Caliper Basics

Caliper is a library to integrate performance profiling capabilities into applications. To use Caliper, developers mark code regions of interest using Caliper’s annotation API. Applications can then enable performance profiling at runtime with Caliper’s configuration API. Alternatively, you can configure Caliper through environment variables or config files.

This tutorial covers basic Caliper usage, including source-code annotations and using Caliper’s built-in performance measurement configurations. Most of the examples shown here use the cxx-example program in the Caliper Git repository. There is a complete listing at the end of this tutorial: C++ example program.

Build and install

You can install Caliper with Spack, or clone it directly from Github:

$ git clone

Caliper uses CMake and C++11. To build it, run cmake:

$ mkdir build && cd build
$ cmake ..
$ make && make install

There are many build flags to enable optional features, such as -DWITH_MPI for MPI support. See Building Caliper for details.

Caliper installs files into the lib64, include, and bin directories under CMAKE_INSTALL_PREFIX. To use Caliper, link libcaliper to the target program:

$ g++ -o app app.o -L<path to caliper installation>/lib64 -lcaliper

Caliper provides the caliper CMake target, which can be used to add a dependency on Caliper in CMake:

add_executable(MyExample MyExample.cpp)
target_link_libraries(MyExample PRIVATE caliper)

When configuring the target program, point CMake to the desired Caliper installation with caliper_DIR:

cmake -Dcaliper_DIR=<caliper-installation-dir>/share/cmake/caliper ..

Region profiling

Caliper’s source-code annotation API allows you to mark source-code regions of interest in your program. Much of Caliper’s functionality depends on these region annotations.

Caliper provides macros and functions for C, C++, and Fortran to mark functions, loops, or sections of source-code. For example, use CALI_CXX_MARK_FUNCTION to mark a function in C++:

#include <caliper/cali.h>

void foo()
    // ...

You can mark arbitrary code regions with the CALI_MARK_BEGIN and CALI_MARK_END macros or the corresponding cali_begin_region() and cali_end_region() functions:

#include <caliper/cali.h>

// ...
CALI_MARK_BEGIN("my region");
// ...
CALI_MARK_END("my region");

You can have as many regions as you like. Regions can be nested, but they must be stacked properly, i.e. the name in an end region call must match the current innermost open region. For more details, including C and Fortran examples, refer to the annotation API reference: Annotation API reference.

With the source-code annotations in place, we can run performance measurements. By default, Caliper does not record data - we have to activate performance profiling at runtime. An easy way to do this is to use one of Caliper’s built-in measurement configurations. For example, the runtime-report config prints out the time spent in the annotated regions. You can activate built-in measurement configurations with the ConfigManager API or with the CALI_CONFIG environment variable. Let’s try this on Caliper’s cxx-example program:

$ cd Caliper/build
$ make cxx-example
$ CALI_CONFIG=runtime-report ./examples/apps/cxx-example
Path       Min time/rank Max time/rank Avg time/rank Time %
main            0.000119      0.000119      0.000119  7.079120
  mainloop      0.000067      0.000067      0.000067  3.985723
    foo         0.000646      0.000646      0.000646 38.429506
  init          0.000017      0.000017      0.000017  1.011303

Like most built-in configurations, the runtime-report config works for MPI and non-MPI programs. By default, it reports the minimum, maximum, and average exclusive time (seconds) spent in each marked code region across MPI ranks (the three values are identical in non-MPI programs). Exclusive time is the time spent in a region without the time spent in its children.

You can customize the report with additional options. Some options enable additional Caliper functionality, such as profiling MPI and CUDA functions in addition to the user-defined regions, or additional metrics like memory usage. Another example is the calc.inclusive option, which prints inclusive instead of exclusive region times:

$ CALI_CONFIG=runtime-report,calc.inclusive ./examples/apps/cxx-example
Path       Min time/rank Max time/rank Avg time/rank Time %
main            0.000658      0.000658      0.000658 55.247691
  mainloop      0.000637      0.000637      0.000637 53.484467
    foo         0.000624      0.000624      0.000624 52.392947
  init          0.000003      0.000003      0.000003  0.251889

Caliper provides many more performance measurement configurations in addition to runtime-report that make use of region annotations. For example, hatchet-region-profile writes a json file with region times for processing with Hatchet. See More on configurations below to learn more about different configurations and their options.

