There is several way to pass configuration options to the simulators.
The most common way is to use the \c --cfg command line argument. For
-example, to set the variable \c Variable to the value \c Value, simply
+example, to set the item \c Item to the value \c Value, simply
type the following: \verbatim
-my_simulator --cfg=Variable:Value (other arguments)
+my_simulator --cfg=Item:Value (other arguments)
\endverbatim
Several \c --cfg command line arguments can naturally be used. If you
The \c \<config\> tag takes an \c id attribute, but it is currently
ignored so you don't really need to pass it. The important par is that
within that tag, you can pass one or several \c \<prop\> tags to specify
-the configuration to use. For example, setting \c Variable to \c Value
+the configuration to use. For example, setting \c Item to \c Value
can be done by adding the following to the beginning of your platform
file: \verbatim
<config>
- <prop id="Variable" value="Value"/>
+ <prop id="Item" value="Value"/>
</config>
\endverbatim
A last solution is to pass your configuration directly using the C
interface. Unfortunately, this path is not really easy to use right
-now, and you mess directly with surf variables as follows. Check the
+now, and you mess directly with surf internal variables as follows. Check the
\ref XBT_config "relevant page" for details on all the functions you
-can use in this context (\c _surf_cfg_set is the only configuration set
-currently used in SimGrid). \code
+can use in this context, \c _surf_cfg_set being the only configuration set
+currently used in SimGrid. \code
#include <xbt/config.h>
extern xbt_cfg_t _surf_cfg_set;
int main(int argc, char *argv[]) {
MSG_global_init(&argc, argv);
- xbt_cfg_set_parse(_surf_cfg_set,"Variable:Value");
+ xbt_cfg_set_parse(_surf_cfg_set,"Item:Value");
// Rest of your code
}
SimGrid comes with several network and CPU models built in, and you
can change the used model at runtime by changing the passed
-configuration. The three main configuration variables are given below.
-For each of these variable, passing the special \c help value gives
-you a short description of all possible values.
+configuration. The three main configuration items are given below.
+For each of these items, passing the special \c help value gives
+you a short description of all possible values. Also, \c --help-models
+should provide information about all models for all existing resources.
- \b network/model: specify the used network model
- \b cpu/model: specify the used CPU model
- \b workstation/model: specify the used workstation model
realism, but is (marginally) faster.
- \b SMPI: Realistic network model specifically tailored for HPC
settings (accurate modeling of slow start with correction factors on
- three intervals: < 1KiB, < 64 KiB, >= 64 KiB)
+ three intervals: < 1KiB, < 64 KiB, >= 64 KiB). See also \ref
+ options_model_network_coefs "this section" for more info.
- \b CM02: Legacy network analytic model (Very similar to LV08, but
without corrective factors. The timings of small messages are thus
poorly modeled)
If you compiled SimGrid accordingly, you can use packet-level network
simulators as network models (see \ref pls). In that case, you have
-two extra models:
+two extra models, described below, and some \ref options_pls "specific
+additional configuration flags".
- \b GTNets: Network pseudo-model using the GTNets simulator instead
of an analytic model
- \b NS3: Network pseudo-model using the NS3 tcp model instead of an
- \b ptask_L07: Workstation model somehow similar to Cas01+CM02 but
allowing parallel tasks
-Finally, the network and CPU models that are based on lmm_solve (that
+\subsection options_model_optim Optimization level of the platform models
+
+The network and CPU models that are based on lmm_solve (that
is, all our analytical models) accept specific optimization
-configurations (through the \b network/optim and \b CPU/optim
-variables). The accepted values are (both default to 'Lazy'):
- - \b Lazy: Lazy action management (partial invalidation in lmm +
- heap in action remaining).
- - \b TI: Trace integration. Highly optimized mode when using
- availability traces (only available for the Cas01 CPU model for
- now).
- - \b Full: Full update of remaining and variables. Slow but may be
- useful when debugging.
+configurations.
+ - items \b network/optim and \b CPU/optim (both default to 'Lazy'):
+ - \b Lazy: Lazy action management (partial invalidation in lmm +
+ heap in action remaining).
+ - \b TI: Trace integration. Highly optimized mode when using
+ availability traces (only available for the Cas01 CPU model for
+ now).
+ - \b Full: Full update of remaining and variables. Slow but may be
+ useful when debugging.
+ - items \b network/maxmin_selective_update and
+ \b cpu/maxmin_selective_update: configure whether the underlying
+ should be lazily updated or not. It should have no impact on the
+ computed timings, but should speed up the computation.
