\htmlinclude .FAQ.doc.toc
+\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/slides_g5k_simul.pdf">slides</a>
+(or to these
+<a href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">"obsolete" 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_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 First steps with SimGrid
+
+If you decide to go for the MSG interface, please read carefully the
+\ref MSG_examples. You'll find in \ref MSG_ex_master_slave a very
+simple consisting of a master (that owns a bunch of tasks and
+distributes them) , some slaves (that process tasks whenever they
+receive one) and some forwarder agents (that simply pass the tasks
+they receive to some slaves).
+
+If you decide to go for the GRAS interface, you should definitively
+read the \ref GRAS_tut. The first section constitutes an introduction
+to the tool and presents the model we use. The second section
+constitutes a complete step-by-step tutorial building a distributed
+application from the begining and exemplifying most of the GRAS
+features in the process. The last section groups some HOWTOS
+highlighting a given feature of the framework in a more concise way.
+
+If you decide to go for another interface, I'm afraid your only sources
+of information will be the source code and the mailing lists...
+
+\subsection faq_visualization Visualizing and analyzing the results
+
+It is sometime convenient to "see" how the agents are behaving. If you
+like colors, you can use <tt>tools/MSG_visualization/colorize.pl </tt>
+as a filter to your MSG outputs. It works directly with INFO. Beware,
+INFO() prints on stderr. Do not forget to redirect if you want to
+filter (e.g. with bash):
+\verbatim
+./msg_test small_platform.xml small_deployment.xml 2>&1 | ../../tools/MSG_visualization/colorize.pl
+\endverbatim
+
+We also have a more graphical output. Have a look at MSG_paje_output(). It
+generates an input to <a href="http://www-id.imag.fr/Logiciels/paje/">Paje</a>.
+<center>
+\htmlonly
+ <a href="Paje_MSG_screenshot.jpg"><img src="Paje_MSG_screenshot_thn.jpg"></a>
+\endhtmlonly
+</center>
+
+Vizualization with Paje can be seen as a kind of postmortem
+analysis. However, as soon as you start playing with big simulations,
+you'll realize that processing such output is kind of tricky. There is
+so much generic informations that it is hard to find the information
+you are looking for.
+
+As a matter of fact, loging really depends on simulations (e.g. what
+kind of events is important...). That is why we do not propose a big
+dump of your whole simulation (it would slow everything down) but give
+you neat tools to structure you logs. Have a look at \ref XBT_log. In
+fact, rather than a post-mortem analysis, you may want to do it on the
+fly. The process you are running can do whatever you want. Have you
+thought about adding a global structure where you directly compute the
+informations that are really important rather than writing everything
+down and then processing huge files?
+
+\subsection faq_C Argh! Do I really have to code in C?
+
+Up until now, there is no binding for other languages. If you use C++,
+you should be able to use the SimGrid library as a standard C library
+and everything should work fine (simply <i>link</i> against this
+library; recompiling SimGrid with a C++ compiler won't work and it
+wouldn't help if you could).
+
+In fact, we are currently working on Java bindings of MSG to allow
+all the undergrad students of the world to use this tool. This is a
+little more tricky than I would have expected, but the work is moving
+fast forward [2006/05/13]. More languages are evaluated, but for now,
+we do not feel a real demand for any other language. Please speak up!
+
\section faq_installation Installing the SimGrid library
Many people have been asking me questions on how to use SimGrid. Quite
\endverbatim
If at some point, something fails, check the section "\ref
-faq_compil_trouble". If it does not help, you can report this problem to the
+faq_trouble_compil". If it does not help, you can report this problem to the
list but, please, avoid sending a laconic mail like "There is a problem. Is it
okay?". Send the config.log file which is automatically generated by
configure. Try to capture both the standard output and the error output of the
instructions of Section \ref faq_compiling.
We insist on the fact that you really need the latest versions of
-autoconf and automake. Doing this step on exotic architectures/systems
+autoconf, automake and libtool. Doing this step on exotic architectures/systems
(i.e. anything different from a recent linux distribution) may be
-... uncertain. If you want to use the CVS version on another
-architecture/system, you should do the previous steps on a perfectly
-standard box, then do a <tt>make dist</tt> that will build you a
-perfectly portable SimGrid archive.
