From ffb4f53786186038947a9c9159b93c80f5c7b76a Mon Sep 17 00:00:00 2001 From: Martin Quinson Date: Sun, 1 Apr 2012 17:16:45 -1000 Subject: [PATCH] You cannot say that SMPI has no documentation anymore but you probably still can say that its documentation is too sparse for absolute beginners. People used to MPI should find it sufficient however. --- doc/modules.doc | 109 +++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 93 insertions(+), 16 deletions(-) diff --git a/doc/modules.doc b/doc/modules.doc index 76e25a142c..b5b7ce8779 100644 --- a/doc/modules.doc +++ b/doc/modules.doc @@ -79,25 +79,102 @@ \ingroup SimGrid_API \brief Programming environment for the simulation of MPI applications - Once implemented, this programming environment will allow you to study - within the simulator any MPI application without having to modify them - for that. In other words, it will constitute an emulation solution for - parallel codes. +This programming environment permits to study existing MPI application +by emulating them on top of the SimGrid simulator. In other words, it +will constitute an emulation solution for parallel codes. You don't +even have to modify your code for that, although that may help, as +detailed below. - \section SMPI_who Who should use this (and who shouldn't) +\section SMPI_who Who should use SMPI (and who shouldn't) - You should use this programming environment of the SimGrid suite if you - want to study existing MPI applications. - If you want to work on a distributed application, have a look at the - \ref GRAS_API environment. - If you want to study some heuristics for a given problem (and if your - goal is to produce theorems, not code), have a look at the \ref MSG_API - environment, or the \ref SD_API one if you need to use DAGs. - If none of those programming environments fits your needs, you may - consider implementing your own directly on top of \ref SURF_API (but you - probably want to contact us before). +You should use this programming environment of the SimGrid suite if +you want to study existing MPI applications. If you want to create a +distributed application, you may be interested in the \ref GRAS_API +environment instead (but note that GRAS is not very actively +maintained nowadays). If you want to study some heuristics for a given +problem (and if your goal is to produce theorems and publications, not +code), have a look at the \ref MSG_API environment, or the \ref SD_API +one if you need to use DAGs. If none of those programming environments +fits your needs, you may consider implementing your own directly on +top of \ref SURF_API (but you probably want to contact us before). - */ +\section SMPI_what What can run within SMPI? + +You can run unmodified MPI applications (both C and Fortran) within +SMPI, provided you only use MPI calls that we implemented in MPI. Our +coverage of the interface is not bad, but will probably never be +complete. One sided communications and I/O primitives are not targeted +for now. The full list of not yet implemented functions is available +in file include/smpi/smpi.h of the archive, between two lines +containing the FIXME marker. If you really need a missing +feature, please get in touch with us: we can guide you though the +SimGrid code to help you implementing it, and we'd glad to integrate +it in the main project afterward if you contribute them back. + +\section SMPI_adapting Adapting your MPI code to the use of SMPI + +As detailed in the reference article (available at +http://hal.inria.fr/inria-00527150), you may want to adapt your code +to improve the simulation performance. But these tricks may seriously +hinder the result qualtity (or even prevent the app to run) if used +wrongly. We assume that if you want to simulate an HPC application, +you know what you are doing. Don't prove us wrong! + +If you get short on memory (the whole app is executed on a single node +when simulated), you should have a look at the SMPI_SHARED_MALLOC and +SMPI_SHARED_FREE macros. It allows to share memory areas between +processes. For example, matrix multiplication code may want to store +the blocks on the same area. Of course, the resulting computations +will useless, but you can still study the application behavior this +way. Of course, if your code is data-dependent, this won't work. + +If your application is too slow, try using SMPI_SAMPLE_LOCAL, +SMPI_SAMPLE_GLOBAL and friends to indicate which computation loops can +be sampled. Some of the loop iterations will be executed to measure +their duration, and this duration will be used for the subsequent +iterations. These samples are done per processor with +SMPI_SAMPLE_LOCAL, and shared between all processors with +SMPI_SAMPLE_GLOBAL. Of course, none of this will work if the execution +time of your loop iteration are not stable. + +Yes, that's right, these macros are not documented yet, but we'll fix +it as soon as time permits. Sorry about that -- patch welcomed! + +\section SMPI_compiling Compiling your code + +This is very simply done with the smpicc script. If you +already compiled any MPI code before, you already know how to use it. +If not, you should try to get your MPI code running on top of MPI +before giving SMPI a spin. Actually, that's very simple even if it's +the first time you use MPI code: just use smpicc as a compiler (in +replacement of gcc or your usual compiler), and you're set. + +\section SMPI_executing Executing your code on top of the simulator + +This is done though the smpirun script as follows. +my_hostfile.txt is a classical MPI hostfile (that is, this +file lists the machines on which the processes must be dispatched, one +per line) my_platform.xml is a classical SimGrid platform +file. Of course, the hosts of the hostfile must exist in the provided +platform. ./program is the MPI program that you want to +simulate (must be compiled by smpicc) while -arg is +a command-line parameter passed to this program. + +\verbatim +smpirun -hostfile my_hostfile.txt -platform my_platform.xml ./program -arg +\endverbatim + +smpirun accepts other parameters, such as -np if you don't +want to use all the hosts defined in the hostfile, -map to +display on which host each rank gets mapped of -trace to +activate the tracing during the simulation. You can get the full list +by running +\verbatim +smpirun -help +\endverbatim + + +*/ /** \defgroup SD_API SimDag -- 2.20.1