+
+It is still possible to disable the \c maxmin_selective_update feature
+because it can reveal counter-productive in very specific scenarios
+where the interaction level is high. In particular, if all your
+communication share a given backbone link, you should disable it:
+without \c maxmin_selective_update, every communications are updated
+at each step through a simple loop over them. With that feature
+enabled, every communications will still get updated in this case
+(because of the dependency induced by the backbone), but through a
+complicated pattern aiming at following the actual dependencies.
+
+\subsection options_model_precision Numerical precision of the platform models
+The analytical models handle a lot of floating point values. It is
+possible to change the epsilon used to update and compare them through
+the \b maxmin/precision item (default value: 1e-9). Changing it
+may speedup the simulation by discarding very small actions, at the
+price of a reduced numerical precision.
\subsection options_model_network Configuring the Network model
-\subsubsection options_model_network_gamma Maximal TCP window size (network/TCP_gamma)
+\subsubsection options_model_network_gamma Maximal TCP window size
The analytical models need to know the maximal TCP window size to take
the TCP congestion mechanism into account. This is set to 20000 by
-default, but can be changed using the network/TCP_gamma variable.
+default, but can be changed using the \b network/TCP_gamma item.
On linux, this value can be retrieved using the following
commands. Both give a set of values, and you should use the last one,
cat /proc/sys/net/ipv4/tcp_wmem # gives the receiver window
\endverbatim
-\subsubsection options_model_network_crosstraffic Simulating cross-traffic (network/crosstraffic)
+\subsubsection options_model_network_coefs Corrective simulation factors
+
+These factors allow to betterly take the slow start into account.
+The corresponding values were computed through data fitting one the
+timings of packet-level simulators. You should not change these values
+unless you are really certain of what you are doing. See
+<a href="http://mescal.imag.fr/membres/arnaud.legrand/articles/simutools09.pdf">Accuracy Study and Improvement of Network Simulation in the SimGrid Framework</a>
+for more informations about these coeficients.
+
+If you are using the SMPI model, these correction coeficients are
+themselves corrected by constant values depending on the size of the
+exchange. Again, only hardcore experts should bother about this fact.
+
+\subsubsection options_model_network_crosstraffic Simulating cross-traffic
As of SimGrid v3.7, cross-traffic effects can be taken into account in
analytical simulations. It means that ongoing and incoming
pair of interconnected hosts. An example of usable platform is
available in <tt>examples/msg/gtnets/crosstraffic-p.xml</tt>.
-This is activated through the \b network/crosstraffic variable, that
-can be set to 0 (disable this feature) or 1 (enable it).
+This is activated through the \b network/crosstraffic item, that
+can be set to 0 (disable this feature) or 1 (enable it).
+
+Note that with the default workstation model this option is activated by default.
+
+\subsubsection options_model_network_coord Coordinated-based network models
+
+When you want to use network coordinates, as it happens when you use
+an \<AS\> in your platform file with \c Vivaldi as a routing, you must
+set the \b network/coordinates to \c yes so that all mandatory
+initialization are done in the simulator.
+
+\subsubsection options_model_network_sendergap Simulating sender gap
+
+(this configuration item is experimental and may change or disapear)
+
+It is possible to specify a timing gap between consecutive emission on
+the same network card through the \b network/sender_gap item. This
+is still under investigation as of writting, and the default value is
+to wait 0 seconds between emissions (no gap applied).
+
+\subsubsection options_pls Configuring packet-level pseudo-models
+
+When using the packet-level pseudo-models, several specific
+configuration flags are provided to configure the associated tools.
+There is by far not enough such SimGrid flags to cover every aspects
+of the associated tools, since we only added the items that we
+needed ourselves. Feel free to request more items (or even better:
+provide patches adding more items).
+
+When using NS3, the only existing item is \b ns3/TcpModel,
+corresponding to the ns3::TcpL4Protocol::SocketType configuration item
+in NS3. The only valid values (enforced on the SimGrid side) are
+'NewReno' or 'Reno' or 'Tahoe'.
+
+When using GTNeTS, two items exist:
+ - \b gtnets/jitter, that is a double value to oscillate
+ the link latency, uniformly in random interval
+ [-latency*gtnets_jitter,latency*gtnets_jitter). It defaults to 0.
+ - \b gtnets/jitter_seed, the positive seed used to reproduce jitted
+ results. Its value must be in [1,1e8] and defaults to 10.