Notes on multi-threading

Some care must be taken when annotating multi-threaded programs. Regions are either visible only on the thread that creates them, or shared by all threads. You can set the visibility scope (thread or process) with the CALI_CALIPER_ATTRIBUTE_DEFAULT_SCOPE configuration variable. It is set to thread by default.

A common practice is to mark code regions only on the master thread, outside of multi-threaded regions. In this case, it is useful to set the visibility scope to process:

#include <caliper/cali.h>

int main()
    cali_config_set("CALI_CALIPER_ATTRIBUTE_DEFAULT_SCOPE", "process");


#pragma omp parallel
        // ...


The annotation placement inside or outside of threads also affects performance measurements: in event-based measurement configurations (e.g., runtime-report), measurements are taken when entering and exiting annotated regions. Therefore, in the example above, the reported performance metrics (such as time per region) are only for the master thread. However, sampling-based configurations like callpath-sample-report can take measurements on all threads, regardless of region markers. The process visibility scope then allows us to associate these measurements with the “parallel” and “main” regions on any thread.

In contrast, in the example below, we enter and exit the “parallel” region on every thread, and metrics reported by runtime-report therefore cover all threads. However, the “main” region is only visible on the master thread.

#include <caliper/cali.h>

int main()

#pragma omp parallel
        // ...


ConfigManager API

A distinctive Caliper feature is the ability to enable performance measurements programmatically with the ConfigManager API. For example, we often let users activate performance measurements with a command-line argument.

The ConfigManager API provides access to Caliper’s built-in measurement configurations (see More on configurations below). The ConfigManager interprets a short configuration string that can be hard-coded in the program or provided by the user in some form, e.g. as a command-line parameter or in the program’s configuration file.

To access and control the built-in configurations, create a cali::ConfigManager object. Add a configuration string with add(), start the requested configuration channels with start(), and trigger output with flush(). In MPI programs, the flush() method must be called before MPI_Finalize:

#include <caliper/cali.h>
#include <caliper/cali-manager.h>

#include <mpi.h>

#include <iostream>

int main(int argc, char* argv[])
    MPI_Init(&argc, &argv);

    cali::ConfigManager mgr;

    // Check for configuration errors
    if (mgr.error())
        std::cerr << "Caliper error: " << mgr.error_msg() << std::endl;

    // Start configured performance measurements, if any

    // ...

    // Flush output before finalizing MPI


The C++ example program uses the ConfigManager API to let users specify a Caliper configuration with the -P command-line argument, e.g. -P runtime-report:

$ ./examples/apps/cxx-example -P runtime-report
Path       Min time/rank Max time/rank Avg time/rank Time %
main            0.000129      0.000129      0.000129  5.952930
  mainloop      0.000080      0.000080      0.000080  3.691740
    foo         0.000719      0.000719      0.000719 33.179511
  init          0.000021      0.000021      0.000021  0.969082

See ConfigManager API reference for the complete API documentation. The c-example and fortran-example example programs in the Caliper source show how to use the ConfigManager API from C and Fortran, respectively. See More on configurations below for the configuration string syntax.


  • Multiple ConfigManager objects can co-exist in a program.

  • The ConfigManager API can be used in combination with the CALI_CONFIG environment variable or manual configurations.

More on configurations

A configuration string for the ConfigManager API or the CALI_CONFIG environment variable is a comma-separated list of configs and parameters.

A config is the name of one of Caliper’s built-in measurement configurations, e.g. runtime-report. Multiple configs can be specified, separated by comma.

Most configs have optional parameters, e.g. output to name an output file. Parameters can be specified as a list of key-value pairs in parentheses after the config name, e.g. runtime-report(output=report.txt,io.bytes). For boolean parameters, only the key needs to be added to enable it; for example, io.bytes is equal to io.bytes=true. You can also add parameters outside of parentheses; these apply to all configs.