+... uncertain. If you need to compile the CVS version on a machine where all these
+dependencies are not met, the easiest is to do <tt>make dist</tt> in the CVS
+dir of another machine where all dependencies are met. It will create an
+archive you may deploy on other sites just as a regular stable release.
In summary, the following commands will checkout the CVS, regenerate the
-configure script and friends, configure SimGrid and build an archive you can
-use on another machine afterward.
+configure script and friends, configure SimGrid and build it.
\verbatim cvs -d :pserver:anonymous@scm.gforge.inria.fr:/cvsroot/simgrid login
cvs -d :pserver:anonymous@scm.gforge.inria.fr:/cvsroot/simgrid checkout simgrid
cd simgrid
./bootstrap
-./configure --enable-maintainer-mode
-make dist \endverbatim
+./configure --enable-maintainer-mode --prefix=<where to install SimGrid>
+make \endverbatim
+
+Then, if you want to install SimGrid on the current box, just do:
+\verbatim make install \endverbatim
+
+If you want to build an snapshot of the CVS to deploy it on another box (for
+example because the other machine don't have the autotools), do:
+\verbatim make dist \endverbatim
+
+Moreover, you should never call the autotools manually since you must run
+them in a specific order with specific arguments. Most of the times, the
+makefiles will automatically call the tools for you. When it's not possible
+(such as the first time you checkout the CVS), use the ./bootstrap command
+to call them explicitely.
+
\subsection faq_setting_MSG Setting up your own MSG code
Program (cross-)compiled with mingw32 do request an extra DLL at run-time to be
usable. For example, if you want to test your build with wine, you should do
the following to put this library where wine looks for DLLs.
-\verbatim cp /usr/share/doc/mingw32-runtime/mingwm10.dll.gz ~/.wine/c/windows/system/
+\verbatim
+cp /usr/share/doc/mingw32-runtime/mingwm10.dll.gz ~/.wine/c/windows/system/
gunzip ~/.wine/c/windows/system/mingwm10.dll.gz
\endverbatim
-The DLL is builded in src/.libs, and installed in the <prefix>/bin directory
+The DLL is builded in src/.libs, and installed in the <i>prefix</i>/bin directory
when you run make install.
If you want to use it in a native project on windows, you need to use
header files with tons of __declspec(dllexport) cruft. We only need to do so
for data, but there is no public data in SimGrid so we are good.
-\section faq_simgrid I'm new to SimGrid. I have some questions. Where should I start?
+\section faq_howto Feature related questions
-You are at the right place... Having a look to these
-<a href="http://graal.ens-lyon.fr/~alegrand/articles/slides_g5k_simul.pdf">slides</a>
-(or to these
-<a href="http://graal.ens-lyon.fr/~alegrand/articles/Simgrid-Introduction.pdf">"obsolete" 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_generic Building a generic simulator
-
-Please read carefully the \ref MSG_examples. You'll find in \ref
-MSG_ex_master_slave a very simple consisting of a master (that owns a bunch of
-tasks and distributes them) , some slaves (that process tasks whenever
-they receive one) and some forwarder agents (that simply pass the
-tasks they receive to some slaves).
-
-\subsection faq_visualization Visualizing the schedule
-
-It is sometime convenient to "see" how the agents are behaving. If you
-like colors, you can use <tt>tools/MSG_visualization/colorize.pl </tt>
-as a filter to your MSG outputs. It works directly with INFO. Beware,
-INFO() prints on stderr. Do not forget to redirect if you want to
-filter (e.g. with bash):
-\verbatim
-./msg_test small_platform.xml small_deployment.xml 2>&1 | ../../tools/MSG_visualization/colorize.pl
-\endverbatim
-
-We also have a more graphical output. Have a look at MSG_paje_output(). It
-generates an input to <a href="http://www-id.imag.fr/Logiciels/paje/">Paje</a>.
-<center>
-\htmlonly
- <a href="Paje_MSG_screenshot.jpg"><img src="Paje_MSG_screenshot_thn.jpg"></a>
-\endhtmlonly
-</center>
-
-\subsection faq_postmortem_analysis Online/postmortem analysis
-
-Vizualization with Paje can be seen as a kind of postmortem
-analysis. However, as soon as you start playing with big simulations,
-you'll realize that processing such output is kind of tricky. There is
-so much generic informations that it is hard to find the information
-you are looking for.
