You are at the right place... To understand what you can do or
cannot do with SimGrid, you should read the
-<a href="http://simgrid.gforge.inria.fr/tutorials.php">tutorial
-slides</a> from the SimGrid's website. You may find more uptodate
+<a href="https://simgrid.org/tutorials.html">tutorial
+slides</a> from the SimGrid's website. You may find more up-to-date
material on the
<a href="http://people.irisa.fr/Martin.Quinson/blog/SimGrid/">blog of
-Martin Quinson</a>.
+Martin Quinson</a>.
Another great source of inspiration can be found in the @ref s4u_examples.
If you are stuck at any point and if this FAQ cannot help you, please drop us a
-mail to the user mailing list: <simgrid-user@lists.gforge.inria.fr>.
-
-@subsection faq_interfaces What is the difference between MSG and SimDag? 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. This is the interface of choice for people wanting to port old
-code designed for SimGrid v1 or v2 to the framework current version.
-
-With MSG, your application is seen as a set of communicating
-processes, exchanging data by the way of messages and performing
-computation on their own.
+mail to the user mailing list: <simgrid-community@inria.fr>.
@subsection faq_visualization Visualizing and analyzing the results
We also have a more graphical output. Have a look at section @ref options_tracing.
-@subsection faq_C Argh! Do I really have to code in C?
-
-We provide Java bindings of the MSG interface, which is the main
-SimGrid user API.
-
-Moreover 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).
-
-For now, we do not feel a real demand for any other language. But if
-you think there is one, please speak up!
-
@section faq_howto Feature related questions
@subsection faq_MIA "Could you please add (your favorite feature here) to SimGrid?"
@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
-examples.
-
-Of course they have often been needing more complex functions like
-MSG_process_suspend(), MSG_process_resume() and
-MSG_process_isSuspended() (to perform synchronization), or
-MSG_task_Iprobe() and MSG_process_sleep() (to avoid blocking
-receptions), or even MSG_process_create() (to design asynchronous
-communications or computations). But the examples are sufficient to
-start.
-
-We know. We should add some more examples, but not really some more
-complex ones... We should add some examples that illustrate some other
-functionalists (like how to simply encode asynchronous
-communications, RPC, process migrations, thread synchronization, ...)
-and we will do it when we will have a little bit more time. We have
-tried to document the examples so that they are understandable. Tell
-us if something is not clear and once again feel free to participate!
-:)
-
-@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
-this task, he doesn't have this task anymore. It's gone. The receiver
-process has got the task. However, you could decide upon receiving to
-create a "copy" of a task but you have to handle by yourself the
-semantic associated to this "duplication".
-
-As we already told, we prefer keeping the API as simple as
-possible. This kind of feature is rather easy to implement by users
-and the semantic you associate really depends on people. Having a
-*generic* task duplication mechanism is not that trivial (in
-particular because of the data field). That is why I would recommend
-that you write it by yourself even if I can give you advice on how to
-do it.
-
-You have the following functions to get information about a task:
-MSG_task_get_name(), MSG_task_get_compute_duration(),
-MSG_task_get_remaining_computation(), MSG_task_get_data_size(),
-and MSG_task_get_data().
-
-You could use a dictionary (#xbt_dict_t) of dynars (#xbt_dynar_t). If
-you still don't see how to do it, please come back to us...
-
@subsubsection faq_MIA_thread_synchronization How to synchronize my user processes?
It depends on why you want to synchronize them. If you just want to
If you really need to synchronize your processes (because it's what
you are studying or to create an atomic section that spans over
several simcalls), you obviously cannot use regular synchronization
-mechanisms (pthread_mutexes in C or the synchronized keyword in Java).
+mechanisms (pthread_mutexes in C).
This is because the SimGrid kernel locks all processes and unlock them
one after the other when they are supposed to run, until they give the
-control back in their simcall. If one of them gets locked by the OS
+control back in their simcall. If one of them gets locked by the OS
before returning the control to the kernel, that's definitively a
deadlock.
