::this_actor::get_pid()`.
+ The retrieved value is an :cpp:type:`aid_t`, which is an alias for ``long``.
+
+ .. group-tab:: Python
+
+ One possibility for that is to use the actor ID of each worker
+ as a mailbox name. The master can retrieve the aid of the newly
+ created actor with :py:func:`simgrid.Actor.pid` while the actor itself can
+ retrieve its own aid with :py:func:`simgrid.this_actor.get_pid()`.
Wrap up
.......
In this exercise, we reduced the amount of configuration that our
-simulator requests. This is both a good idea, and a dangerous
+simulator requests. This is both a good idea and a dangerous
trend. This simplification is another application of the good old DRY/SPOT
programming principle (`Don't Repeat Yourself / Single Point Of Truth
<https://en.wikipedia.org/wiki/Don%27t_repeat_yourself>`_), and you
But at the same time, you should be careful in separating your
scientific contribution (the master/workers algorithm) and the
-artifacts used to test it (platform, deployment and workload). This is
+artifacts used to test it (platform, deployment, and workload). This is
why SimGrid forces you to express your platform and deployment files
in XML instead of using a programming interface: it forces a clear
-separation of concerns between things of very different nature.
+separation of concerns between things of different nature.
Lab 3: Fixed Experiment Duration
--------------------------------
+.. rst-class:: learning-goals
+
+ **Learning goals:**
+
+ * Forcefully kill actors, and stop the simulation at a given point of time
+ * Control the logging verbosity
+
In the current version, the number of tasks is defined through the
worker arguments. Hence, tasks are created at the very beginning of
the simulation. Instead, have the master dispatching tasks for a
-predetermined amount of time. The tasks must now be created on demand
+predetermined amount of time. The tasks must now be created on need
instead of beforehand.
Of course, usual time functions like ``gettimeofday`` will give you the
-time on your real machine, which is prety useless in the
+time on your real machine, which is pretty useless in the
simulation. Instead, retrieve the time in the simulated world with
-:cpp:func:`simgrid::s4u::Engine::get_clock`.
+:cpp:func:`simgrid::s4u::Engine::get_clock` (C++) or
+:py:func:`simgrid.Engine.get_clock()`) (Python).
You can still stop your workers with a specific task as previously,
-or you may kill them forcefully with
-:cpp:func:`simgrid::s4u::Actor::kill` (if you already have a reference
-to the actor you want to kill) or
-:cpp:func:`void simgrid::s4u::Actor::kill(aid_t)` (if you only have its ID).
-
+or you may kill them forcefully with :cpp:func:`simgrid::s4u::Actor::kill` (C++)
+:py:func:`simgrid.Actor.kill` (Python).
Anyway, the new deployment `deployment3.xml` file should thus look
like this:
.................................
Not all messages are equally informative, so you probably want to
-change some of the ``XBT_INFO`` into ``XBT_DEBUG`` so that they are
-hidden by default. For example, you may want to use ``XBT_INFO`` once
-every 100 tasks and ``XBT_DEBUG`` when sending all the other tasks. Or
+change some of the *info* messages (C: :c:macro:`XBT_INFO`; Python: :py:func:`simgrid.this_actor.info`)
+into *debug* messages`(C: :c:macro:`XBT_DEBUG`; Python: :py:func:`simgrid.this_actor.debug`) so that they are
+hidden by default. For example, you may want to use an *info* message once
+every 100 tasks and *debug* when sending all the other tasks. Or
you could show only the total number of tasks processed by
default. You can still see the debug messages as follows:
-.. code-block:: shell
+.. code-block:: console
+
+ $ ./master-workers-lab3 small_platform.xml deployment3.xml --log=s4u_app_masterworker.thres:debug
+
+Lab 4: What-if analysis
+-----------------------
+
+.. rst-class:: learning-goals
+
+ **Learning goals:**
+
+ * Change the platform characteristics during the simulation.
+ * Explore other communication patterns.
+
+.. todo::
+
+ Some of the required functions are not implemented in Python yet. You can detect that if the method name is not a link to the documentation.
+
+Computational speed
+...................
+
+Attach a profile to your hosts, so that their computational speed automatically vary over time, modeling an external load on these machines.