-
-As a matter of fact, loging really depends on simulations (e.g. what
-kind of events is important...). That is why we do not propose a big
-dump of your whole simulation (it would slow everything down) but give
-you neat tools to structure you logs. Have a look at \ref XBT_log. In
-fact, rather than a post-mortem analysis, you may want to do it on the
-fly. The process you are running can do whatever you want. Have you
-thought about adding a global structure where you directly compute the
-informations that are really important rather than writing everything
-down and then processing huge files ?
-
-\subsection faq_C Argh! Do I really have to code in C ?
-
-Up until now, there is no binding for other languages. If you use C++,
-you should be able to use the SimGrid library as a standard C library
-and everything should work fine (simply <i>link</i> against this
-library; recompiling SimGrid with a C++ compiler won't work and it
-wouldn't help if you could).
-
-In fact, the bindings needed to allow one to use SimGrid from Perl,
-Python, Java, etc. are double-layered. The first layer would allow
-you to call for example the MSG_task_get_name(task) function while
-what you really want is a proper object wrapping allowing you to call
-task->name(). That's the purpose of the second layer. The first one
-is granted with C++ but can be done with tools like
-<a href="www.swig.org/">swig</a> for other languages like Perl, Ruby,
-Python, CAML. None of us really need the second one (which is a bit
-more demanding and cannot be automatically generated) yet and there is
-no real point in doing the first one without the second. :)
-
-As usual, you're welcome to participate.
-
-\section faq_MIA How to ....? Is there a function in the API to simply ....?
+\subsection faq_MIA "Could you please add (your favorite feature here) to SimGrid?"
Here is the deal. The whole SimGrid project (MSG, SURF, GRAS, ...) is
meant to be kept as simple and generic as possible. We cannot add
functions for everybody's need when these functions can easily be
built from the ones already in the API. Most of the time, it is
possible and when it was not possible we always have upgraded the API
-accordingly. When somebody asks us a question like "How to do that ?
-Is there a function in the API to simply do this ?", we're always glad
+accordingly. When somebody asks us a question like "How to do that?
+Is there a function in the API to simply do this?", we're always glad
to answer and help. However if we don't need this code for our own
need, there is no chance we're going to write it... it's your job! :)
The counterpart to our answers is that once you come up with a neat
people have asked about it and we have given hints on how to simply do
it with MSG. Feel free to contribute...
-\subsection faq_MIA_examples I want some more complex examples!
+\subsection faq_MIA_MSG MSG features
+
+\subsubsection faq_MIA_examples I want some more complex MSG examples!
Many people have come to ask me a more complex example and each time,
they have realized afterward that the basics were in the previous three
us if something is not clear and once again feel free to participate!
:)
-\subsection faq_MIA_taskdup Missing in action: Task duplication/replication
+\subsubsection faq_MIA_taskdup Missing in action: MSG Task duplication/replication
There is no task duplication in MSG. When you create a task, you can
process it or send it somewhere else. As soon as a process has sent
You could use a dictionnary (#xbt_dict_t) of dynars (#xbt_dynar_t). If
you still don't see how to do it, please come back to us...
-\subsection faq_MIA_asynchronous I want to do asynchronous communications in MSG
+\subsubsection faq_MIA_asynchronous I want to do asynchronous communications in MSG
Up until now, there is no asynchronous communications in MSG. However,
you can create as many process as you want so you should be able to do
process only to handle communications may be problematic in term of
performance at some point). I'll add it in the distribution asap.
-\subsection faq_MIA_thread_synchronization I need to synchronize my MSG processes
+\subsubsection faq_MIA_thread_synchronization I need to synchronize my MSG processes
You obviously cannot use pthread_mutexes of pthread_conds. The best
thing would be to propose similar structures. Unfortunately, we
synchronization with fake communications (using MSG_task_get(),
MSG_task_put() and MSG_task_Iprobe()).
-\subsection faq_MIA_host_load Where is the get_host_load function hidden in MSG?