Instead, you should use the synchronization mechanism provided by the
simulation kernel. This could with a SimGrid mutex, a SimGrid
condition variables or a SimGrid semaphore, as described in @ref
-msg_synchro (in Java, only semaphores are available). But actually,
+msg_synchro. But actually,
many synchronization patterns can be encoded with communication on
mailboxes. Typically, if you need one process to notify another one,
-you could use a condition variable or a semphore, but sending a
+you could use a condition variable or a semaphore, but sending a
message to a specific mailbox does the trick in most cases.
-@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,
-but there is as many definition of "host load" as people asking for
-this function. First, you have to remember that resource availability
-may vary over time, which make any load notion harder to define.
-
-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?
-
-First of all, it's near to impossible to predict the load beforehand in the
-simulator since it depends on too much parameters (background load
-variation, bandwidth sharing algorithmic complexity) some of them even being
-not known beforehand (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.
-
-@code
-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);
-}
-@endcode
-
-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.
-
@subsubsection faq_MIA_communication_time How can I get the *real* communication time?
Communications are synchronous and thus if you simply get the time
m_task_t task = MSG_task_create("Task", task_comp_size, task_comm_size,
calloc(1,sizeof(double)));
*((double*) task->data) = MSG_get_clock();
- MSG_task_put(task, slaves[i % slaves_count], PORT_22);
+ MSG_task_put(task, workers[i % workers_count], PORT_22);
XBT_INFO("Send completed");
return 0;
}
and put his code in the contrib directory of our SVN so that other can
keep working on it. You may find inspiring 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 exist 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
-@subsubsection faq_platform_example Where can I find SimGrid platform files?
-
-There are several little examples in the archive, in the examples/msg
-directory. From time to time, we are asked for other files, but we
-don't have much at hand right now.
-
-You should refer to the Platform Description Archive
-(http://pda.gforge.inria.fr) project to see the other platform file we
-have available, as well as the Simulacrum simulator, meant to generate
-SimGrid platforms using all classical generation algorithms.
-
-@subsubsection faq_platform_alnem How can I automatically map an existing platform?
-
-We are working on a project called ALNeM (Application-Level Network
-Mapper) which goal is to automatically discover the topology of an
-existing network. Its output will be a platform description file
-following the SimGrid syntax, so everybody will get the ability to map
-their own lab network (and contribute them to the catalog project).
-This tool is not ready yet, but it move quite fast forward. Just stay
-tuned.
-
@subsubsection faq_platform_synthetic Generating synthetic but realistic platforms
-The third possibility to get a platform file (after manual or
-automatic mapping of real platforms) is to generate synthetic
+Another possibility to get a platform file is to generate synthetic
platforms. Getting a realistic result is not a trivial task, and
moreover, nobody is really able to define what "realistic" means when
speaking of topology files. You can find some more thoughts on this
note that although sound, this model were never scientifically
assessed. Please keep this fact in mind when using it.
-
-@subsubsection faq_platform_random Using random variable for the resource power or availability
-
-The best way to model the resouce power using a random variable is to
-use an availability trace that is directed by a probability
-distribution. This can be done using the function
-tmgr_trace_generator_value() below. The date and value generators is
-created with one of tmgr_event_generator_new_uniform(),
-tmgr_event_generator_new_exponential() or
-tmgr_event_generator_new_weibull() (if you need other generators,
-adding them to src/surf/trace_mgr.c should be quite trivial and your
-patch will be welcomed). Once your trace is created, you have to
-connect it to the resource with the function
-sg_platf_new_trace_connect().
-
-That the process is very similar if you want to model the
-resource availability with a random variable (deciding whether it's
-on/off instead of deciding its speed) using the function
-tmgr_trace_generator_state() or tmgr_trace_generator_avail_unavail()
-instead of tmgr_trace_generator_value().
-
-Unfortunately, all this is currently lacking a proper documentation,
-and there is even no proper example of use. You'll thus have to check
-the header file include/simgrid/platf.h and experiment a bit by
-yourself. The following code should be a good starting point, and
-contributing a little clean example would be a good way to help the
-SimGrid project.
