.. _intro_concepts:
-Main Concepts
-=============
-
+Introduction
+============
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-Introduction
-============
+Main Concepts
+-------------
Typical Study based on SimGrid
-------------------------------
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Any SimGrid study entails the following components:
- - The studied **Application**. This can be either a distributed
- algorithm described in our simple APIs, or a full featured real
+ - The studied **application**. This can be either a distributed
+ algorithm described in our simple APIs or a full-featured real
parallel application using for example the MPI interface
:ref:`(more info) <application>`.
- - The **Simulated Platform**. This is a description of a given
+ - The **simulated platform**. This is a description of a given
distributed system (machines, links, disks, clusters, etc). Most of
- the platform files are written in XML although a Lua interface is
- under development. SimGrid makes it easy to augment the Simulated
- Platform with a Dynamic Scenario where for example the links are
- slowed down (because of external usage) or the machines fail. You
- even have support to specify the applicative workload that you want
- to feed to your application
+ the platform files are written in XML but a new C++ programmatic
+ interface has recently been introduced. SimGrid makes it easy to
+ augment the Simulated Platform with a Dynamic Scenario where for
+ example the links are slowed down (because of external usage) or the
+ machines fail. You even have support to specify the applicative
+ workload that you want to feed to your application
:ref:`(more info) <platform>`.
- - The application's **Deployment Description**. In SimGrid
+ - The application's **deployment description**. In SimGrid
terminology, the application is an inert set of source files and
binaries. To make it run, you have to describe how your application
should be deployed on the simulated platform. You need to specify
which process is mapped onto which machine, along with their parameters
:ref:`(more info) <scenario>`.
- - The **Platform Models**. They describe how the simulated platform
+ - The **platform models**. They describe how the simulated platform
reacts to the actions of the application. For example, they compute
the time taken by a given communication on the simulated platform.
These models are already included in SimGrid, and you only need to
:ref:`(more info) <models>`.
These components are put together to run a **simulation**, that is an
-experiment or a probe. The result of one or many simulation provides
-an **outcome** (logs, visualization, or statistical analysis) that help
-answering the **question** targeted by this study.
+experiment or a probe. Simulations produce **outcomes** (logs,
+visualization, or statistical analysis) that help to answer the
+**question** targeted by this study.
Here are some questions on which SimGrid is particularly relevant:
- **Design the best [Simulated] Platform for a given Application.**
Tweaking the platform file is much easier than building a new real
- platform for testing purpose. SimGrid also allows for the co-design
+ platform for testing purposes. SimGrid also allows for the co-design
of the platform and the application by modifying both of them.
- **Debug Real Applications**. With real systems, is sometimes
less important, but you should pay close attention if you want to be
confident in the results coming out of your simulations. In
particular, you should not blindly trust your results but always
-strive to double-check them. Likewise, you should question the realism
-of your input configuration, and we even encourage you to doubt (and
-check) the provided performance models.
+strive to double-check them. Likewise, :ref:`you should question the
+realism of your input configuration <howto_calibration>`, and we even
+encourage you to :ref:`doubt (and check) the provided performance models
+<howto_science>`.
To ease such questioning, you really should logically separate these
parts in your experimental setup. It is seen as a very bad practice to
-merge the application, the platform, and the deployment all together.
+merge the application, the platform, and the deployment altogether.
SimGrid is versatile and your mileage may vary, but you should start
with your Application specified as a C++ or Java program, using one of
-the provided XML platform file, and with your deployment in a separate
+the provided XML platform files, and with your deployment in a separate
XML file.
SimGrid Execution Modes
------------------------
+^^^^^^^^^^^^^^^^^^^^^^^
Depending on the intended study, SimGrid can be run in several execution modes.
possible platforms that you could imagine (and more).
You just provide the application and its deployment (number of
-processes and parameters), and the model checker will literally
+processes and parameters), and the model checker will
explore all possible outcomes by testing all possible message
interleavings: if at some point a given process can either receive the
message A first or the message B depending on the platform
scenario where B arrives first.
This is a very powerful mode, where you can evaluate the correctness of
-your application. It can verify either **safety properties** (asserts)
+your application. It can verify either **safety properties** (assertions)
or **liveness properties** stating for example that if a given event
occurs, then another given event will occur in a finite amount of
steps. This mode is not only usable with the abstract algorithms
A classical trap is that the Model Checker can only verify whether
your application fits the properties provided, which is useless if you
have a bug in your property. Remember also that one way for your
-application to never violate a given assert is to not start at all,
+application to never violate a given assertion is to not start at all,
because of a stupid bug.
Another limit of this mode is that it does not use the performance
models of the simulation mode. Time becomes discrete: You can say for
example that the application took 42 steps to run, but there is no way
-to know how much time it took or the amount of watts that were dissipated.
+to know how much time it took or the number of watts that were dissipated.
Finally, the model checker only explores the interleavings of
computations and communications. Other factors such as thread
the actual hosting machine to benchmark it.
SimGrid Limits
---------------
+^^^^^^^^^^^^^^
-This framework is by no means the holly grail, able to solve
+This framework is by no means the holy grail, able to solve
every problem on Earth.
**SimGrid scope is limited to distributed systems.** Real-time
multi-threaded systems are out of this scope. You could probably tweak
-SimGrid for such studies (or the framework could possibly be extended
+SimGrid for such studies (or the framework could be extended
in this direction), but another framework specifically targeting such a
use case would probably be more suited.
-**There is currently no support for wireless networks**.
+**There is currently no support for 5G or LoRa networks**.
The framework could certainly be improved in this direction, but this
still has to be done.
malicious agents.
SimGrid Success Stories
------------------------
+^^^^^^^^^^^^^^^^^^^^^^^
-SimGrid was cited in over 1,500 scientific papers (according to Google
-Scholar). Among them
-`over 200 publications <https://simgrid.org/Usages.html>`_
-(written by about 300 individuals) use SimGrid as a scientific
+SimGrid was cited in over 3,000 scientific papers (according to Google
+Scholar). Among them,
+`over 500 publications <https://simgrid.org/usages.html>`_
+(written by hundreds of individuals) use SimGrid as a scientific
instrument to conduct their experimental evaluation. These
numbers do not include the articles contributing to SimGrid.
This instrument was used in many research communities, such as
`Network Architecture <http://dx.doi.org/10.1109/TPDS.2016.2613043>`_,
`Fog Computing <http://ieeexplore.ieee.org/document/7946412/>`_, or
`Batch Scheduling <https://hal.archives-ouvertes.fr/hal-01333471>`_
-`(more info) <https://simgrid.org/Usages.html>`_.
+`(more info) <https://simgrid.org/usages.html>`_.
If your platform description is accurate enough (see
`here <http://hal.inria.fr/hal-00907887>`_ or
computing the electronic structure of chemical elements developed by
the CEA), `StarPU <http://starpu.gforge.inria.fr/>`_ (a
Unified Runtime System for Heterogeneous Multicore Architectures
-developed by Inria Bordeaux) and
-`TomP2P <https://tomp2p.net/dev/simgrid/>`_ (a high performance
+developed by Inria Bordeaux), and
+`TomP2P <https://tomp2p.net/dev/simgrid/>`_ (a high-performance
key-value pair storage library developed at the University of Zurich).
Some of these applications enjoy large user communities themselves.
.. LocalWords: SimGrid
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