Many optional parameters enable additional Caliper functionality. For example, the profile.mpi option enables MPI function profiling, the io.bytes option reports I/O bytes written and read, and the mem.highwatermark option reports the memory high-watermark. In the example below, the mem.highwatermark option for runtime-report adds the “Allocated MB” column that shows the maximum amount of memory that was allocated in each region:

$ ./examples/apps/cxx-example -P runtime-report,mem.highwatermark
Path       Min time/rank Max time/rank Avg time/rank Time %   Allocated MB
main            0.000179      0.000179      0.000179 2.054637     0.000047
  mainloop      0.000082      0.000082      0.000082 0.941230     0.000016
    foo         0.000778      0.000778      0.000778 8.930211     0.000016
  init          0.000020      0.000020      0.000020 0.229568     0.000000

You can use the cali-query and mpi-caliquery programs to list available configs and their parameters (note that cali-query does not list MPI-dependent options and configs). For example, mpi-caliquery --help=configs lists all configs and their options. You can also query parameters for a specific config, e.g. mpi-caliquery --help=runtime-report.

Some available performance measurement configs include:


Print a time profile for annotated regions.


Print summary and time-series information for loops.


Print time spent in MPI functions.


Print time spent in functions using call-path sampling. See Sample profiling.


Record and print CUDA activities (kernel executions, memcopies, etc.) See GPU profiling.


Record CUDA activities and a write profile file (json or .cali) See GPU profiling.


Record and print OpenMP performance metrics (loops, barriers, etc.). Requires OMPT support. See OpenMP profiling.


Record a trace of region enter/exit events in .cali format. See Event tracing and timelines.


Record a region time profile for processing with hatchet or cali-query.


Record a sampling profile for processing with hatchet or cali-query. See Sample profiling.


Record a time profile for the Spot web visualization framework.

We discuss some of these configurations below. For a complete reference of the configuration string syntax and available configs and parameters, see Built-in profiling configurations.

You can also create entirely custom measurement configurations by selecting and configuring Caliper services manually. See Manual configuration to learn more.

Loop profiling

Loop profiling allows analysis of performance over time in iterative programs. To use loop profiling, annotate loops and loop iterations with Caliper’s loop annotation macros:

CALI_CXX_MARK_LOOP_BEGIN(mainloop_id, "mainloop");

for (int i = 0; i < N; ++i) {
    CALI_CXX_MARK_LOOP_ITERATION(mainloop_id, i);
    // ...


The CALI_CXX_MARK_LOOP_BEGIN macro gets a unique identifier (mainloop_id in the example) that is referenced in the subsequent iteration marker and loop end macros, as well as a user-defined name for the loop (here: “mainloop”).

Like other region annotations, loop and iteration annotations are meant for high-level regions, not small, frequently executed loops inside kernels. We recommend to only annotate top-level loops, such as the main timestepping loop in a simulation code. With the loop annotations in place, we can use the loop-report config to print loop performance information:

$ ./examples/apps/cxx-example -P loop-report 5000
Loop summary:

Loop     Iterations Time (s) Iter/s (min) Iter/s (max) Iter/s (avg)
mainloop       5000 7.012186   389.323701  2406.931322   713.178697

Iteration summary (mainloop):

Block Iterations Time (s) Iter/s
    0       1204 0.500222 2406.931322
 1204        536 0.500921 1070.029007
 1740        429 0.500715  856.774812
 2169        365 0.501464  727.868800
 2534        324 0.500800  646.964856
 2858        295 0.501248  588.531027
 3153        272 0.500612  543.334958
 3425        254 0.501714  506.264525
 3679        249 0.501720  496.292753
 3928        237 0.500152  473.855948
 4165        223 0.501182  444.948143
 4388        215 0.501665  428.572852
 4603        203 0.501471  404.809052
 4806        194 0.498300  389.323701

Here, we run the cxx-example program with 5000 loop iterations. The loop-report config prints an overall performance summary (“Loop summary”) and a time-series summary (“Iteration summary”) for each instrumented top-level loop. The iteration summary shows loop performance grouped by iteration blocks. By default, the report shows at most 20 iteration blocks. The block size adapts to cover the entire loop.

Caliper’s loop profiling typically does not measure every single iteration. By default, we take measurements at iteration boundaries after at least 0.5 seconds have passed since the previous measurement. This keeps the runtime overhead of loop profiling very low. The example program adds an increasing delay in each loop iteration. In the output above, we see this in the decreasing amount of iterations in each block and decreasing performance (“Iter/s”). Because of the time-based measurements, the time for each iteration block is the same.