-
-@code
-tmgr_trace_generator_value("mytrace",tmgr_event_generator_new_exponential(.5)
- tmgr_event_generator_new_uniform(100000,9999999));
-
-sg_platf_trace_connect_cbarg_t myconnect = SG_PLATF_TRACE_CONNECT_INITIALIZER;
-myconnect.kind = SURF_TRACE_CONNECT_KIND_BANDWIDTH;
-myconnect.trace = "mytrace";
-myconnect.element = "mylink";
-
-sg_platf_trace_connect(myconnect);
-@endcode
-
@section faq_troubleshooting Troubleshooting
-@subsection faq_trouble_changelog The feature X stopped to work after my last update
-
-I guess that you want to read the ChangeLog file, that always contains
-all the information that could be important to the users during the
-upgrade. Actually, you may want to read it (alongside with the NEWS
-file that highlights the most important changes) even before you
-upgrade your copy of SimGrid, too.
-
-We do our best to maintain the backward compatibility, but we
-sometimes have to fix the things that are too broken. If we happen to
-kill a feature that you were using, we are sorry. We think that you
-should update to the new way of doing things, but if you can't afford
-it, that's ok. Just stick to the last version that were working for
-you, and have a pleasant day.
-
-@subsection faq_trouble_lib_compil SimGrid compilation and installation problems
-
-@subsubsection faq_trouble_lib_config cmake fails!
-
-We know only one reason for the configure to fail:
-
- - <b>You are using a broken build environment</b>@n
- Try updating your cmake version. If symptom is that the configury
- magic complains about gcc not being able to build executables, you
- are probably missing the libc6-dev package. Damn Ubuntu.
-
-If you experience other kind of issue, please get in touch with us. We are
-always interested in improving our portability to new systems.
-
-@subsubsection faq_trouble_distcheck Dude! "ctest" fails on my machine!
-
-Don't assume we never run this target, because we do. Check
-http://cdash.inria.fr/CDash/index.php?project=Simgrid (click on
-previous if there is no result for today: results are produced only by
-11am, French time) and
-https://buildd.debian.org/status/logs.php?pkg=simgrid if you don't believe us.
-
-If it's failing on your machine in a way not experienced by the
-autobuilders above, please drop us a mail on the mailing list so that
-we can check it out. Make sure to read @ref faq_bugrepport before you
-do so.
-
-@subsection faq_trouble_compil User code compilation problems
-
-@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 mechanism, 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_trouble_pthreadstatic "gcc: undefined reference to pthread_key_create"
-
-This indicates that one of the library SimGrid depends on (libpthread
-here) was missing on the linking command line. Dependencies of
-libsimgrid are expressed directly in the dynamic library, so it's
-quite impossible that you see this message when doing dynamic linking.
-
-If you compile your code statically (and if you use a pthread version
-of SimGrid), you must absolutely
-specify <tt>-lpthread</tt> on the linker command line. As usual, this should
-come after <tt>-lsimgrid</tt> on this command line.
-
-@subsection faq_trouble_errors Runtime error messages
-
-@subsubsection faq_trouble_errors_big_fat_warning I'm told that my XML files are too old.
-
-The format of the XML platform description files is sometimes
-improved. For example, we decided to change the units used in SimGrid
-from MBytes, MFlops and seconds to Bytes, Flops and seconds to ease
-people exchanging small messages. We also reworked the route
-descriptions to allow more compact descriptions.
-
-That is why the XML files are versionned using the 'version' attribute
-of the root tag. Currently, it should read:
-@verbatim
- <platform version="4">
-@endverbatim
-
-If your files are too old, you can use the simgrid_update_xml.pl
-script which can be found in the tools directory of the archive.
-
-@subsection faq_trouble_debug Debugging SMPI applications
-
-In order to debug SMPI programs, you can use the following options:
-
-- <b>-wrapper 'gdb --args'</b>: this option is used to use a wrapper
- in order to call the SMPI process. Good candidates for this options
- are "gdb --args", "valgrind", "rr record", "strace", etc;
-
-- <b>-foreground</b>: this options gives the debugger access to the terminal
- which is needed in order to use an interactive debugger.
-
-Both options are needed in order to run the SMPI process under GDB.
-
-@subsection faq_trouble_valgrind Valgrind-related and other debugger issues
-
-If you don't, you really should use valgrind to debug your code, it's
-almost magic.