+This can be done with :cpp:func:`simgrid::s4u::Host::set_speed_profile` (C++) or :py:func:`simgrid.Host.set_speed_profile` (python).
+
+Make it so that one of the hosts get really really slow, and observe how your whole application performance decreases.
+This is because one slow host slows down the whole process. Instead of a round-robin dispatch push,
+you should completely reorganize your application in a First-Come First-Served manner (FCFS).
+Actors should pull a task whenever they are ready, so that fast actors can overpass slow ones in the queue.
+
+There is two ways to implement that: either the workers request a task to the master by sending their name to a specific mailbox,
+or the master directly pushes the tasks to a centralized mailbox from which the workers pull their work. The first approach is closer
+to what would happen with communications based on BSD sockets while the second is closer to message queues. You could also decide to
+model your socket application in the second manner if you want to neglect these details and keep your simulator simple. It's your decision.
+
+Changing the communication schema can be a bit hairy, but once it works, you will see that such as simple FCFS schema allows one to greatly
+increase the amount of tasks handled over time here. Things may be different with another platform file.
+
+Communication speed
+...................
+
+Let's now modify the communication speed between hosts.
- ./master-workers-lab3 small_platform.xml deployment3.xml --log=msg_test.thres:debug
+Retrieve a link from its name with :cpp:func:`simgrid::s4u::Link::by_name()` (C++) or :py:func:`simgrid.Link.by_name()` (python).
+Retrieve all links in the platform with :cpp:func:`simgrid::s4u::Engine::get_all_links()` (C++) or :py:func:`simgrid.Engine.get_all_links()` (python).
-Lab 4: Competing Applications
+Retrieve the list of links from one host to another with :cpp:func:`simgrid::s4u::Host::route_to` (C++) or :py:func:`simgrid.Host.route_to` (python).
+
+Modify the bandwidth of a given link with :cpp:func:`simgrid::s4u::Link::set_bandwidth` (C++) or :py:func:`simgrid.Link.set_bandwidth` (python).
+You can even have the bandwidth automatically vary over time with :cpp:func:`simgrid::s4u::Link::set_bandwidth_profile` (C++) or :py:func:`simgrid.Link.set_bandwidth_profile` (python).
+
+Once implemented, you will notice that slow communications may still result in situations
+where one worker only works at a given point of time. To overcome that, your master needs
+to send data to several workers in parallel, using
+:cpp:func:`simgrid::s4u::Mailbox::put_async` (C++) or :py:func:`simgrid.Mailbox.put_async` (Python)
+to start several communications in parallel, and
+:cpp:func:`simgrid::s4u::Comm::wait_any` (C++) or and :py:func:`simgrid.Comm.wait_any` (Python)
+to react to the completion of one of these communications. Actually, since this code somewhat tricky
+to write, it's provided as :ref:`an example <s4u_ex_communication>` in the distribution (search for
+``wait_any`` in that page).
+
+Dealing with failures
+.....................
+
+Turn a given link off with :cpp:func:`simgrid::s4u::Link::turn_off` (C++) or :py:func:`simgrid.Link.turn_off` (python).
+You can even implement churn where a link automatically turn off and on again over time with :cpp:func:`simgrid::s4u::Link::set_state_profile` (C++) or :py:func:`simgrid.Link.set_state_profile` (python).
+
+If a link fails while you try to use it, ``wait()`` will raise a ``NetworkFailureException`` that you need to catch.
+Again, there is a nice example demoing this feature, :ref:`under platform-failures <s4u_ex_communication>`.
+
+Lab 5: Competing Applications
-----------------------------
-It is now time to start several applications at once, with the following ``deployment4.xml`` file.
+.. rst-class:: learning-goals
+
+ **Learning goals:**
-.. literalinclude:: tuto_s4u/deployment4.xml
+ * Advanced vizualization through tracing categories
+
+
+It is now time to start several applications at once, with the following ``deployment5.xml`` file.
+
+.. literalinclude:: tuto_s4u/deployment5.xml
:language: xml
Things happen when you do so, but it remains utterly difficult to
-understand what's happening exactely. Even Gantt visualizations
+understand what's happening exactly. Even Gantt visualizations
contain too much information to be useful: it is impossible to
-understand which task belong to which application. To fix this, we
+understand which task belongs to which application. To fix this, we
will categorize the tasks.
