SimGrid  3.9
Versatile Simulation of Distributed Systems
 All Data Structures Functions Variables Typedefs Enumerations Enumerator Groups Pages
Tracing Simulations for Visualization

The trace visualization is widely used to observe and understand the behavior of parallel applications and distributed algorithms. Usually, this is done in a two-step fashion: the user instruments the application and the traces are analyzed after the end of the execution. The visualization itself can highlights unexpected behaviors, bottlenecks and sometimes can be used to correct distributed algorithms. The SimGrid team has instrumented the library in order to let users trace their simulations and analyze them. This part of the user manual explains how the tracing-related features can be enabled and used during the development of simulators using the SimGrid library.

How it works

For now, the SimGrid library is instrumented so users can trace the platform utilization using the MSG, SimDAG and SMPI interface. This means that the tracing will register how much power is used for each host and how much bandwidth is used for each link of the platform. The idea with this type of tracing is to observe the overall view of resources utilization in the first place, especially the identification of bottlenecks, load-balancing among hosts, and so on.

The idea of the tracing facilities is to give SimGrid users to possibility to classify MSG and SimDAG tasks by category, tracing the platform utilization (hosts and links) for each of the categories. For that, the tracing interface enables the declaration of categories and a function to mark a task with a previously declared category. The tasks that are not classified according to a category are not traced. Even if the user does not specify any category, the simulations can still be traced in terms of resource utilization by using a special parameter that is detailed below.

Enabling using CMake

With the sources of SimGrid, it is possible to enable the tracing using the parameter -Denable_tracing=ON when the cmake is executed. The sections Tracing categories functions, Tracing marks functions, and Tracing user variables functions describe all the functions available when this Cmake options is activated. These functions will have no effect if SimGrid is configured without this option (they are wiped-out by the C-preprocessor).

$ cmake -Denable_tracing=ON .
$ make

Tracing categories functions

Tracing marks functions

Tracing user variables functions

For hosts:

For links:

For links, but use source and destination to get route:

Tracing configuration Options

To check which tracing options are available for your simulator, you can just run it with the option –help-tracing. These are the options accepted by the tracing system of SimGrid as of today, you can use them by running your simulator with the –cfg= switch:

  • tracing : Safe switch. It activates (or deactivates) the tracing system. No other tracing options take effect if this one is not activated.
    --cfg=tracing:1
    
  • tracing/categorized : It activates the categorized resource utilization tracing. It should be enabled if tracing categories are used by this simulator.
    --cfg=tracing/categorized:1
    
  • tracing/uncategorized : It activates the uncategorized resource utilization tracing. Use it if this simulator do not use tracing categories and resource use have to be traced.
    --cfg=tracing/uncategorized:1
    
  • tracing/filename : A file with this name will be created to register the simulation. The file is in the Paje format and can be analyzed using Triva or Paje visualization tools. More information can be found in these webpages: http://triva.gforge.inria.fr/ http://paje.sourceforge.net/
    --cfg=tracing/filename:mytracefile.trace
    
    If you do not provide this parameter, the trace file will be named simgrid.trace.
  • tracing/onelink_only : By default, the tracing system uses all routes in the platform file to re-create a "graph" of the platform and register it in the trace file. This option let the user tell the tracing system to use only the routes that are composed with just one link.
    --cfg=tracing/onelink_only:1
    
  • tracing/smpi : This option only has effect if this simulator is SMPI-based. Traces the MPI interface and generates a trace that can be analyzed using Gantt-like visualizations. Every MPI function (implemented by SMPI) is transformed in a state, and point-to-point communications can be analyzed with arrows.
    --cfg=tracing/smpi:1
    
  • tracing/smpi/group : This option only has effect if this simulator is SMPI-based. The processes are grouped by the hosts where they were executed.
    --cfg=tracing/smpi/group:1
    
