VampirTrace

VampirTrace consists of a tool set and a runtime library for instrumentation and tracing of software applications. It is particularly tailored to parallel and distributed High Performance Computing (HPC) applications.

Availability

VampirTrace is currently available on FutureGrid machines under module 'vampirtrace'. VampirTrace is also available in OpenMPI versions 1.5.x or higher. For example on Bravo, it is available as openmpi/1.5.4-gnu or openmpi/1.5.4-intel.

Overview

The instrumentation part of VampirTrace modifies a given application in order to inject additional measurement calls during runtime. The tracing part provides the actual measurement functionality used by the instrumentation calls. By this means, a variety of detailed performance properties can be collected and recorded during runtime. This includes function enter and leave events, MPI communication, OpenMP events, and performance counters.

After a successful tracing run, VampirTrace writes all collected data to a trace file in the Open Trace Format (OTF). As a result, the information is available for post-mortem analysis and visualization by various tools. Most notably, VampirTrace provides the input data for the Vampir analysis and visualization tool.

Trace files can quickly become very large, especially with automatic instrumentation. Tracing applications for only a few seconds can result in trace files of several hundred megabytes. To protect users from creating trace files of several gigabytes, the default behavior of VampirTrace limits the internal buffer to 32MB per process (2GB on FutureGrid systems). Thus, even for larger scale runs the total trace file size will be moderate.

The following list shows a summary of all instrumentation and tracing features that VampirTrace offers. Note that not all features are supported on all platforms.

Tracing of User Functions

• Record function enter and leave events
• Record name and source code location (file name, line)
• Manual instrumentation using VampirTrace API

MPI Tracing

• Record MPI functions
• Record MPI communication: participating processes, transferred bytes, tag, communicator

OpenMP Tracing

• OpenMP directives, synchronization, thread idle time
• Also hybrid (MPI and OpenMP) applications are supported

Pthread Tracing

• Trace POSIX thread API calls
• Also hybrid (MPI and POSIX threads) applications are supported

Java Tracing

• Record method calls
• Using JVMTI as interface between VampirTrace and Java Applications

3rd-Party Library tracing

• Trace calls to arbitrary third party libraries
• Generate wrapper for library functions based on library’s header file(s)
• No recompilation of application or library is required

MPI Correctness Checking

• Record MPI usage errors
• Using UniMCI as interface between VampirTrace and a MPI correctness checking tool (e.g., Marmot)

User API

• Manual instrumentation of source code regions
• Measurement controls
• User-defined counters
• User-defined marker

Performance Counters

• Hardware performance counters using PAPI, CPC, or NEC SX performance counter
• Resource usage counters using getrusage

Memory Tracing

• Trace GLIBC memory allocation and free functions
• Record size of currently allocated memory as counter

I/O Tracing

• Trace LIBC I/O calls
• Record I/O events: file name, transferred bytes

CPU ID Tracing

• Trace core ID of a CPU on which the calling thread is running
• Record core ID as counter

Fork/System/Exec Tracing

• Trace applications calling LIBC’s fork, system, or one of the exec functions
• Add forked processes to the trace

Filtering & Grouping

• Runtime and post-mortem filter (i.e., exclude functions from being recorded in the trace)
• Runtime grouping (i.e., assign functions to groups for improved analysis)

OTF Output

• Writes compressed OTF files
• Output as trace file, statistical summary (profile), or both

Instrumentation

To perform measurements with VampirTrace, the user's application program needs to be instrumented; that is, at specific points of interest (called "events"), VampirTrace measurement calls have to be activated. Common events are, among others, entering and leaving of functions as well as sending and receiving of MPI messages. VampirTrace handles this automatically by default. In order to enable the instrumentation of function calls, the user needs only to replace the compiler and linker commands with VampirTrace’s wrappers (see below). VampirTrace supports different ways of instrumentation as described in the sections below.

Compiler Wrappers

All the necessary instrumentation of user functions, MPI, and OpenMP events is handled by VampirTrace’s compiler wrappers (vtcc, vtcxx, vtf77, and vtf90). In the script used to build the application (e.g., a makefile), all compile and link commands should be replaced by the VampirTrace compiler wrapper. The wrappers perform the necessary instrumentation of the program and link the suitable VampirTrace library. The following list shows some examples specific to the parallelization type of the program:

• Serial programs

Compiling serial codes is the default behavior of the wrappers. Simply replace the compiler by VampirTrace’s wrapper:

This will instrument user functions (if supported by the compiler) and link the VampirTrace library.