+\subsubsection faq_MIA_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,
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() {
case, please detail what you mean on the mailing list, and we will extend
this FAQ section to fit your taste if possible.
-\subsection faq_MIA_communication_time How can I get the *real* communication time ?
+\subsubsection faq_MIA_communication_time How can I get the *real* communication time?
Communications are synchronous and thus if you simply get the time
before and after a communication, you'll only get the transmission
}
\endverbatim
-\subsection faq_MIA_batch_scheduler Is there a native support for batch schedulers in SimGrid ?
-
-No, there is no native support for batch schedulers and none is
-planned because this is a very specific need (and doing it in a
-generic way is thus very hard). However some people have implemented
-their own batch schedulers. Vincent Garonne wrote one during his PhD
-and put his code in the contrib directory of our CVS so that other can
-keep working on it. You may find inspinring ideas in it.
+\subsection faq_MIA_SimDag SimDag related questions
-\subsection faq_MIA_checkpointing I need a checkpointing thing
-
-Actually, it depends on whether you want to checkpoint the simulation, or to
-simulate checkpoints.
-
-The first one could help if your simulation is a long standing process you
-want to keep running even on hardware issues. It could also help to
-<i>rewind</i> the simulation by jumping sometimes on an old checkpoint to
-cancel recent calculations.\n
-Unfortunately, such thing will probably never exist in SG. One would have to
-duplicate all data structures because doing a rewind at the simulator level
-is very very hard (not talking about the malloc free operations that might
-have been done in between). Instead, you may be interested in the Libckpt
-library (http://www.cs.utk.edu/~plank/plank/www/libckpt.html). This is the
-checkpointing solution used in the condor project, for example. It makes it
-easy to create checkpoints (at the OS level, creating something like core
-files), and rerunning them on need.
-
-If you want to simulate checkpoints instead, it means that you want the
-state of an executing task (in particular, the progress made towards
-completion) to be saved somewhere. So if a host (and the task executing on
-it) fails (cf. #MSG_HOST_FAILURE), then the task can be restarted
-from the last checkpoint.\n
-
-Actually, such a thing does not exists in SimGrid either, but it's just
-because we don't think it is fundamental and it may be done in the user code
-at relatively low cost. You could for example use a watcher that
-periodically get the remaining amount of things to do (using
-MSG_task_get_remaining_computation()), or fragment the task in smaller
-subtasks.
-
-\section faq_SG Where has SG disappeared?!?
+\subsubsection faq_SG Where has SG disappeared?
OK, it's time to explain what's happening to the SimGrid project. Let's
start with a little bit of history.
patterns. Some old codes using SG are currently under rewrite using
\ref SD_API to check that all needful functions are provided.
-\subsection faq_SG_DAG How to implement a distributed dynamic scheduler of DAGs.
+\subsubsection faq_SG_DAG How to implement a distributed dynamic scheduler of DAGs.
Distributed is somehow "contagious". If you start making distributed
decisions, there is no way to handle DAGs directly anymore (unless I
DAG is really the level of abstraction you want to work with, then you should
give a try to \ref SD_API.
-\section faq_dynamic Dynamic resources and platform building
+\subsection faq_MIA_generic Generic features
+
+\subsubsection faq_more_processes Increasing the amount of simulated processes
+
+Here are a few tricks you can apply if you want to increase the amount
+of processes in your simulations.
