are its limitations. Then you definitely should read the \ref
MSG_examples. There is also a mailing list: <simgrid-user@lists.gforge.inria.fr>.
+\subsection faq_interfaces What is the difference between MSG, SimDag, and GRAS? Do they serve the same purpose?
+
+It depend on how you define "purpose", I guess ;)
+
+They all allow you to build a prototype of application which you can run
+within the simulator afterward. They all share the same simulation kernel,
+which is the core of the SimGrid project. They differ by the way you express
+your application.
+
+With SimDag, you express your code as a collection of interdependent
+parallel tasks. So, in this model, applications can be seen as a DAG of
+tasks.
+
+With both GRAS and MSG, your application is seen as a set of communicating
+processes, exchanging data by the way of messages and performing computation
+on their own.
+
+The difference between both is that MSG is somehow easier to use, but GRAS
+is not limitated to the simulator. Once you're done writing your GRAS code,
+you can run your code both in the simulator or on a real platform. For this,
+there is two implementations of the GRAS interface, one for simulation, one
+for real execution. So, you just have to relink your code to chose one of
+both world.
+
\subsection faq_generic Building a generic simulator
Please read carefully the \ref MSG_examples. You'll find in \ref
communications have an influence on computational power. Should it be taken
into account too?
-So, we decided not to include such a function into MSG and let people do it
-thereselves so that they get the value matching exactly what they mean. One
-possibility is to run active measurement as in next code snippet. It is very
-close from what you would have to do out of the simulator, and thus gives
-you information that you could also get in real settings to not hinder the
-realism of your simulation.
+First of all, it's near to impossible to predict the load beforehands in the
+simulator since it depends on too much parameters (background load
+variation, bandwidth sharing algorithmic complexity) some of them even being
+not known beforehands (other task starting at the same time). So, getting
+this information is really hard (just like in real life). It's not just that
+we want MSG to be as painful as real life. But as it is in some way
+realistic, we face some of the same problems as we would face in real life.
+
+How would you do it for real? The most common option is to use something
+like NWS that performs active probes. The best solution is probably to do
+the same within MSG, as in next code snippet. It is very close from what you
+would have to do out of the simulator, and thus gives you information that
+you could also get in real settings to not hinder the realism of your
+simulation.
\verbatim
double get_host_load() {
20.0 0.9
\endverbatim
-At time 0, our CPU will deliver 100 Mflop/s. At time 11.0, it will
-deliver only 50 Mflop/s until time 20.0 where it will will start
-delivering 90 Mflop/s. Last at time 21.0 (20.0 plus the periodicity
-1.0), we'll be back to the beginning and it will deliver 100Mflop/s.
+At time 0, our CPU will deliver 100 flop/s. At time 11.0, it will
+deliver only 50 flop/s until time 20.0 where it will will start
+delivering 90 flop/s. Last at time 21.0 (20.0 plus the periodicity
+1.0), we'll be back to the beginning and it will deliver 100 flop/s.
Now let's look at the state file:
\verbatim
You have at your disposal the following options: bandwidth_file,
latency_file and state_file. The only difference with CPUs is that
bandwidth_file and latency_file do not express fraction of available
-power but are expressed directly in Mb/s and seconds.
+power but are expressed directly in bytes per seconds and seconds.
\subsection faq_flexml_bypassing How can I have some C functions do what the platform file does?
the development of FleXML, I can grant you that any patches would be really
welcome and quickly integrated.
+<b>Update:</b> A new version of FleXML (1.7) was released. Most of the work
+was done by William Dowling, who use it in his own work. The good point is
+that it now use a dynamic buffer, and that the memory usage was greatly
+improved. The downside is that William also changed some things internally,
+and it breaks the hack we devised to bypass the parser, as explained in
+\ref faq_flexml_bypassing. Indeed, this is not a classical usage of the
+parser, and Will didn't imagine that we may have used (and even documented)
+such a crude usage of FleXML. So, we now have to repare the bypassing
+functionnality to use the lastest FleXML version and fix the memory usage in
+SimGrid.
+
\subsection faq_gras_transport GRAS spits networking error messages
Gras, on real platforms, naturally use regular sockets to communicate. They
