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.. _TUT-RM: Runtime Model ************* Using FleCSI requires proper initialization and configuration of the FleCSI runtime. These examples illustrate some of the basic steps and options that are available. ---- Example 1: Minimal ++++++++++++++++++ The core FleCSI runtime has three control points: *initialize*, *start*, and *finalize*. These must be invoked by the user's application code in that order. .. sidebar:: Top-level Action The top-level action is a C++ function created by the user to tell FleCSI what it should do when the *start* control point is invoked. * **initialize** |br| This control point spins up the FleCSI runtime and (optionally) any other runtimes on which FleCSI depends. * **start** |br| This control point begins the actual runtime execution that forms the bulk of any simulation that is performed using FleCSI. The user must pass a top-level action that FleCSI will execute. * **finalize** |br| This control point shuts down the FleCSI runtime and any other runtimes that FleCSI itself initialized. This example demonstrates a minimal use of FleCSI that just executes an action to print out *Hello World*. Code for this example can be found in *tutorial/1-runtime/1-minimal.cc*. .. literalinclude:: ../../../../tutorial/1-runtime/1-minimal.cc :language: cpp .. note:: - The top-level action can be any C/C++ function that takes no arguments and returns an int. In this simple example, we only print a message to indicate that the top-level action was actually executed by FleCSI. However, in a real application, the top-level action would execute FleCSI tasks and other functions to implement the simulation. - The main function must invoke initialize, start, and finalize on the FleCSI runtime. Otherwise, the implementation of main is left to the user. - The status returned by FleCSI's initialize method should be inspected to see if the end-user specified --help on the command line. FleCSI has built-in command-line support using Boost Program Options. This is documented in the next example. ---- Example 2: Program Options ++++++++++++++++++++++++++ FleCSI supports a program options capability based on `Boost Program Options`__ to simplify the creation and management of user-defined command-line options. The basic syntax for adding and accessing program options is semantically similar to the Boost interface (You can find documentation using the above link.) However, there are some notable differences: * FleCSI internally manages the boost::program_options::value variables for you, using boost::optional. * Positional options are the mechanism that should be used for *required* options. * Default, implicit, zero, and multi value attributes are specified in the flecsi::program_option constructor as an std::initializer_list. This section of the tutorial provides examples of how to use FleCSI's program option capability. __ https://www.boost.org/doc/libs/1_63_0/doc/html/program_options.html Example Program ^^^^^^^^^^^^^^^ In this example, imagine that you have a program that takes information about a taxi service (The options are silly and synthetic. However they demonstrate the basic usage of the flecsi::program_option type.) The command-line options and arguments for the program allow specification of the following: trim level, transmission, child seat, purpose (personal or business), light speed, and a passenger list. The first two options will be in a *Car Options* section, while the purpose will be under the *Ride Options* section. The passenger list is a positional argument to the program. The help output for the entire program looks like this: .. code-block:: console Usage: runtime-program_options Positional Options: passenger-list The list of passengers for this trip [.txt]. Basic Options: -h [ --help ] Print this message and exit. Car Options: -l [ --level ] arg (= 1) Specify the trim level [1-10]. -t [ --transmission ] arg (= manual) Specify the transmission type ["automatic", "manual"]. -c [ --child-seat ] [=arg(= 1)] (= 0) Request a child seat. Ride Options: -p [ --purpose ] arg (= 1) Specify the purpose of the trip (personal=0, business=1). --lightspeed Travel at the speed of light. FleCSI Options: --backend-args arg Pass arguments to the backend. The single argument is a quoted string of backend-specific options. --flog-tags arg (=all) Enable the specified output tags, e.g., --flog-tags=tag1,tag2. Use '--flog-tags=all' to show all output, and '--flog-tags=unscoped' to show only unguarded output. --flog-verbose [=arg(=1)] (=0) Enable verbose output. Passing '-1' will strip any additional decorations added by flog and will only output the user's message. --flog-process arg (=0) Restrict output to the specified process id. The default is process 0. Use '--flog-process=-1' to enable all processes. This shows the program usage, the basic options, e.g., ``--help``, the command-line and positional options for the example, and some auxiliary options for controlling the FleCSI logging utility *FLOG* (described in the next section of this tutorial). The FLOG options will only appear if *ENABLE_FLOG=ON* was set in your FleCSI build. Declaring Options ^^^^^^^^^^^^^^^^^ .. note:: FleCSI program options must be declared at namespace scope, i.e., outside of any function, class, or enum class. This is not a problem! It is often convenient to declare them in a header file (in which case, they must also be declared *inline*) or directly before the *main* function. We use the latter for this example simply for conciseness. Let's consider the first *Car Options* option: ``--level``. To declare this option, we use the following declaration: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add an integer-valued command-line option with a default value :end-before: // Add a string-valued command-line option with a default value First, notice that the flecsi::program_option type is templated on the underlying option type *int*. In general, this can be any valid C++ type. This constructor to flecsi::program_option takes the following parameters: * *section ("Car Options")*: |br| Identifies the section. Sections are generated automatically, simply by referencing them in a program option. * *flag ("level,l")*: |br| The long and short forms of the option. If the string contains a comma, it is split into *long name,short name*. If there is no comma, the string is used as the long name with no short name. * *help ("Specify...")* |br| The help description that will be displayed when the usage message is printed. * *values ({{flecsi::option_default, ...}})* |br| This is a std::initializer_list>. The possible values are flecsi::option_default, flecsi::option_implicit, flecsi::option_zero, and flecsi::option_multi. The default value is used if the option is not passed at invocation. The implicit value is used if the option is passed without a value. If zero is specified, the option does not take an argument, and an implicit value must be provided. If multi is specified, the option takes multiple values. * *check ([](flecsi::any const &, std::stringstream & ss...)* |br| An optional, user-defined predicate to validate the value passed by the user. The next option ``--transmission`` is similar but uses a ``std::string`` value type: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add a string-valued command-line option with a default value :end-before: // Add an option that defines an implicit value. The only real difference is that (because the underlying type is std::string) the default value is also a string. The last option in the "Car Options" section ``--child-seat`` demonstrates the use of flecsi::option_implicit: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add an option that defines an implicit value. :end-before: // Add a an option to a different section, Providing an implicit value defines the behavior for the case that the user invokes the program with the given flag but does not assign a value, e.g., ``--child-seat`` vs. ``--child-seat=1``. The value is *implied* by the flag itself. .. caution:: This style of option should not be used with positional arguments because Boost appears to have a bug when such options are invoked directly before a positional option (gets confused about separation). We break that convention here for the sake of completeness. If you need an option that simply acts as a switch (i.e., it is either *on* or *off*), consider using the ``--lightspeed`` style option below, as this type of option is safe to use with positional options. The first option in the *Ride Options* section ``--purpose`` takes an integer value *0* or *1*. This option is declared with the following code: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add a an option to a different section, :end-before: // Add an option with no default. This option demonstrates how an enumeration can be used to define possible values. Although FleCSI does not enforce correctness, the enumeration can be used to check that the user-provided value is valid. The next option in the *Ride Options* section ``--lightspeed`` defines an implicit value and zero values (meaning that it takes no values). The ``--lightspeed`` option acts as a switch, taking the implicit value if the flag is passed. This will be useful to demonstrate how we can check whether or not an option was passed in the next section: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add an option with no default. :end-before: // Add a positional option. The final option in this example is a positional option: i.e., it is an argument to the program itself. .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add a positional option. :end-before: // User-defined program options are available after FleCSI Positional options are required: i.e., the program will error and print the usage message if a value is not passed. Checking & Using Options ^^^^^^^^^^^^^^^^^^^^^^^^ FleCSI option variables are implemented using an *optional* C++ type. The utility of this implementation is that *optional* already captures the behavior that we want from an option (i.e., it either has a value or does not). If the option has a value, the specific value depends on whether or not the user explicitly passed the option on the command line and on its default and implicit values. Options that have a default value defined do not need to be