• MPI parallel programs

MPI instrumentation is always handled by means of the PMPI interface, which is part of the MPI standard. This requires the compiler wrapper to link with an MPI-aware version of the VampirTrace library. If your MPI implementation uses special MPI compilers (e.g. mpicc, mpxlf90), you will need to tell VampirTrace’s wrapper to use this compiler instead of the serial one:

MPI implementations without their own compilers require the user to link the MPI library manually. In this case, simply replace the compiler by VampirTrace’s compiler wrapper:

If you want to instrument MPI events only (this creates smaller trace files and less overhead), use the option -vt:inst manual to disable automatic instrumentation of user functions.

• Threaded parallel programs

When VampirTrace detects OpenMP or Pthread flags on the command line, special instrumentation calls are invoked. For OpenMP events, OPARI is invoked for automatic source code instrumentation.

For more information about OPARI, read the documentation available in VampirTrace’s installation directory at: share/vampirtrace/doc/opari/Readme.html

• Hybrid MPI/Threaded parallel programs

With a combination of the above mentioned approaches, hybrid applications can be instrumented:

The VampirTrace compiler wrappers automatically try to detect which parallelization method is used by means of the compiler flags (e.g., -lmpi, -openmp or -pthread) and the compiler command (e.g. mpif90). If the compiler wrapper failed to detect this correctly, the instrumentation could be incomplete and an unsuitable VampirTrace library would be linked to the binary. In this case, you should tell the compiler wrapper which parallelization method your program uses by using the switches -vt:mpi, -vt:mt, and -vt:hyb for MPI, multithreaded, and hybrid programs, respectively. Note that these switches do not change the underlying compiler or compiler flags. Use the option -vt:verbose to see the command line that the compiler wrapper executes.

The default settings of the compiler wrappers can be modified in the files share/vampirtrace/vtcc-wrapper-data.txt (and similar for the other languages) in the installation directory of VampirTrace. The settings include compilers, compiler flags, libraries, and instrumentation types. You could, for instance, modify the default C compiler from gcc to mpicc by changing the line compiler=gcc to compiler=mpicc. This may be convenient if you instrument MPI parallel programs only.

Instrumentation Types

The wrapper option -vt:inst <insttype> specifies the instrumentation type to be used. The following values for <insttype> are possible:

• compinst

Fully-automatic instrumentation by the compiler

• manual

Manual instrumentation by using VampirTrace’s API (needs source-code modifications)

Automatic Instrumentation

Automatic instrumentation is the most convenient method to instrument your program. If available, simply use the compiler wrappers without any parameters, e.g.:

Notes for Using the GNU or Intel Compiler

For these compilers, the command nm is required to get symbol information of the running application executable. To get the application executable for nm during runtime, VampirTrace uses the /proc file system. As /proc is not present on all operating systems, automatic symbol information might not be available. In this case, it is necessary to set the environment variable VT APPPATH to the pathname of the application executable to get symbols resolved via nm.

Should any problems emerge to get symbol information automatically, then the environment variable VT GNU NMFILE can be set to a symbol list file, which is created with the command nm, like:

To get the source code line for the application functions use nm -l (on Linux systems). VampirTrace will include this information in the trace. Note that the output format of nm must be written in BSD-style. See the manual page of nm for help in dealing with the output format setting.

Notes on Instrumentation of Inline Functions

Compilers behave differently when they automatically instrument inlined functions. The GNU and Intel (10.0++) compilers instrument all functions by default when they are used with VampirTrace. They therefore switch off inlining completely, disregarding the optimization level chosen. One can prevent these particular functions from being instrumented by appending the following attribute to function declarations, hence making them able to be inlined (this works only for C/C++):

The PGI and IBM compilers prefer inlining over instrumentation when compiling with enabled inlining. Thus, one needs to disable inlining to enable the instrumentation of inline functions and vice versa.

The bottom line is that a function cannot be inlined and instrumented at the same time. Note that you can also use the option -vt:inst manual with non-instrumented sources. Binaries created in this manner only contain MPI and OpenMP instrumentation, which might be desirable in some cases. For more on how to inline functions, read your compiler’s manual.

Manual Instrumentation

Using the VampirTrace API

The VT USER START, VT USER END calls can be used to instrument any user-defined sequence of statements.

Fortran

C

If a block has several exit points (as is often the case for functions), all exit points have to be instrumented with VT USER END, too.

