What is SimGrid
===============
-SimGrid is a framework to simulate distributed computer systems.
+SimGrid is a framework to simulate distributed computer systems.
-It can be used to either assess abstract algorithms, or to profile and
+It can be used to either assess abstract algorithms or to profile and
debug real distributed applications. SimGrid enables studies in the
domains of (data-)Grids, IaaS Clouds, Clusters, High Performance
-Computing, Volunteer Computing and Peer-to-Peer systems.
+Computing, Volunteer Computing, and Peer-to-Peer systems.
Technically speaking, SimGrid is a library. It is neither a graphical
interface nor a command-line simulator running user scripts. The
interaction with SimGrid is done by writing programs with the exposed
functions to build your own simulator.
-SimGrid is a Free Software distributed under the LGPL license. You are
-thus welcome to use it as you wish, or even to modify and distribute
+SimGrid is a Free Software distributed under the LGPLv3 license. You are
+thus welcome to use it as you wish or even to modify and distribute
your version (provided that your version is as free as ours). It also
means that SimGrid is developed by a vivid community of users and
developers. We hope that you will come and join us!
SimGrid is the result of almost 20 years of research from several
-groups, both in France and in the USA. It benefited of many funding
-from various research instances, including the ANR, Inria, CNRS,
-University of Lorraine, University of Hawai'i at Manoa, ENS Rennes and
+groups, both in France and in the U.S.A. It benefited of many funding
+from various research bodies, including the ANR, Inria, CNRS,
+University of Lorraine, University of Hawai'i at Manoa, ENS Rennes, and
many others. Many thanks to our generous sponsors!
SimGrid is a powerful tool, but its learning curve can be rather
- 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
+ parallel application using for example the MPI interface
:ref:`(more info) <application>`.
- The **Virtual Platform**. This is a description of a given
the platform files are written in XML althrough a Lua interface is
under development. SimGrid makes it easy to augment the Virtual
Platform with a Dynamic Scenario where for example the links are
- slowed down (because of external usage), the machines fail. You
+ slowed down (because of external usage) or the machines fail. You
have even support to specify the applicative workload that you want
to feed to your application
:ref:`(more info) <platform>`.
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 virtual platform. You need to specify
- which process is mapped on which host, along with their parameters
+ which process is mapped on which machine, along with their parameters
:ref:`(more info) <scenario>`.
- The **Platform Models**. They describe how the virtual platform
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, statistical analysis) that help
+an **outcome** (logs, visualization, or statistical analysis) that help
answering the **question** targeted by this study.
Here are some questions on which SimGrid is particularly relevant:
- **Compare an Application to another**. This is the classical use
case for scientists, who use SimGrid to test how the solution that
- they contribute compares to the existing solutions from the
+ they contribute to compares to the existing solutions from the
literature.
- **Design the best Virtual Platform for a given Application.**
Tweaking the platform file is much easier than building a new real
- platform for testing purpose. SimGrid also allows co-design of the
- platform and the application by modifying both of them.
+ platform for testing purpose. 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
difficult to reproduce the exact run leading to the bug that you
Depending on the context, you may see some parts of this process as
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 trust blindly your results but always
+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.
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 all together.
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
In this mode, SimGrid can provide information about the time taken by
your application, the amount of energy dissipated by the platform to
-run your application and the detailed usage of each resource.
+run your application, and the detailed usage of each resource.
**Model-Checking Mode**. This can be seen as a sort of exhaustive
testing mode, where every possible outcome of your application is
scenario where B arrives first.
This is a very powerful mode, where you can evaluate the correction of
-your application. It can verify either **safety properties** (asserts)
+your application. It can verify either **safety properties** (asserts)
or **liveless 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
developed on top of the SimGrid APIs, but also with real MPI
-applications (to some extend).
+applications (to some extent).
The main limit of Model Checking lays in the huge amount of scenarios
to explore. SimGrid tries to explore only non-redundant scenarios
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 the amount of seconds that it took or the amount of watts that
-it dissipated.
+to know how much time it took or the amount of watts that were dissipated.
Finally, the model checker only explores the interleavings of
computations and communications. Other factors such as thread
tool.
**Benchmark Recording Mode**. During debug sessions, continuous
-integration testing and other similar use cases, you are often only
+integration testing, and other similar use cases, you are often only
interested in the control flow. If your application apply filters to
huge images split in small blocks, the filtered image is probably not
what you are interested in. You are probably looking for a way to run
--------------
This framework is by no means the perfect holly grail able to solve
-every problem on earth.
+every problem on earth.
**SimGrid scope is limited to distributed systems.** Real-time
-multi-threaded systems are not in the scope. You could probably tweak
+multi-threaded systems are out of scope. You could probably tweak
SimGrid for such studies (or the framework could possibly be extended
-in this direction), but another framework specifically targeting this
+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 wireless networks**.
The framework could certainly be improved in this direction, but this
-is still to be done.
+still has to be done.
**There is no perfect model, only models adapted to your study.**
-The SimGrid models target fast, large studies yet requesting a
+The SimGrid models target fast and large studies yet requesting
realistic results. In particular, our models abstract away parameters
-and phenomenon that are often irrelevant to the realism in our
-context.
+and phenomena that are often irrelevant to the realism in our
+context.
SimGrid is simply not intended to any study that would mandate the
abstracted phenomenon. Here are some **studies that you should not do
with SimGrid**:
- - Studying the effect of L3 vs L2 cache effects on your application
+ - Studying the effect of L3 vs. L2 cache effects on your application
- Comparing kernel schedulers and policies
- Comparing variants of TCP
- Exploring pathological cases where TCP breaks down, resulting in
Scholar). Among them
`over 200 publications <https://simgrid.org/Usages.html>`_
(written by about 300 individuals) use SimGrid as a scientific
-instrument to conduct their experimental evaluation. These
-numbers do not count the articles contributing to SimGrid.
-This instrument was used in many research communities, such as
+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
`High-Performance Computing <https://hal.inria.fr/inria-00580599/>`_,
`Cloud Computing <http://dx.doi.org/10.1109/CLOUD.2015.125>`_,
`Workflow Scheduling <http://dl.acm.org/citation.cfm?id=2310096.2310195>`_,
`here <http://hal.inria.fr/hal-00907887>`_ or
`there <https://hal.inria.fr/hal-01523608>`_),
SimGrid can provide high-quality performance predictions. For example,
-we determined the speedup achieved by the Tibidabo Arm-based
+we determined the speedup achieved by the Tibidabo ARM-based
cluster before its construction
-(`paper <http://hal.inria.fr/hal-00919507>`_). In this case,
+(`paper <http://hal.inria.fr/hal-00919507>`_). In this case,
some differences between the prediction and the real timings were due to
-misconfiguration or other problems with the real platforms. To some extent,
+misconfiguration or other problems with the real platform. To some extent,
SimGrid could even be used to debug the real platform :)
-SimGrid is also used to debug, improve and tune several large
+SimGrid is also used to debug, improve, and tune several large
applications.
`BigDFT <http://bigdft.org>`_ (a massively parallel code
computing the electronic structure of chemical elements developped by