+
+\section options_modelchecking Configuring the Model-Checking
-\section options_modelchecking Model-Checking
-\subsection options_modelchecking_howto How to use it
To enable the experimental SimGrid model-checking support the program should
be executed with the command line argument
\verbatim
void MC_assert(int prop);
\endverbatim
+\section options_virt Configuring the User Process Virtualization
+
+\subsection options_virt_factory Selecting the virtualization factory
+
+In SimGrid, the user code is virtualized in a specific mecanism
+allowing the simulation kernel to control its execution: when a user
+process requires a blocking action (such as sending a message), it is
+interrupted, and only gets released when the simulated clock reaches
+the point where the blocking operation is done.
+
+In SimGrid, the containers in which user processes are virtualized are
+called contexts. Several context factory are provided, and you can
+select the one you want to use with the \b contexts/factory
+configuration item. Some of the following may not exist on your
+machine because of portability issues. In any case, the default one
+should be the most effcient one (please report bugs if the
+auto-detection fails for you). They are sorted here from the slowest
+to the most effient:
+ - \b thread: very slow factory using full featured threads (either
+ ptheads or windows native threads)
+ - \b ucontext: fast factory using System V contexts (or a portability
+ layer of our own on top of Windows fibers)
+ - \b raw: amazingly fast factory using a context switching mecanism
+ of our own, directly implemented in assembly (only available for x86
+ and amd64 platforms for now)
+
+The only reason to change this setting is when the debuging tools get
+fooled by the optimized context factories. Threads are the most
+debugging-friendly contextes.
+
+\subsection options_virt_stacksize Adapting the used stack size
+
+(this only works if you use ucontexts or raw context factories)
+
+Each virtualized used process is executed using a specific system
+stack. The size of this stack has a huge impact on the simulation
+scalability, but its default value is rather large. This is because
+the error messages that you get when the stack size is too small are
+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
+want to reduce the \b contexts/stack_size item. Its default value
+is 128 (in Kib), while our Chord simulation works with stacks as small
+as 16 Kib, for example.
+
+\subsection options_virt_parallel Running user code in parallel
+
+Parallel execution of the user code is only considered stable in
+SimGrid v3.7 and higher. It is described in
+<a href="http://hal.inria.fr/inria-00602216/">INRIA RR-7653</a>.
+
+If you are using the \c ucontext or \c raw context factories, you can
+request to execute the user code in parallel. Several threads are
+launched, each of them handling as much user contexts at each run. To
+actiave this, set the \b contexts/nthreads item to the amount of
+core that you have in your computer.
+
+Even if you asked several worker threads using the previous option,
+you can request to start the parallel execution (and pay the
+associated synchronization costs) only if the potential parallelism is
+large enough. For that, set the \b contexts/parallel_threshold
+item to the minimal amount of user contexts needed to start the
+parallel execution. In any given simulation round, if that amount is
+not reached, the contexts will be run sequentially directly by the
+main thread (thus saving the synchronization costs). Note that this
+option is mainly useful when the grain of the user code is very fine,
+because our synchronization is now very efficient.
+
+When parallel execution is activated, you can choose the
+synchronization schema used with the \b contexts/synchro item,
+which value is either:
+ - \b futex: ultra optimized synchronisation schema, based on futexes
+ (fast user-mode mutexes), and thus only available on Linux systems.
+ This is the default mode when available.
+ - \b posix: slow but portable synchronisation using only POSIX
+ primitives.
+ - \b busy_wait: not really a synchronisation: the worker threads
+ constantly request new contexts to execute. It should be the most
+ efficient synchronisation schema, but it loads all the cores of your
+ machine for no good reason. You probably prefer the other less
+ eager schemas.
+
+\section options_tracing Configuring the tracing subsystem
+
+The \ref tracing "tracing subsystem" can be configured in several
+different ways depending on the nature of the simulator (MSG, SimDag,
+SMPI) and the kind of traces that need to be obtained. See the \ref
+tracing_tracing_options "Tracing Configuration Options subsection" to
+get a detailed description of each configuration option.
+
+We detail here a simple way to get the traces working for you, even if
+you never used the tracing API.
+
+
+- Any SimGrid-based simulator (MSG, SimDag, SMPI, ...) and raw traces:
+\verbatim
+--cfg=tracing:1 --cfg=tracing/uncategorized:1 --cfg=triva/uncategorized:uncat.plist
+\endverbatim
+ The first parameter activates the tracing subsystem, the second
+ tells it to trace host and link utilization (without any
+ categorization) and the third creates a graph configuration file
+ to configure Triva when analysing the resulting trace file.
+
+- MSG or SimDag-based simulator and categorized traces (you need to declare categories and classify your tasks according to them)
+\verbatim
+--cfg=tracing:1 --cfg=tracing/categorized:1 --cfg=triva/categorized:cat.plist
+\endverbatim
+ The first parameter activates the tracing subsystem, the second
+ tells it to trace host and link categorized utilization and the
+ third creates a graph configuration file to configure Triva when
+ analysing the resulting trace file.