+
+ - <b>A few thousands of simulated processes</b> (soft tricks)\n
+ SimGrid can use either pthreads library or the UNIX98 contextes. On
+ most systems, the number of pthreads is limited and then your
+ simulation may be limited for a stupid reason. This is especially
+ true with the current linux pthreads, and I cannot get more than
+ 2000 simulated processes with pthreads on my box. The UNIX98
+ contexts allow me to raise the limit to 25,000 simulated processes
+ on my laptop.\n\n
+ The <tt>--with-context</tt> option of the <tt>./configure</tt>
+ script allows you to choose between UNIX98 contextes
+ (<tt>--with-context=ucontext</tt>) and the pthread version
+ (<tt>--with-context=pthread</tt>). The default value is ucontext
+ when the script detect a working UNIX98 context implementation. On
+ Windows boxes, the provided value is discarded and an adapted
+ version is picked up.\n\n
+ We experienced some issues with contextes on some rare systems
+ (solaris 8 and lower or old alpha linuxes comes to mind). The main
+ problem is that the configure script detect the contextes as being
+ functional when it's not true. If you happen to use such a system,
+ switch manually to the pthread version, and provide us with a good
+ patch for the configure script so that it is done automatically ;)
+
+ - <b>Hundred thousands of simulated processes</b> (hard-core tricks)\n
+ As explained above, SimGrid can use UNIX98 contextes to represent
+ and handle the simulated processes. Thanks to this, the main
+ limitation to the number of simulated processes becomes the
+ available memory.\n\n
+ Here are some tricks I had to use in order to run a token ring
+ between 25,000 processes on my laptop (1Gb memory, 1.5Gb swap).\n
+ - First of all, make sure your code runs for a few hundreds
+ processes before trying to push the limit. Make sure it's
+ valgrind-clean, ie that valgrind does not report neither memory
+ error nor memory leaks. Indeed, numerous simulated processes
+ result in *fat* simulation hindering debugging.
+ - It was really boring to write 25,000 entries in the deployment
+ file, so I wrote a little script
+ <tt>examples/gras/tokenS/make_deployment.pl</tt>, which you may
+ want to adapt to your case. You could also think about hijacking
+ the SURFXML parser (have look at \ref faq_flexml_bypassing).
+ - The deployment file became quite big, so I had to do what is in
+ the FAQ entry \ref faq_flexml_limit
+ - Each UNIX98 context has its own stack entry. As debugging this is
+ quite hairly, the default value is a bit overestimated so that
+ user don't get into trouble about this. You want to tune this
+ size to increse the number of processes. This is the
+ <tt>STACK_SIZE</tt> define in
+ <tt>src/xbt/context_private.h</tt>, which is 128kb by default.
+ Reduce this as much as you can, but be warned that if this value
+ is too low, you'll get a segfault. The token ring example, which
+ is quite simple, runs with 40kb stacks.
+
+\subsubsection faq_MIA_batch_scheduler Is there a native support for batch schedulers in SimGrid?
+
+No, there is no native support for batch schedulers and none is
+planned because this is a very specific need (and doing it in a
+generic way is thus very hard). However some people have implemented
+their own batch schedulers. Vincent Garonne wrote one during his PhD
+and put his code in the contrib directory of our CVS so that other can
+keep working on it. You may find inspinring ideas in it.
+
+\subsubsection faq_MIA_checkpointing I need a checkpointing thing
+
+Actually, it depends on whether you want to checkpoint the simulation, or to
+simulate checkpoints.
+
+The first one could help if your simulation is a long standing process you
+want to keep running even on hardware issues. It could also help to
+<i>rewind</i> the simulation by jumping sometimes on an old checkpoint to
+cancel recent calculations.\n
+Unfortunately, such thing will probably never exist in SG. One would have to
+duplicate all data structures because doing a rewind at the simulator level
+is very very hard (not talking about the malloc free operations that might
+have been done in between). Instead, you may be interested in the Libckpt
+library (http://www.cs.utk.edu/~plank/plank/www/libckpt.html). This is the
+checkpointing solution used in the condor project, for example. It makes it
+easy to create checkpoints (at the OS level, creating something like core
+files), and rerunning them on need.
+
+If you want to simulate checkpoints instead, it means that you want the
+state of an executing task (in particular, the progress made towards
+completion) to be saved somewhere. So if a host (and the task executing on
+it) fails (cf. #MSG_HOST_FAILURE), then the task can be restarted
+from the last checkpoint.\n
+
+Actually, such a thing does not exists in SimGrid either, but it's just
+because we don't think it is fundamental and it may be done in the user code
+at relatively low cost. You could for example use a watcher that
+periodically get the remaining amount of things to do (using
+MSG_task_get_remaining_computation()), or fragment the task in smaller
+subtasks.
+
+\subsection faq_platform Platform building and Dynamic resources
-\subsection faq_platform Building a realistic platform
+\subsubsection faq_platform Building a realistic platform
We can speak more than an hour on this subject and we still do not have
the right answer, just some ideas. You can read the following
<tt>tools/platform_generation/</tt> directory. There is a perl-script
we use to annotate a Tiers generated platform.