We can configure the measurement mode and output. The iteration_interval option switches to an iteration-based instead of a time-based measurement interval. For example, we can take measurements every 500 loop iterations:

$ ./examples/apps/cxx-example -P loop-report,iteration_interval=500 5000
Iteration summary (mainloop):

Block Iterations Time (s) Iter/s
               0 0.000032    0.000000
    0        500 0.110812 4512.146699
  500        500 0.244453 2045.382957
 1000        500 0.378453 1321.168018
 1500        500 0.532856  938.339814
 2000        500 0.660435  757.076775
 2500        500 0.785368  636.644223
 3000        500 0.911957  548.271465
 3500        500 1.034089  483.517376
 4000        500 1.159672  431.156396
 4500        500 1.285956  388.815792

Now, the iterations per block remain at 500, whereas the time for each block increases. The iterations per second (“Iter/s”) column provides a useful performance metric independent of the measurement mode.

The report aggregates the data into a maximum number of iteration blocks (20 by default) to avoid visual clutter in programs with long-running loops. We can change this number with the timeseries.maxrows option. For example, we can choose a maximum of 3 blocks:

$ ./examples/apps/cxx-example -P loop-report,iteration_interval=500,timeseries.maxrows=3 5000
Iteration summary (mainloop):

Block Iterations Time (s) Iter/s
               0 0.000034    0.000000
    0       2000 1.294308 1545.227257
 1666       1500 2.359132  635.827075
 3332       1500 3.484032  430.535655

Setting timeseries.maxrows=0 disables the block limit and outputs all measured blocks. Thus, the configuration


shows performance data for every single loop iteration.

We can enable other performance metrics in the loop report, such as the memory high-water mark:

$ ./examples/apps/cxx-example -P loop-report,timeseries.maxrows=4,mem.highwatermark 5000
Loop summary:

Loop     Iterations Time (s) Iter/s (min) Iter/s (max) Iter/s (avg) Allocated MB
mainloop       5000 7.138860   371.436531  2408.400822   684.238039     0.000016

Iteration summary (mainloop):

Block Iterations Time (s) Iter/s      Allocated MB
    0       1745 1.001062 1743.148776     0.000016
 1250        788 1.000955  787.248178     0.000016
 2500       1382 2.502447  552.259448     0.000016
 3750       1085 2.634396  411.859113     0.000016

See Built-in profiling configurations or run mpi-caliquery --help=loop-report to learn about all loop-report options. Loop profiling is also available with other configs, notably the spot config producing output for the Spot performance visualization web framework.

Recording program metadata

Caliper can record and store program metadata, such as the system and program configuration, in its output files. This is useful for studies that compare data from multiple runs, such as scaling studies.

The Caliper annotation API provides the cali_set_global_(double|int|string|uint)_byname() family of functions to save global attributes in the form of key-value pairs:

cali_set_global_int_byname("iterations", iterations);
cali_set_global_string_byname("caliper.config", configstr.c_str());

Most machine-readable output formats, e.g. the hatchet JSON format written by the hatchet-region-profile config, include this data:

$ ./examples/apps/cxx-example -P hatchet-region-profile,output=stdout
"data": [
"caliper.config": "hatchet-region-profile,output=stdout",
"iterations": "4",
"cali.caliper.version": "2.5.0-dev",
"": "hatchet-region-profile"

Note how the “iterations” and “caliper.config” attributes are stored as top-level attributes in the JSON output. Caliper adds some built-in metadata attributes as well, such as the Caliper version (“cali.caliper.version”).

An even better way to record metadata is the Adiak library. Adiak makes metadata attributes accessible to multiple tools, and provides built-in functionality to record common information such as user name, executable name, command-line arguments, etc. The example below uses Adiak to record the “iterations” and “caliper.config” attributes as shown above, and also the user name, launch date, and MPI job size:


adiak::value("iterations", iterations);
adiak::value("caliper.config", configstr.c_str());

Most Caliper configs automatically import metadata attributes set through Adiak (Adiak support must be enabled in the Caliper build configuration). The spot config for the Spot web visualization framework requires that metadata attributes are recorded through Adiak.

Third-party tool support (NVidia NSight, Intel VTune)

Caliper provides bindings to export Caliper-annotated source code regions to third-party tools. Currently, Nvidia’s NVTX API for the NVProf/NSight profilers and Intel’s ITT API for Intel VTune Amplifier are supported.