+
+- SMPI simulator and traces for a space/time view:
+\verbatim
+smpirun -trace ...
+\endverbatim
+ The <i>-trace</i> parameter for the smpirun script runs the
+simulation with --cfg=tracing:1 and --cfg=tracing/smpi:1. Check the
+smpirun's <i>-help</i> parameter for additional tracing options.
+
+\section options_smpi Configuring SMPI
+
+The SMPI interface provides several specific configuration items.
+These are uneasy to see since the code is usually launched through the
+\c smiprun script directly.
+
+\subsection options_smpi_bench Automatic benchmarking of SMPI code
+
+In SMPI, the sequential code is automatically benchmarked, and these
+computations are automatically reported to the simulator. That is to
+say that if you have a large computation between a \c MPI_Recv() and a
+\c MPI_Send(), SMPI will automatically benchmark the duration of this
+code, and create an execution task within the simulator to take this
+into account. For that, the actual duration is measured on the host
+machine and then scaled to the power of the corresponding simulated
+machine. The variable \b smpi/running_power allows to specify the
+computational power of the host machine (in flop/s) to use when
+scaling the execution times. It defaults to 20000, but you really want
+to update it to get accurate simulation results.
+
+When the code is constituted of numerous consecutive MPI calls, the
+previous mechanism feeds the simulation kernel with numerous tiny
+computations. The \b smpi/cpu_threshold item becomes handy when this
+impacts badly the simulation performance. It specify a threshold (in
+second) under which the execution chunks are not reported to the
+simulation kernel (default value: 1e-6). Please note that in some
+circonstances, this optimization can hinder the simulation accuracy.
+
+\subsection options_smpi_timing Reporting simulation time
+
+Most of the time, you run MPI code through SMPI to compute the time it
+would take to run it on a platform that you don't have. But since the
+code is run through the \c smpirun script, you don't have any control
+on the launcher code, making difficult to report the simulated time
+when the simulation ends. If you set the \b smpi/display_timing item
+to 1, \c smpirun will display this information when the simulation ends. \verbatim
+Simulation time: 1e3 seconds.
+\endverbatim
+
+\section options_generic Configuring other aspects of SimGrid
+
+\subsection options_generic_path XML file inclusion path
+
+It is possible to specify a list of directories to search into for the
+\<include\> tag in XML files by using the \b path configuration
+item. To add several directory to the path, set the configuration
+item several times, as in \verbatim
+--cfg=path:toto --cfg=path:tutu
+\endverbatim
+
+\subsection options_generic_exit Behavior on Ctrl-C
+
+By default, when Ctrl-C is pressed, the status of all existing
+simulated processes is displayed. This is very useful to debug your
+code, but it can reveal troublesome in some cases (such as when the
+amount of processes becomes really big). This behavior is disabled
+when \b verbose-exit is set to 0 (it is to 1 by default).
+
+\section options_index Index of all existing configuration items
+
+- \c contexts/factory: \ref options_virt_factory
+- \c contexts/nthreads: \ref options_virt_parallel
+- \c contexts/parallel_threshold: \ref options_virt_parallel
+- \c contexts/stack_size: \ref options_virt_stacksize
+- \c contexts/synchro: \ref options_virt_parallel
+
+- \c cpu/maxmin_selective_update: \ref options_model_optim
+- \c cpu/model: \ref options_model_select
+- \c cpu/optim: \ref options_model_optim
+
+- \c gtnets/jitter: \ref options_pls
+- \c gtnets/jitter_seed: \ref options_pls
+
+- \c maxmin/precision: \ref options_model_precision
+
+- \c network/bandwidth_factor: \ref options_model_network_coefs
+- \c network/coordinates: \ref options_model_network_coord
+- \c network/crosstraffic: \ref options_model_network_crosstraffic
+- \c network/latency_factor: \ref options_model_network_coefs
+- \c network/maxmin_selective_update: \ref options_model_optim
+- \c network/model: \ref options_model_select
+- \c network/optim: \ref options_model_optim
+- \c network/sender_gap: \ref options_model_network_sendergap
+- \c network/TCP_gamma: \ref options_model_network_gamma
+- \c network/weight_S: \ref options_model_network_coefs
+
+- \c ns3/TcpModel: \ref options_pls
+
+- \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 path: \ref options_generic_path
+- \c verbose-exit: \ref options_generic_exit
+
+- \c workstation/model: \ref options_model_select
+
*/
\ No newline at end of file