-\subsection faq_SURF_dynamic How can I have variable resource availability?
+\subsubsection faq_SURF_dynamic Building a dynamic platform, with resource availability
A nice feature of SimGrid is that it enables you to seamlessly have
resources whose availability change over time. When you build a
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?
+\subsubsection faq_flexml_bypassing Bypassing the XML parser with your own C functions
So you want to bypass the XML files parser, uh? Maybe doin some parameter
sweep experiments on your simulations or so? This is possible, but it's not
An example of this trick is distributed in the file examples/msg/msg_test_surfxml_bypassed.c
-\section faq_limits Pushing the limits
-
-\subsection faq_context_1000 I want thousands of simulated processes
-
-SimGrid can use either pthreads library or the UNIX98 contextes. On most
-systems, the number of pthreads is limited and then your simulation may be
-limited for a stupid reason. This is especially true with the current linux
-pthreads, and I cannot get more than 2000 simulated processes with pthreads
-on my box. The UNIX98 contexts allow me to raise the limit to 25,000
-simulated processes on my laptop.
-
-The <tt>--with-context</tt> option of the <tt>./configure</tt> script allows
-you to choose between UNIX98 contextes (<tt>--with-context=ucontext</tt>)
-and the pthread version ( (<tt>--with-context=pthread</tt>). The default
-value is ucontext when the script detect a working UNIX98 context
-implementation. On Windows boxes, the provided value is discarded and an
-adapted version is picked up.
-
-We experienced some issues with contextes on some rare systems (solaris 8
-and lower or old alpha linuxes comes to mind). The main problem is that the
-configure script detect the contextes as being functional when it's not
-true. If you happen to use such a system, switch manually to the pthread
-version, and provide us with a good patch for the configure script so that
-it is done automatically ;)
-
-\subsection faq_context_10000 I want hundred thousands of simulated processes
-
-As explained above, SimGrid can use UNIX98 contextes to represent and handle
-the simulated processes. Thanks to this, the main limitation to the number
-of simulated processes becomes the available memory.
-
-Here are some tricks I had to use in order to run a token ring between
-25,000 processes on my laptop (1Gb memory, 1.5Gb swap).
-
- - First of all, make sure your code runs for a few hundreds processes
- before trying to push the limit. Make sure it's valgrind-clean, ie that
- valgrind does not report neither memory error nor memory leaks. Indeed,
- numerous simulated processes result in *fat* simulation hindering debugging.
-
- - It was really boring to write 25,000 entries in the deployment file, so I wrote
- a little script <tt>examples/gras/tokenS/make_deployment.pl</tt>, which you may
- want to adapt to your case. You could also think about hijacking
- the SURFXML parser (have look at \ref faq_flexml_bypassing).
-
- - The deployment file became quite big, so I had to do what is in the FAQ
- entry \ref faq_flexml_limit
-
- - Each UNIX98 context has its own stack entry. As debugging this is quite
- hairly, the default value is a bit overestimated so that user don't get
- into trouble about this. You want to tune this size to increse the number
- of processes. This is the <tt>STACK_SIZE</tt> define in
- <tt>src/xbt/context_private.h</tt>, which is 128kb by default.
- Reduce this as much as you can, but be warned that if this value is too
- low, you'll get a segfault. The token ring example, which is quite simple,
- runs with 40kb stacks.
-
\section faq_troubleshooting Troubleshooting
-\subsection faq_compil_trouble ./configure fails!
+\subsection faq_trouble_compil Compilation and installation problems
+
+\subsubsection faq_trouble_config ./configure fails!
We now only one reason for the configure to fail:
If you experience other kind of issue, please get in touch with us. We are
always interested in improving our portability to new systems.
-\subsection faq_distcheck_fails Dude! "make check" fails on my machine!
+\subsubsection faq_trouble_distcheck Dude! "make check" fails on my machine!
-Don't assume we never run this target, because we do. Really. Promise!
+Don't assume we never run this target, because we do. Check
+http://bob.loria.fr:8010 if you don't believe us.