tested: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add cost for trim level. :end-before: // Add cost for lightspeed. Here, we simply need to access the value of the option using the *value()* method. For options with no default value, we can check whether or not the option has a value using the *has_value()* method: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Add cost for lightspeed. :end-before: // Do something with the positional argument. Our one positional option works like the defaulted options (because it is required) and can be accessed using the *value()* method: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp :start-at: // Do something with the positional argument. :end-at: price *= passengers * 1.10 * price; Here is the full source for this tutorial example: .. literalinclude:: ../../../../tutorial/1-runtime/2-program_options.cc :language: cpp ---- Example 3: FLOG (FleCSI Logging Utility) ++++++++++++++++++++++++++++++++++++++++ FLOG provides users with a mechanism to print logging information to various stream buffers, similar to the C++ objects std::cout, std::cerr, and std::clog. Multiple streams can be used simultaneously, so that information about the running state of a program can be captured and displayed at the same time. In this example, we show how FLOG can be configured to stream output to a file buffer and the ``std::clog`` stream buffer. Before attempting this example, you should make sure that you have configured and built FleCSI with ENABLE_FLOG=ON. .. important:: One of the challenges of using distributed-memory and tasking runtimes is that output written to the console often collide because multiple threads of execution are all writing to the same descriptor concurrently. FLOG fixes this by collecting output from different threads and serializing it. This is an important and useful feature of FLOG. Buffer Configuration ^^^^^^^^^^^^^^^^^^^^ By default, FLOG does not produce any output (even when enabled). In order to see or capture output, your application must add at least one output stream. This should be done after ``flecsi::initialize`` has been invoked and before flecsi::start. Consider the main function for this example: .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-after: // top_level_action :end-at: } // main The first output stream added is `std::clog`__. __ https://en.cppreference.com/w/cpp/io/clog .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-at: // Add the standard log descriptor to FLOG's buffers. :end-at: log::add_output_stream("clog", std::clog, true); The arguments to add_output_stream are: * *label ("clog")*: |br| This is an arbitrary label that may be used in future versions to enable or disable output. The label should be unique. * *stream buffer (std::clog)*: |br| A std::ostream object. * *colorize (true)*: |br| A boolean indicating whether or not output to this stream buffer should be colorized. It is useful to turn off colorization for non-interactive output. The default is *false*. To add an output stream to a file, we can do the following: .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-at: // Add an output file to FLOG's buffers. :end-at: log::add_output_stream("log file", log_file); That's it! For this example, FLOG is now configured to write output to std::clog, and to *output.txt*. Next, we will see how to actually write output to these stream buffers. Writing to Buffers ^^^^^^^^^^^^^^^^^^ Output with FLOG is similar to std::cout. Consider the FLOG *info* object: .. code-block:: cpp flog(info) << "The value is " << value << std::endl; This works just like any of the C++ output objects. FLOG provides four basic output objects: *trace*, *info*, *warn*, and *error*. These provide different color decorations for easy identification in terminal output and can be controlled using *strip levels* (discussed in the next section). The following code from this example shows some trivial usage of each of the basic output objects: .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-at: // This output will always be generated because :end-at: flog(error) << "Error level output" << std::endl; Controlling Output - Strip Levels ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. important:: If FleCSI is configured with ENABLE_FLOG=OFF, all FLOG calls are compiled out: i.e., there is no runtime overhead. The strip level is a preprocessor option *FLOG_STRIP_LEVEL* that can be specified during FleCSI configuration. Valid strip levels are *[0-4]*. The default strip level is *0* (most verbose). Depending on the strip level, FLOG limits the type of messages that are output. * *trace* |br| Output written to the trace object is enabled for strip levels less than 1. * *info* |br| Output written to the info object is enabled for strip levels less than 2. * *warn* |br| Output written to the warn object is enabled for strip levels less than 3. * *error* |br| Output written to the error object is enabled for strip levels less than 4. Controlling Output - Tag Groups ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Tag groups provide a mechanism to control the runtime output generated by FLOG. The main idea here is that developers can use FLOG to output information that is useful in developing or debugging a program and leave it in the code. Then, specific groups of messages can be enabled or disabled to only output useful information for the current development focus. To create a new tag, we use the flog::tag type: .