so that you don't have to give <tt>--cfg=model-check:1</tt> in
addition.
+\subsection options_mc_perf Performance considerations for the model checker
+
+The size of the stacks can have a huge impact on the memory
+consumption when using model-checking. Currently each snapshot, will
+save a copy of the whole stack and not only of the part which is
+really meaningful: you should expect the contribution of the memory
+consumption of the snapshots to be \f$ \mbox{number of processes}
+\times \mbox{stack size} \times \mbox{number of states} \f$.
+
+However, when compiled against the model checker, the stacks are not
+protected with guards: if the stack size is too small for your
+application, the stack will silently overflow on other parts of the
+memory.
+
\section options_virt Configuring the User Process Virtualization
\subsection options_virt_factory Selecting the virtualization factory
rather disturbing: this leads to stack overflow (overwriting other
stacks), leading to segfaults with corrupted stack traces.
-If you want to push the scalability limits of your code, you really
+If you want to push the scalability limits of your code, you might
want to reduce the \b contexts/stack_size item. Its default value
is 8192 (in KiB), while our Chord simulation works with stacks as small
as 16 KiB, for example. For the thread factory, the default value
is the one of the system, if it is too large/small, it has to be set
with this parameter.
+The operating system should only allocate memory for the pages of the
+stack which are actually used and you might not need to use this in
+most cases. However, this setting is very important when using the
+model checker (see \ref options_mc_perf).
+
+In some cases, no stack guard page is used and the stack will silently
+overflow on other parts of the memory if the stack size is too small
+for your application. This happens :
+
+- on Windows systems;
+- when the model checker is enabled;
+- when stack guard pages are explicitely disabled (see \ref options_perf_guard_size).
+
\subsection options_virt_parallel Running user code in parallel
Parallel execution of the user code is only considered stable in
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.
-
+ 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, the variable \b
+smpi/simulation_computation should be set to no
\subsection options_smpi_timing Reporting simulation time
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
It can be done by using XBT. Go to \ref XBT_log for more details.
+\section options_perf Performance optimizations
+
+\subsection options_perf_context Context factory
+
+In order to achieve higher performance, you might want to use the raw
+context factory which avoids any system call when switching between
+tasks. If it is not possible you might use ucontext instead.
+
+\subsection options_perf_guard_size Disabling stack guard pages
+
+A stack guard page is usually used which prevents the stack from
+overflowing on other parts of the memory. However this might have a
+performance impact if a huge number of processes is created. The
+option \b contexts:guard_size is the number of stack guard pages
+used. By setting it to 0, no guard pages will be used: in this case,
+you should avoid using small stacks (\b stack_size) as the stack will
+silently overflow on other parts of the memory.
\section options_index Index of all existing configuration items
- \c contexts/parallel_threshold: \ref options_virt_parallel
- \c contexts/stack_size: \ref options_virt_stacksize
- \c contexts/synchro: \ref options_virt_parallel
+- \c contexts/guard_size: \ref options_virt_parallel
- \c cpu/maxmin_selective_update: \ref options_model_optim
- \c cpu/model: \ref options_model_select