  • tracing/msg/process : This option only has effect if this simulator is MSG-based. It traces the behavior of all categorized MSG processes, grouping them by hosts. This option can be used to track process location if this simulator has process migration.
    --cfg=tracing/msg/process:1
    
  • tracing/buffer : This option put some events in a time-ordered buffer using the insertion sort algorithm. The process of acquiring and releasing locks to access this buffer and the cost of the sorting algorithm make this process slow. The simulator performance can be severely impacted if this option is activated, but you are sure to get a trace file with events sorted.
    --cfg=tracing/buffer:1
    
  • tracing/onelink_only : This option changes the way SimGrid register its platform on the trace file. Normally, the tracing considers all routes (no matter their size) on the platform file to re-create the resource topology. If this option is activated, only the routes with one link are used to register the topology within an AS. Routes among AS continue to be traced as usual.
    --cfg=tracing/onelink_only:1
    
  • tracing/disable_destroy : Disable the destruction of containers at the end of simulation. This can be used with simulators that have a different notion of time (different from the simulated time).
    --cfg=tracing/disable_destroy:1
    
  • tracing/basic : Some visualization tools are not able to parse correctly the Paje file format. Use this option if you are using one of these tools to visualize the simulation trace. Keep in mind that the trace might be incomplete, without all the information that would be registered otherwise.
    --cfg=tracing/basic:1
    
  • tracing/comment : Use this to add a comment line to the top of the trace file.
    --cfg=tracing/comment:my_string
    
  • tracing/comment_file : Use this to add the contents of a file to the top of the trace file as comment.
    --cfg=tracing/comment_file:textual_file.txt
    
  • triva/categorized : This option generates a graph configuration file for Triva considering categorized resource utilization.
    --cfg=triva/categorized:graph_categorized.plist
    
  • triva/uncategorized : This option generates a graph configuration file for Triva considering uncategorized resource utilization.
    --cfg=triva/uncategorized:graph_uncategorized.plist
    

Case studies

Some scenarios that might help you decide which tracing options you should use to analyze your simulator.

  • I want to trace the resource utilization of all hosts and links of the platform, and my simulator does not use the tracing API. For that, you can run a uncategorized trace with the following parameters (it will work with any Simgrid simulator):
    ./your_simulator \
              --cfg=tracing:1 \
              --cfg=tracing/uncategorized:1 \
              --cfg=tracing/filename:mytracefile.trace \
              --cfg=triva/uncategorized:uncat.plist
    
  • I want to trace only a subset of my MSG (or SimDAG) tasks. For that, you will need to create tracing categories using the TRACE_category (...) function (as explained above), and then classify your tasks to a previously declared category using the MSG_task_set_category (...) (or SD_task_set_category (...) for SimDAG tasks). After recompiling, run your simulator with the following parameters:
    ./your_simulator \
              --cfg=tracing:1 \
              --cfg=tracing/categorized:1 \
              --cfg=tracing/filename:mytracefile.trace \
              --cfg=triva/categorized:cat.plist
    

Example of Instrumentation

A simplified example using the tracing mandatory functions.

int main (int argc, char **argv)
{
  MSG_init (&argc, &argv);

  //(... after deployment ...)

  //note that category declaration must be called after MSG_create_environment
  TRACE_category_with_color ("request", "1 0 0");
  TRACE_category_with_color ("computation", "0.3 1 0.4");
  TRACE_category ("finalize");

  msg_task_t req1 = MSG_task_create("1st_request_task", 10, 10, NULL);
  msg_task_t req2 = MSG_task_create("2nd_request_task", 10, 10, NULL);
  msg_task_t req3 = MSG_task_create("3rd_request_task", 10, 10, NULL);
  msg_task_t req4 = MSG_task_create("4th_request_task", 10, 10, NULL);
  MSG_task_set_category (req1, "request");
  MSG_task_set_category (req2, "request");
  MSG_task_set_category (req3, "request");
  MSG_task_set_category (req4, "request");

  msg_task_t comp = MSG_task_create ("comp_task", 100, 100, NULL);
  MSG_task_set_category (comp, "computation");

  msg_task_t finalize = MSG_task_create ("finalize", 0, 0, NULL);
  MSG_task_set_category (finalize, "finalize");

  //(...)