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-at: // Create some tags to control output. :end-at: log::tag tag2("tag2"); Tags take a single std::string argument that is used in the help message to identify available tags. .. important:: FLOG tags must be declared at namespace scope. Once you have declared a tag, it can be used to limit output to one or more *scoped* regions. The following code defines a guarded section of output that will only be generated if *tag1* or *all* is specified to the ``--flog-tags`` option: .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-at: // This output will only be generated if 'tag1' or 'all' is specified :end-at: } // scope Here is another code example that defines a guarded section for *tag2*: .. literalinclude:: ../../../../tutorial/1-runtime/3-flog.cc :language: cpp :start-at: // This output will only be generated if 'tag2' or 'all' is specified :end-at: } // scope You should experiment with invoking this example: Invoking this example with the ``--help`` flag will show the available tags: .. code-block:: console $ ./runtime-flog --help which should look something like this: .. code-block:: console Usage: runtime-flog Basic Options: -h [ --help ] Print this message and exit. FleCSI Options: --backend-args arg Pass arguments to the runtime backend. The single argument is a quoted string of backend-specific options. --flog-tags arg (=all) Enable the specified output tags, e.g., --flog-tags=tag1,tag2. Use '--flog-tags=all' to show all output, and '--flog-tags=unscoped' to show only unguarded output. --flog-verbose [=arg(=1)] (=0) Enable verbose output. Passing '-1' will strip any additional decorations added by flog and will only output the user's message. --flog-process arg (=0) Restrict output to the specified process id. The default is process 0. Use '--flog-process=-1' to enable all processes. Available FLOG Tags (FleCSI Logging Utility): tag2 tag1 Invoking this example with ``--flog-tags=tag1`` will generate output for unguarded sections and for output guarded with the *tag1* tag: .. code-block:: console $ ./flog --flog-tags=tag1 [trace all p0] Trace level output [info all p0] Info level output [Warn all p0] Warn level output [ERROR all p0] Error level output [trace tag1 p0] Trace level output (in tag1 guard) [info tag1 p0] Info level output (in tag1 guard) [Warn tag1 p0] Warn level output (in tag1 guard) [ERROR tag1 p0] Error level output (in tag1 guard) FLOG Options (CMake) ^^^^^^^^^^^^^^^^^^^^ Defaults for the FLOG options have been chosen in an attempt to most closely model the behavior one would expect from the execution and output of a standard MPI program. However, because of the asynchronous nature of FleCSI's execution model, it is important to understand the options that control FLOG's behavior, as it can sometimes be counter-intuitive. As stated in the preceding sections, FLOG buffers and serializes output to avoid collisions from different threads. As a safeguard, FleCSI's default settings flush these buffers periodically, so as to avoid memory capacity issues. The CMake configuration option ``FLOG_SERIALIZATION_INTERVAL`` defines this behavior: * *FLOG_SERIALIZATION_INTERVAL* |br| The serialization interval specifies how often FleCSI should check for buffered output (requires reduction) as a number of tasks executed: i.e., if the serialization interval is set to 300, FleCSI will check how many messages have been injected into the stream of each process every multiple of 300 task executions. |br| *(default: 100)* .. caution:: It is important to understand and tune FLOG serialization to your application. Serialization inhibits task asynchrony. When balanced, the performance effects should be very minimal. However, overly aggressive settings, e.g., ``FLOG_SERIALIZATION_INTERVAL=1`` could force complete serialization of your application. This can be beneficial for debugging, but should not be used for actual simulation runs. For many applications, there is a natural serialization interval that implicitly starts at the beginning of the simulation time evolution. FleCSI provides a function ``flecsi::flog::flush()`` that can be used to force FleCSI to serialize and flush output. .. tip:: Best practice for FLOG serialization is to leave the default settings for ``FLOG_SERIALIZATION_INTERVAL`` and to use ``flecsi::flog::flush()`` at an appropriate point in your application to force output. FLOG Options (Command-Line) ^^^^^^^^^^^^^^^^^^^^^^^^^^^ We have already covered the ``--flog-tags`` option. There are currently two other options that control FLOG output: * *--flog-verbose* |br| This option controls how much additional information is output with your ``flog(severity)`` message. A value of ``-1`` will turn off any additional decorations, while a value of ``1`` will add additional information. By default, the severity level and process are output. |br| *(default: 0)* * *--flog-process* |br| This options