/*! \page faq Frequently Asked Questions
-\author Arnaud Legrand <arnaud.legrand#imag.fr>
-
\section faq_installation Installing the SimGrid library
Many people have been asking me questions on how to use SimGrid. Quite
\section faq_simgrid I'm new to SimGrid. I have some questions. Where should I start ?
-You are at the right place... Having a look to these <a
-href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">slides</a>
+You are at the right place... Having a look to these
+<a href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">slides</a>
may give you some insights on what SimGrid can help you to do and what
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_platform Building a realistic platform
I can speak more than an hour on this subject and I still do not have
-the right answer, just some ideas. You can read the following <a
-href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">slides</a>.
+the right answer, just some ideas. You can read the following
+<a href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">slides</a>.
It may give you some hints. You can also have a look at the
<tt>tools/platform_generation/</tt> directory. There is a perl-script
I use to annotate a Tiers generated platform (may not be up-to-date
to gforge so people that are interested by helping on this part will
have the possibility to do it.
-\subsection But I wanted to implement a distributed dynamic scheduler of DAGs... How can I do that it SG is not available anymore in the next versions ?
+\subsection faq_SG_DAG But I wanted to implement a distributed dynamic scheduler of DAGs... How can I do that it SG is not available anymore in the next versions ?
Distributed is somehow "contagious". If you start making distributed
decisions, there is no way to handle DAGs directly anymore (unless I am
Note however that SURF will be slower than the old SG to handle traces with
a lots of variations (there is no trace integration anymore).
+\section faq_flexml_limit I get the message "surf_parse_lex: Assertion `next<limit' failed."
+
+This is because your platform file is too big for the parser.
+
+Actually, the message comes directly from FleXML, the technology on top of
+which the parser is built. FleXML has the bad idea of fetching the whole
+document in memory before parsing it. And moreover, the memory buffer size
+must be determinded at compilation time.
+
+We use a value which seems big enough for our need withour bloating the
+simulators footprints. But of course your mileage may vary. In this case,
+just edit src/surf/surfxml.l modify the definition of
+FLEXML_BUFFERSTACKSIZE. E.g.
+
+\verbatim
+#define FLEXML_BUFFERSTACKSIZE 1000000000
+\endverbatim
+
+Then recompile and everything should be fine, provided that your version of
+Flex is recent enough (>= 2.5.31). If not the compilation process should
+warn you.
+
+A while ago, we worked on FleXML to reduce a bit its memory consumtion, but
+these issues remain. There is two things we should do:
+
+ - use a dynamic buffer instead of a static one so that the only limit
+ becomes your memory, not a stupid constant fixed at compilation time
+ (maybe not so difficult).
+ - change the parser so that it does not need to get the whole file in
+ memory before parsing
+ (seems quite difficult, but I'm a complete newbe wrt flex stuff).
+
+These are changes to FleXML itself, not SimGrid. But since we kinda hijacked
+the development of FleXML, I can grant you that any patches would be really
+welcome and quickly integrated.
+
+\section faq_host_load Where is the get_host_load function hidden in MSG?
+
+There is no such thing because its semantic wouldn't be really clear. Of
+course, it is something about the amount of host throughput, but there is as
+many definition of "host load" as people asking for this function.
+
+It may be instantaneous value or an average one. Moreover it may be only the
+power of the computer, or may take the background load into account, or may
+even take the currently running tasks into account. In some SURF models,
+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.
+
+\verbatim
+double get_host_load() {
+ m_task_t task = MSG_task_create("test", 0.001, 0, NULL);
+ double date = MSG_get_clock();
+
+ MSG_task_execute(task);
+ date = MSG_get_clock() - date;
+ MSG_task_destroy(task);
+ return (0.001/date);
+}
+\endverbatim
+
+Of course, it may not match your personal definition of "host load". In this
+case, please detail what you mean on the mailing list, and we will extend
+this FAQ section to fit your taste if possible.
+
+
+
+\author Arnaud Legrand (arnaud.legran::imag.fr)
+\author Martin Quinson (martin.quinson::loria.fr)
+
+
*/
+