Instead of starting the execution in one function call only with
``this_actor::execute(cost)``, you need to
-create the execution activity, set its tracing category, and then start
-it and wait for its completion, as follows:
+create the execution activity, set its tracing category, start it
+and wait for its completion, as follows.
+
+.. tabs::
+
+ .. group-tab:: C++
+
+ Use :cpp:func:`simgrid::s4u::Exec::set_tracing_category` to change the category of an execution.
+
+ .. code-block:: cpp
-.. code-block:: cpp
+ simgrid::s4u::ExecPtr exec = simgrid::s4u::this_actor::exec_init(compute_cost);
+ exec->set_tracing_category(category);
+ // exec->start() is optional here as wait() starts the activity on need
+ exec->wait();
- simgrid::s4u::ExecPtr exec = simgrid::s4u::this_actor::exec_init(compute_cost);
- exec->set_tracing_category(category);
- // exec->start() is optional here as wait() starts the activity on need
- exec->wait();
+ You can shorten this code as follows:
-You can make the same code shorter as follows:
+ .. code-block:: cpp
-.. code-block:: cpp
+ simgrid::s4u::this_actor::exec_init(compute_cost)->set_tracing_category(category)->wait();
+
+ .. group-tab:: Python
+
+ Use :py:func:`simgrid.Exec.set_tracing_category` to change the category of an execution.
+
+ .. code-block:: python
+
+ exec = simgrid:.this_actor.exec_init(compute_cost)
+ exec.set_tracing_category(category)
+ // exec.start() is optional here as wait() starts the activity on need
+ exec->wait()
+
+ You can shorten this code as follows:
+
+ .. code-block:: python
+
+ simgrid.this_actor.exec_init(compute_cost).set_tracing_category(category).wait()
- simgrid::s4u::this_actor::exec_init(compute_cost)->set_tracing_category(category)->wait();
Visualizing the result
.......................
Include here the minimal setting to view something in R.
-
-Lab 5: Better Scheduling
-------------------------
-
-You don't need a very advanced visualization solution to notice that
-round-robin is completely suboptimal: most of the workers keep waiting
-for more work. We will move to a First-Come First-Served mechanism
-instead.
-
-For that, your workers should explicitly request for work with a
-message sent to a channel that is specific to their master. The name
-of that private channel can be the one used to categorize the
-executions, as it is already specific to each master.
-
-The master should serve in a round-robin manner the requests it
-receives, until the time is up. Changing the communication schema can
-be a bit hairy, but once it works, you will see that such as simple
-FCFS schema allows one to double the amount of tasks handled over time
-here. Things may be different with another platform file.
-
Further Improvements
-....................
+--------------------
From this, many things can easily be added. For example, you could:
-- Allow workers to have several pending requests so as to overlap
+- Allow workers to have several pending requests to overlap
communication and computations as much as possible. Non-blocking
communication will probably become handy here.
- Add a performance measurement mechanism, enabling the master to make smart scheduling choices.
What is the largest number of tasks requiring 50e6 flops and 1e5
bytes that you manage to distribute and process in one hour on
``g5k.xml`` ?
-- Optimize not only for the amount of tasks handled, but also for the
- total energy dissipated.
-- And so on. If you come up with a really nice extension, please share
+- Optimize not only for the number of tasks handled but also for the total energy dissipated.
+- And so on. If you come up with a nice extension, please share
it with us so that we can extend this tutorial.
After this Tutorial
-------------------
-This tutorial is now terminated. You could keep reading the [online documentation][fn:4] or
-[tutorials][fn:7], or you could head up to the example section to read some code.
+This tutorial is now terminated. You could keep reading the online documentation and
+tutorials, or you could head up to the :ref:`example section <s4u_examples>` to read some code.
.. todo::
Things to improve in the future:
- - Propose equivalent exercises and skeleton in java (and Python once we have a python binding).
+ - Propose equivalent exercises and skeleton in Java once we fix the Java binding.
+
+.. |br| raw:: html
+
+ <br />
.. LocalWords: SimGrid