To use the NVTX forwarding, activate the “nvtx” Caliper config when recording data with nvprof or ncu, either with the CALI_CONFIG environment variable, or the ConfigManager API. Be sure to enable NVTX support in NSight Compute.

To use the vtune bindings, run the target application in VTune with the vtune service enabled. To do so in the VTune GUI, do the following:

  • In the “Analysis Target” tab, go to the “User-defined environment variables” section, and add an entry setting “CALI_SERVICES_ENABLE” to “vtune”

  • In the “Analysis Type” tab, check the “Analyze user tasks, events, and counters” checkbox.

Caliper-annotated regions will then be visible as “tasks” in the VTune analysis views.

C++ example program

// Copyright (c) 2015-2022, Lawrence Livermore National Security, LLC.
// See top-level LICENSE file for details.

// A C++ Caliper instrumentation and ConfigManager example

//   Usage: $ cxx-example [-P <configuration-string>] <iterations>
// For example, "$ cxx-example -P runtime-report" will print a
// hierarchical runtime summary for all annotated regions.

#include <caliper/cali.h>
#include <caliper/cali-manager.h>

#include <time.h>

#include <cstring>
#include <iostream>
#include <string>

void print_help(const cali::ConfigManager& mgr)
    std::cerr << "Usage: cxx-example [-P caliper-config(arg=...,),...] [iterations]."
              << "\nAvailable configurations: ";

    auto configs = mgr.available_config_specs();

    // Print info on all available ConfigManager configurations.
    for (auto str : configs)
        std::cerr << "\n" << mgr.get_documentation_for_spec(str.c_str());

    std::cerr << std::endl;

double foo(int i)
    //   A function annotation. Opens region "function=foo" in Caliper,
    // and automatically closes it at the end of the function.

    struct timespec sleeptime { 0, std::max<time_t>(i * 500, 100000) };
    nanosleep(&sleeptime, nullptr);

    return 0.5*i;

int main(int argc, char* argv[])
    //   The ConfigManager manages built-in or custom Caliper measurement
    // configurations, and provides an API to control performance profiling.
    cali::ConfigManager mgr;

    //   Parse command-line arguments. Let users choose a Caliper performance
    // profiling configuration via the "-P" command-line argument.
    std::string configstr;
    int iterations = 4;

    for (int a = 1; a < argc; ++a) {
        if (strcmp(argv[a], "-h") == 0 || strcmp(argv[a], "--help") == 0) {
            return 0;
        } else if (strcmp(argv[a], "-P") == 0) {
            if (argc > a)
                configstr = argv[a];
            else {
                std::cerr << "Expected config string after \"-P\"";
                return 1;
        } else {
            try {
                iterations = std::stoi(argv[a]);
            } catch (std::invalid_argument) {
                std::cerr << "Invalid argument: \"" << argv[a]
                          << "\". Expected a number."
                          << std::endl;
                return 2;

    //   Enable the requested performance measurement channels and start
    // profiling.

    if (mgr.error())
        std::cerr << "Caliper config error: " << mgr.error_msg() << std::endl;


    //   Add some run metadata information to be stored in the
    // performance profiles.
    cali_set_global_int_byname("iterations", iterations);
    cali_set_global_string_byname("caliper.config", configstr.c_str());

    //   Mark begin of the current function. Must be manually closed.
    // Opens region "function=main" in Caliper.

    // Mark a code region. Opens region "annotation=init" in Caliper.
    double t = 0;

    // Mark a loop. Opens region "loop=mainloop" in Caliper.
    CALI_CXX_MARK_LOOP_BEGIN(loop_ann, "mainloop");

    for (int i = 0; i < iterations; ++i) {
        //   Mark loop iterations of an annotated loop.
        // Sets "iteration#main loop=<i> in Caliper.
        CALI_CXX_MARK_LOOP_ITERATION(loop_ann, i);

        //   A Caliper snapshot taken at this point will contain
        // { "function"="main", "loop"="mainloop", "iteration#main loop"=<i> }

        t += foo(i);

    // Mark the end of the "loop=mainloop" region.
    // Mark the end of the "function=main" region.

    //   Trigger output in all Caliper control channels.
    // This should be done after all measurement regions have been closed.