  MSG_clean();
  return 0;
}

Analyzing the SimGrid Traces

The SimGrid library, during an instrumented simulation, creates a trace file in the Paje file format that contains the platform utilization for the simulation that was executed. The visualization analysis of this file is performed with the visualization tool Triva, with special configurations tunned to SimGrid needs. This part of the documentation explains how to configure and use Triva to analyse a SimGrid trace file.

  • Installing Triva: the tool is available in the Inria's Forge, at http://triva.gforge.inria.fr. Use the following command to get the sources, and then check the file INSTALL. This file contains instructions to install the tool's dependencies in a Ubuntu/Debian Linux. The tool can also be compiled in MacOSX natively, check INSTALL.mac file.
    $ git clone git://scm.gforge.inria.fr/triva/triva.git
    $ cd triva
    $ cat INSTALL
    
  • Executing Triva: a binary called Triva is available after the installation (you can execute it passing –help to check its options). If the triva binary is not available after following the installation instructions, you may want to execute the following command to initialize the GNUstep environment variables. We strongly recommend that you use the latest GNUstep packages, and not the packages available through apt-get in Ubuntu/Debian packaging systems. If you install GNUstep using the latest available packages, you can execute this command:
    $ source /usr/GNUstep/System/Library/Makefiles/GNUstep.sh
    
    You should be able to see this output after the installation of triva:
    $ ./Triva.app/Triva --help
    Usage: Triva [OPTIONS...] TRACE0 [TRACE1]
    Trace Analysis through Visualization
    
    TimeInterval
        --ti_frequency {double}    Animation: frequency of updates
        --ti_hide                  Hide the TimeInterval window
        --ti_forward {double}      Animation: value to move time-slice
        --ti_apply                 Apply the configuration
        --ti_update                Update on slider change
        --ti_animate               Start animation
        --ti_start {double}        Start of time slice
        --ti_size {double}         Size of time slice
    Triva
        --comparison               Compare Trace Files (Experimental)
        --graph                    Configurable Graph
        --list                     Print Trace Type Hierarchy
        --hierarchy                Export Trace Type Hierarchy (dot)
        --stat                     Trace Statistics and Memory Utilization
        --instances                List All Trace Entities
        --linkview                 Link View (Experimental)
        --treemap                  Squarified Treemap
        --merge                    Merge Trace Files (Experimental)
        --check                    Check Trace File Integrity
    GraphConfiguration
        --gc_conf {file}           Graph Configuration in Property List Format
        --gc_apply                 Apply the configuration
        --gc_hide                  Hide the GraphConfiguration window
    