There is several reasons which may cause the make check to fail on your
machine:
libc, but it's quite undertested. For example, some (old) versions of the
glibc on alpha do not implement these functions, but provide the stubs
(which return ENOSYS: not implemented). It fools our detection mecanism
- and leads to segfaults.\n
- On some x86_64, the pointer to function is stored into a integer, but int
- are 32bits only on this arch while pointers are 64bits. Our detection
- mecanism also fails to detect the problem, which leads to segfaults.\n
- In both cases, there is not much we can do to fix the bug. We are working
- on a workaround for x86_64 machines, but in the meanwhile, you can
- compile with --with-context=pthread to avoid ucontext completely. You'll
- be a bit more limitated in the number of simulated processes you can start
- concurently, but 5000 processes is still enough for most purposes, isn't
- it?\n
+ and leads to segfaults. There is not much we can do to fix the bug.
+ A workaround is to compile with --with-context=pthread to avoid
+ ucontext completely. You'll be a bit more limitated in the number
+ of simulated processes you can start concurently, but 5000
+ processes is still enough for most purposes, isn't it?\n
This limitation is the reason why we insist on using this piece of ...
software even if it's so troublesome.\n
<b>=> use --with-pthread on AMD64 architecture that do not have an
- <b>There is a bug in SimGrid we aren't aware of</b>.\n
If none of the above apply, please drop us a mail on the mailing list so
- that we can check it out.
+ that we can check it out. Make sure to read \ref faq_bugrepport
+ before you do so.
+
+\subsection faq_trouble_errors Understanding error messages
+
+\subsubsection faq_trouble_err_logcat "gcc: _simgrid_this_log_category_does_not_exist__??? undeclared (first use in this function)"
+
+This is because you are using the log mecanism, but you didn't created
+any default category in this file. You should refer to \ref XBT_log
+for all the details, but you simply forgot to call one of
+XBT_LOG_NEW_DEFAULT_CATEGORY() or XBT_LOG_NEW_DEFAULT_SUBCATEGORY().
+
+\subsubsection faq_flexml_limit "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 without 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.
+
+<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.
+
+\subsubsection faq_trouble_gras_transport GRAS spits networking error messages
+
+Gras, on real platforms, naturally use regular sockets to communicate. They
+are deeply hiden in the gras abstraction, but when things go wrong, you may
+get some weird error messages. Here are some example, with the probable
+reason:
-\subsection faq_longjmp longjmp madness in valgrind
+ - <b>Transport endpoint is not connected</b>: several processes try to open
+ a server socket on the same port number of the same machine. This is
+ naturally bad and each process should pick its own port number for this.\n
+ Maybe, you just have some processes remaining from a previous experiment
+ on your machine.\n
+ Killing them may help, but again if you kill -KILL them, you'll have to
+ wait for a while: they didn't close there sockets properly and the system
+ needs a while to notice that this port is free again.
+
+ - <b>Socket closed by remote side</b>: if the remote process is not
+ supposed to close the socket at this point, it may be dead.
+
+ - <b>Connection reset by peer</b>: I found this on internet about this
+ error. I think it's what's happening here, too:\n
+ <i>This basically means that a network error occurred while the client was
+ receiving data from the server. But what is really happening is that the
+ server actually accepts the connection, processes the request, and sends
+ a reply to the client. However, when the server closes the socket, the
+ client believes that the connection has been terminated abnormally
+ because the socket implementation sends a TCP reset segment telling the
+ client to throw away the data and report an error.\n
+ Sometimes, this problem is caused by not properly closing the
+ input/output streams and the socket connection. Make sure you close the
+ input/output streams and socket connection properly. If everything is
+ closed properly, however, and the problem persists, you can work around
+ it by adding a one-second sleep before closing the streams and the
+ socket. This technique, however, is not reliable and may not work on all
+ systems.</i>\n
+ Since GRAS sockets are closed properly (repeat after me: there is no bug
+ in GRAS), it is either that you are closing your sockets on server side
+ before the client get a chance to read them (use gras_os_sleep() to delay
+ the server), or the server died awfully before the client got the data.
+
+\subsubsection faq_trouble_errors_big_fat_warning I'm told that my XML files are too old.
