simulation kernel (default value: 1e-6). Please note that in some
circonstances, this optimization can hinder the simulation accuracy.
+If the "application" is in fact doing a "live replay" of another MPI
+app (e.g., ScalaTrace's replay tool, various on-line simulators that
+run an app at scale), the computation due to the replay logic should
+not be simulated by SMPI. In that case the \b
+smpi/simulation_computation item can be set to 'no' causing all the
+compute bursts between MPI calls to be ignored by SMPI. Then only the
+communications are simulated. This implies to add explicit calls to \c
+smpi_execute() in the "application" to simulate computations.
+
+
\subsection options_smpi_timing Reporting simulation time
Most of the time, you run MPI code through SMPI to compute the time it
Simulation time: 1e3 seconds.
\endverbatim
-\subsection options_model_smpi_detached Simulating MPI detached send
+\subsection options_smpi_global Automatic privatization of global variables
+
+MPI executables are meant to be executed in separated processes, but SMPI is
+executed in only one process. Global variables from executables will be placed
+in the same memory zone and shared between processes, causing hard to find bugs.
+To avoid this, several options are possible :
+ - Manual edition of the code, for example to add __thread keyword before data
+ declaration, which allows the resulting code to work with SMPI, but only
+ if the thread factory (see \ref options_virt_factory) is used, as global
+ variables are then placed in the TLS (thread local storage) segment.
+ - Source-to-source transformation, to add a level of indirection
+ to the global variables. SMPI does this for F77 codes compiled with smpiff,
+ and used to provide coccinelle scripts for C codes, which are not functional anymore.
+ - Compilation pass, to have the compiler automatically put the data in
+ an adapted zone.
+ - Runtime automatic switching of the data segments. SMPI stores a copy of
+ each global data segment for each process, and at each context switch replaces
+ the actual data with its copy from the right process. This mechanism uses mmap,
+ and is for now limited to systems supporting this functionnality (all Linux
+ and some BSD should be compatible).
+ Another limitation is that SMPI only accounts for global variables defined in
+ the executable. If the processes use external global variables from dynamic
+ libraries, they won't be switched correctly. To avoid this, using static
+ linking is advised (but not with the simgrid library, to avoid replicating
+ its own global variables).
+
+ To use this runtime automatic switching, the variable \b smpi/privatize_global_variables
+ should be set to yes
+
-(this configuration item is experimental and may change or disapear)
+
+\subsection options_model_smpi_detached Simulating MPI detached send
This threshold specifies the size in bytes under which the send will return
immediately. This is different from the threshold detailed in \ref options_model_network_asyncsend
uses naive version of collective operations). Each collective operation can be manually selected with a
\b smpi/collective_name:algo_name. Available algorithms are listed in \ref SMPI_collective_algorithms .
+\subsection options_model_smpi_computation_simulation Benchmarking/simulating application computation
+
+By default, SMPI benchmarks computational phases of the simulated application (i.e., CPU bursts in
+between MPI calls) so that these phases can be simulated. In some cases, however, one may wish to
+disable simulation of application computation. This is the case when SMPI is used not to simulate
+an MPI applications, but instead an MPI code that performs "live replay" of another MPI app (e.g.,
+ScalaTrace's replay tool, various on-line simulators that run an app at scale). In this case the
+computation of the replay/simulation logic should not be simulated by SMPI. Instead, the replay
+tool or on-line simulator will issue "computation events", which correspond to the actual MPI simulation
+being replayed/simulated. At the moment, these computation events can be simulated using SMPI by
+calling internal smpi_execute*() functions.
+
+To disable the benchmarking/simulation of computation in the simulated application via this runtime automatic
+switching, the variable \b smpi/privatize_global_variables should be set to no
+
\section options_generic Configuring other aspects of SimGrid
\subsection options_generic_path XML file inclusion path
- \c surf/nthreads: \ref options_model_nthreads
+- \c smpi/simulation_computation: \ref options_smpi_bench
- \c smpi/running_power: \ref options_smpi_bench
- \c smpi/display_timing: \ref options_smpi_timing
- \c smpi/cpu_threshold: \ref options_smpi_bench
- \c smpi/async_small_thres: \ref options_model_network_asyncsend
- \c smpi/send_is_detached: \ref options_model_smpi_detached
- \c smpi/coll_selector: \ref options_model_smpi_collectives
+- \c smpi/privatize_global_variables: \ref options_smpi_global
- \c path: \ref options_generic_path
- \c verbose-exit: \ref options_generic_exit