    Triva expects that the user choose one of the available options (currently –graph or –treemap for a visualization analysis) and the trace file from the simulation.
  • Understanding Triva - time-slice: the analysis of a trace file using the tool always takes into account the concept of the time-slice. This concept means that what is being visualized in the screen is always calculated considering a specific time frame, with its beggining and end timestamp. The time-slice is configured by the user and can be changed dynamically through the window called Time Interval that is opened whenever a trace file is being analyzed. The next figure depicts the time-slice configuration window. In the top of the window, in the space named Trace Time, the two fields show the beggining of the trace (which usually starts in 0) and the end (that depends on the time simulated by SimGrid). The middle of the window, in the square named Time Slice Configuration, contains the aspects related to the time-slice, including its start and its size. The gray rectangle in the bottom of this part indicates the current time-slice that is considered for the drawings. If the checkbox Update Drawings on Sliders Change is not selected, the button Apply must be clicked in order to inform triva that the new time-slice must be considered. The bottom part of the window, in the space indicated by the square Time Slice Animation can be used to advance the time-frame automatically. The user configures the amount of time that the time-frame will forward and how frequent this update will happen. Once this is configured, the user clicks the Play button in order to see the dynamic changes on the drawings.
    Remarks: when the trace has too many hosts or links, the computation to take into account a new time-slice can be expensive. When this happens, the Frequency parameter, but also updates caused by change on configurations when the checkbox Update Drawings on Sliders Change is selected will not be followed.
  • Understanding Triva - graph: one possibility to analyze SimGrid traces is to use Triva's graph view, using the –graph parameter to activate this view, and –gc_conf with a graph configuration to customize the graph according to the traces. A valid graph configuration (we are using the non-XML Property List Format to describe the configuration) can be created for any SimGrid-based simulator using the –cfg=triva/uncategorized:graph_uncategorized.plist or –cfg=triva/categorized:graph_categorized.plist (if the simulator defines resource utilization categories) when executing the simulation.

Basic SimGrid Configuration: The basic description of the configuration is as follows:

{
  node = (LINK, HOST, );
  edge = (HOST-LINK, LINK-HOST, LINK-LINK, );

The nodes of the graph will be created based on the node parameter, which in this case is the different "HOST"s and "LINK"s of the platform used to simulate. The edge parameter indicates that the edges of the graph will be created based on the "HOST-LINK"s, "LINK-HOST"s, and "LINK-LINK"s of the platform. After the definition of these two parameters, the configuration must detail how the nodes (HOSTs and LINKs) should be drawn.

For that, the configuration must have an entry for each of the types used. For HOST, as basic configuration, we have:

  HOST = {
    type = square;
    size = power;
    values = (power_used);
  };

The parameter size indicates which variable from the trace file will be used to define the size of the node HOST in the visualization. If the simulation was executed with availability traces, the size of the nodes will be changed according to these traces. The parameter type indicates which geometrical shape will be used to represent HOST, and the values parameter indicates which values from the trace will be used to fill the shape.

For LINK we have:

  LINK = {
    type = rhombus;
    size = bandwidth;
    values = (bandwidth_used);
  };
}

The same configuration parameters are used here: type (with a rhombus), the size (whose value is from trace's bandwidth variable) and the values.

Customizing the Graph Representation: triva is capable to handle a customized graph representation based on the variables present in the trace file. In the case of SimGrid, every time a category is created for tasks, two variables in the trace file are defined: one to indicate node utilization (how much power was used by that task category), and another to indicate link utilization (how much bandwidth was used by that category). For instance, if the user declares a category named request, there will be variables named prequest and a brequest (p for power and b for bandwidth). It is important to notice that the variable prequest in this case is only available for HOST, and brequest is only available for LINK. Example: suppose there are two categories for tasks: request and compute. To create a customized graph representation with a proportional separation of host and link utilization, use as configuration for HOST and LINK this:

  HOST = {
    type = square;
    size = power;
    values = (prequest, pcomputation);
  };
  LINK = {
    type = rhombus;
    size = bandwidth;
    values = (brequest, bcomputation);
  };

This configuration enables the analysis of resource utilization by MSG tasks, and the identification of load-balancing issues, network bottlenecks, for instance.

The Graph Visualization: The next figure shows a graph visualization of a given time-slice of the masterslave_forwarder example (present in the SimGrid sources). The red color indicates tasks from the compute category. This visualization was generated with the following configuration:

{
  node = (LINK, HOST, );
  edge = (HOST-LINK, LINK-HOST, LINK-LINK, );

  host = {
    type = square;
    size = power;
    values = (pcompute, pfinalize);
  };
  link = {
    type = rhombus;
    size = bandwidth;
    values = (bcompute, bfinalize);
  };
}
  • Understading Triva - colors: Colors are now registered in trace files. See the tracing API to how to define them for your simulator.