allows the user to restrict output to the specified process id. A value of ``-1`` will enable output of all processes. By default, output is restricted to process ``0``. |br| *(default: 0)* .. caution:: By default, FLOG only writes output to process ``0``. Pass ``--flog-process=-1`` to enable output from all processes. .. tip:: Logging output can sometimes have unexpected behavior. Consider the case where you are viewing output only from process ``0`` and the runtime maps a task to process ``1``. You will not see the messages from that task in the logging output. This is not an error. In general, some experimentation is necessary to achieve the desired level of output with FLOG and FleCSI. Example 4: Caliper Annotations ++++++++++++++++++++++++++++++ The `Caliper `_ Annotation interface in FleCSI is used internally to inject Caliper instrumentation throughout the code. This enables users to investigate runtime overhead and application performance with Caliper. Users can also use this interface to add additional annotations to performance sensitive regions of their applications. To CMake variable *CALIPER_DETAIL* is used to disable or control the level of detail in included Caliper annotations. The currently available options are: * *CALIPER_DETAIL=none* |br| Caliper annotations are disabled * *CALIPER_DETAIL=low* |br| Annotations marked with low severity detail are included * *CALIPER_DETAIL=medium* |br| Annotations marked with low and medium severity detail are included * *CALIPER_DETAIL=high* |br| All annotations are included .. caution:: To use Caliper annotations with the Legion backend, the Legion option ``-ll:force_kthreads`` must be used. Caliper is not aware of Legion user-level threads, so additional care must be practiced when using annotations with this runtime. Adding Annotations ^^^^^^^^^^^^^^^^^^ In addition to instrumenting FleCSI runtime overhead, the annotation interface can be used to add annotations to applications. This allows users to instrument their code and use Caliper to collect timing data. An annotation for a code region must specify a detail level, context, and name. The detail level is used to selectively control the inclusion of an annotation using the cmake variable *CALIPER_DETAIL*. The context for an annotation is used as a named grouping for annotations. In caliper, this can be used to filter and aggregate annotations using the `caliper query language `_. Scope guards are used to annotate a code region. Consider the main function for this example: .. literalinclude:: ../../../../tutorial/1-runtime/4-caliper.cc :language: cpp :start-after: // main :end-at: } // main A scope guard is used to annotate the top level task: .. literalinclude:: ../../../../tutorial/1-runtime/4-caliper.cc :language: cpp :start-at: status = (annotation::guard( :end-at: flecsi::start(top_level_action)); For this region, the FleCSI execution context ``annotation::execution`` is specified along with a detail level of ``annnotation::detail::low``. To avoid hard coding strings throughout an application, annotation regions can be specified using structs that inherit from ``annotation::region``: .. literalinclude:: ../../../../tutorial/1-runtime/4-caliper.cc :language: cpp :start-at: struct user_execution : annotation::context { :end-before: void This first defines a new annotation context ``user_execution`` by inheriting from ``annotation::context`` and specifying a name for the context. Three code regions are then defined using this context. The first two regions use the default detail level of ``annotation::detail::medium``. The main and sleeper functions are then annotated using region-based scope guards: .. literalinclude:: ../../../../tutorial/1-runtime/4-caliper.cc :language: cpp :start-at: annotation::rguard main_guard; :end-at: annotation::rguard main_guard; .. literalinclude:: ../../../../tutorial/1-runtime/4-caliper.cc :language: cpp :start-at: annotation::rguard(), :end-at: std::this_thread::sleep_for(std::chrono::milliseconds(400)); Generating Reports ^^^^^^^^^^^^^^^^^^ `Caliper configuration files `_ can be used to generate configure caliper to generate reports for annotated regions of the code. For example, consider the following caliper configuration file: .. literalinclude:: ../../../../tutorial/1-runtime/caliper.config :language: bash This file defines three caliper configuration profiles that can be used to generate reports using the ``mpireport`` service (see http://software.llnl.gov/Caliper/services.html). This service aggregates timings across all ranks using ``CALI_MPI_REPORT_CONFIG`` query statements. For example, to run with the second configuration profile in this file (named user), ensure ``caliper.config`` is in your working directory and run with:: CALI_CONFIG_PROFILE=user ./runtime-caliper When the program completes, caliper flushes the aggregated timings to a report file named ``report.cali``:: User-Execution count min-time max-time total-time-% sleeper/subtask 1 0.400095 0.400095 57.141409 sleeper 2 0.300089 0.300089 42.858591 The output represents collected timings for annotations in the ``User-Execution`` annotation context. .. vim: set tabstop=2 shiftwidth=2 expandtab fo=cqt tw=72 :