-
-@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 ==8414== Conditional jump or move depends on uninitialised value(s)
-==8414== at 0x400882D: (within /lib/ld-2.3.6.so)
-==8414== by 0x414EDE9: (within /lib/tls/i686/cmov/libc-2.3.6.so)
-==8414== by 0x400B105: (within /lib/ld-2.3.6.so)
-==8414== by 0x414F937: _dl_open (in /lib/tls/i686/cmov/libc-2.3.6.so)
-==8414== by 0x4150F4C: (within /lib/tls/i686/cmov/libc-2.3.6.so)
-==8414== by 0x400B105: (within /lib/ld-2.3.6.so)
-==8414== by 0x415102D: __libc_dlopen_mode (in /lib/tls/i686/cmov/libc-2.3.6.so)
-==8414== by 0x412D6B9: backtrace (in /lib/tls/i686/cmov/libc-2.3.6.so)
-==8414== by 0x8076446: xbt_dictelm_get_ext (dict_elm.c:714)
-==8414== by 0x80764C1: xbt_dictelm_get (dict_elm.c:732)
-==8414== by 0x8079010: xbt_cfg_register (config.c:208)
-==8414== by 0x806821B: MSG_config (msg_config.c:42)
-@endverbatim
-
-This problem is somewhere in the libc when using the backtraces and there is
-very few things we can do ourselves to fix it. Instead, here is how to tell
-valgrind to ignore the error. Add the following to your ~/.valgrind.supp (or
-create this file on need). Make sure to change the obj line according to
-your personnal mileage (change 2.3.6 to the actual version you are using,
-which you can retrieve with a simple "ls /lib/ld*.so").
-
-@verbatim {
- name: Backtrace madness
- Memcheck:Cond
- obj:/lib/ld-2.3.6.so
- fun:dl_open_worker
- fun:_dl_open
- fun:do_dlopen
- fun:dlerror_run
- fun:__libc_dlopen_mode
-}@endverbatim
-
-Then, you have to specify valgrind to use this suppression file by passing
-the <tt>--suppressions=$HOME/.valgrind.supp</tt> option on the command line.
-You can also add the following to your ~/.bashrc so that it gets passed
-automatically. Actually, it passes a bit more options to valgrind, and this
-happen to be my personnal settings. Check the valgrind documentation for
-more information.
-
-@verbatim export VALGRIND_OPTS="--leak-check=yes --leak-resolution=high --num-callers=40 --tool=memcheck --suppressions=$HOME/.valgrind.supp" @endverbatim
-
-@subsubsection faq_trouble_backtraces Truncated backtraces
-
-When debugging SimGrid, it's easier to pass the
---disable-compiler-optimization flag to the configure if valgrind or
-gdb get fooled by the optimization done by the compiler. But you
-should remove these flag when everything works before going in
-production (before launching your 1252135 experiments), or everything
-will run only one half of the true SimGrid potential.
-
-@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
-information to debug such information yourself. If the textual output
-is not enough, Make sure to check the @ref faq_visualization FAQ entry to see
-how to get a graphical one.
-
-Now, if you come up with a really simple example that deadlocks and
-you're absolutely convinced that it should not, you can ask on the
-list. Just be aware that you'll be severely punished if the mistake is
-on your side... We have plenty of FAQ entries to redact and new
-features to implement for the impenitents! ;)
-
@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
competing on a saturated link receive an amount of bandwidth inversely
proportional to their round trip time.
-@subsection faq_bugrepport So I've found a bug in SimGrid. How to report it?
-
-We do our best to make sure to hammer away any bugs of SimGrid, but this is
-still an academic project so please be patient if/when you find bugs in it.
-If you do, the best solution is to drop an email either on the simgrid-user
-or the simgrid-devel mailing list and explain us about the issue. You can
-also decide to open a formal bug report using the
-<a href="https://gforge.inria.fr/tracker/?atid=165&group_id=12&func=browse">relevant
-interface</a>. You need to login on the server to get the ability to submit
-bugs.
-
-We will do our best to solve any problem repported, but you need to help us
-finding the issue. Just telling "it segfault" isn't enough. Telling "It
-segfaults when running the attached simulator" doesn't really help either.
-You may find the following article interesting to see how to repport
-informative bug repports:
-http://www.chiark.greenend.org.uk/~sgtatham/bugs.html (it is not SimGrid
-specific at all, but it's full of good advices).
-
*/