+
+We have decided to change the units in SimGrid. Now we use Bytes, Flops and
+seconds instead of MBytes, MFlops and seconds... Units should be updated
+accordingly and the version of platform_description should be set to a
+valuer greater than 1:
+\verbatim
+ <platform_description version="1">
+\endverbatim
+You should try to use the surfxml_update.pl script that can be found
+<a href="http://gforge.inria.fr/plugins/scmcvs/cvsweb.php/contrib/platform_generation/?cvsroot=cvsroot%2Fsimgrid">here</a>.
+
+\subsection faq_trouble_valgrind Valgrind-related issues
+
+If you don't, you really should use valgrind to debug your code, it's
+almost magic.
+
+\subsubsection faq_trouble_vg_longjmp longjmp madness in valgrind
This is when valgrind starts complaining about longjmp things, just like:
block. This is <b>evil</b>, and you must not do this. Did you read the section
about \ref XBT_ex??
-\subsection faq_valgrind Valgrind spits tons of errors!
+\subsubsection faq_trouble_vg_libc Valgrind spits tons of errors about backtraces!
It may happen that valgrind, the memory debugger beloved by any decent C
programmer, spits tons of warnings like the following :
\verbatim export VALGRIND_OPTS="--leak-check=yes --leak-resolution=high --num-callers=40 --tool=memcheck --suppressions=$HOME/.valgrind.supp" \endverbatim
-\subsection 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 without 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.
-
-\subsection faq_gras_transport GRAS spits networking error messages
-
-Gras, on real platforms, naturally use regular sockets to communicate. They
-are deeply hiden in the gras abstraction, but when things go wrong, you may
-get some weird error messages. Here are some example, with the probable
-reason:
-
- - <b>Transport endpoint is not connected</b>: several processes try to open
- a server socket on the same port number of the same machine. This is
- naturally bad and each process should pick its own port number for this.\n
- Maybe, you just have some processes remaining from a previous experiment
- on your machine.\n
- Killing them may help, but again if you kill -KILL them, you'll have to
- wait for a while: they didn't close there sockets properly and the system
- needs a while to notice that this port is free again.
-
- - <b>Socket closed by remote side</b>: if the remote process is not
- supposed to close the socket at this point, it may be dead.
-
- - <b>Connection reset by peer</b>: I found this on internet about this
- error. I think it's what's happening here, too:\n
- <i>This basically means that a network error occurred while the client was
- receiving data from the server. But what is really happening is that the
- server actually accepts the connection, processes the request, and sends
- a reply to the client. However, when the server closes the socket, the
- client believes that the connection has been terminated abnormally
- because the socket implementation sends a TCP reset segment telling the
- client to throw away the data and report an error.\n
- Sometimes, this problem is caused by not properly closing the
- input/output streams and the socket connection. Make sure you close the
- input/output streams and socket connection properly. If everything is
- closed properly, however, and the problem persists, you can work around
- it by adding a one-second sleep before closing the streams and the
- socket. This technique, however, is not reliable and may not work on all
- systems.</i>\n
- Since GRAS sockets are closed properly (repeat after me: there is no bug
- in GRAS), it is either that you are closing your sockets on server side
- before the client get a chance to read them (use gras_os_sleep() to delay
- the server), or the server died awfully before the client got the data.
-
-\subsection faq_deadlock There is a deadlock !!!
+\subsection faq_deadlock There is a deadlock in my code!!!
Unfortunately, we cannot debug every code written in SimGrid. We
furthermore believe that the framework provides ways enough
on your side... We have plenty of FAQ entries to redact and new
features to implement for the impenitents! ;)
-\subsection faq_big_fat_warning A BIG FAT WARNING is reported telling me that my platform and deployment files are too old.
-
-We have decided to change the units in SimGrid. Now we use Bytes, Flops and
-seconds instead of MBytes, MFlops and seconds... Units should be updated
-accordingly and the version of platform_description should be set to a
-valuer greater than 1:
-\verbatim
- <platform_description version="1">
-\endverbatim
-You should try to use the surfxml_update.pl script that can be found
-<a href="http://gforge.inria.fr/plugins/scmcvs/cvsweb.php/contrib/platform_generation/?cvsroot=cvsroot%2Fsimgrid">here</a>.
-
\subsection faq_surf_network_latency I get weird timings when I play with the latencies.
OK, first of all, remember that units should be Bytes, Flops and