For C++ it is simpler, as is demonstrated in the following example. Only entry points into a scope need to be marked. The exit points are detected automatically when C++ deletes scope-local variables.

C++

The instrumented sources have to be compiled with -DVTRACE for all three languages; otherwise the VT * calls are ignored. Note that Fortran source files instrumented this way have to be preprocessed, too.

In addition, you can combine this particular instrumentation type with all other types. In such a way, all user functions can be instrumented by a compiler while special source code regions (e.g., loops) can be instrumented by VT’s API.

Use VT’s compiler wrapper (described above) for compiling and linking the instrumented source code, such as:

• combined with automatic compiler instrumentation:

• without compiler instrumentation:

Note that you can also use the option -vt:inst manual with non-instrumented sources. Binaries created in this manner only contain MPI and OpenMP instrumentation, which might be desirable in some cases.

Measurement Controls

Switching Tracing On/Off: In addition to instrumenting arbitrary blocks of code, one can use the VT_ON/ VT_OFF instrumentation calls to start and stop the recording of events. These constructs can be used to stop recording of events for a part of the application and later resume recording. For example, one could not collect trace events during the initialization phase of an application and turn on tracing for the computation part.

Furthermore, the "on/off" functionality can be used to control the tracing behavior of VampirTrace, and allows you to trace only parts of interests. Essentially, then, the amount of trace data can be reduced.

To check whether if tracing is enabled or not, use the call VT_IS_ON.

Please note that stopping and starting the recording of events has to be performed at the same call stack level. If this is not the case, an error message will be printed during runtime, and VampirTrace will abort execution.

Intermediate Buffer Flush: In addition to an automated buffer flush when the buffer is filled, it is possible to flush the buffer at any point of the application. This way you can guarantee that after a manual buffer flush there will be a sequence of the program with no automatic buffer flush interrupting. To flush the buffer, you can use the call VT_BUFFER_FLUSH.

Intermediate Time Synchronisation: VampirTrace provides several mechanisms for timer synchronization. In addition, it is also possible to initiate a timer synchronization at any point of the application by calling VT_TIMESYNC. Please note that the user has to ensure that all processes are actual at a synchronized point in the program (e.g., at a barrier). To use this call, make sure that the enhanced timer synchronization is activated (set the environment variable VT_ETIMESYNC).

Intermediate Counter Update: VampirTrace provides the functionality to collect the values of arbitrary hardware counters. Chosen counter values are automatically recorded whenever an event occurs. Sometimes (e.g., within a long-lasting function) it is desirable to get the counter values at an arbitrary point within the program. To record the counter values at any given point, you can call VT_UPDATE_COUNTER.

Note: For all three languages the instrumented sources have to be compiled with -DVTRACE. Otherwise the VT * calls are ignored. In addition, if the sources contain further VampirTrace API calls and only the calls for measurement controls will be disabled, then the sources must also be compiled with -DVTRACE_NO_CONTROL.

Tracing Calls to 3rd-Party Libraries

VampirTrace is also capable of tracing calls to third-party libraries which come with at least one C header file, even without the library’s source code. If VampirTrace was built with support for library tracing, the tool vtlibwrapgen can be used to generate a wrapper library to intercept each call to the actual library functions. This wrapper library can be linked to the application, or used in combination with the LD PRELOAD mechanism provided by Linux. The generation of a wrapper library is done using the vtlibwrapgen command and consists of two steps. The first step generates a C source file, providing the wrapped functions of the library header file:

This generates the source file SDLwrap.c that contains wrapper-functions for all library functions found in the header-files located in /usr/include/SDL/ , and instructs VampirTrace to assign these functions to the new group SDL. The generated wrapper source file can be edited in order to add manual instrumentation or alter attributes of the library wrapper. A detailed description can be found in the generated source file or in the header file vt libwrap.h , which can be found in the include directory of VampirTrace. To adapt the library instrumentation it is possible to pass a filter file to the generation process. The rules are like these for normal VampirTrace instrumentation, where only 0 (exclude functions) and -1 (generally include functions) are allowed.

The second step is to compile the generated source file:

This builds the shared library libSDLwrap.so , which can be linked to the application or preloaded by using the environment variable LD PRELOAD:

Runtime Measurement

Running a VampirTrace instrumented application should normally result in an OTF trace file in the current working directory where the application was executed. If a problem occurs, set the environment variable VT_VERBOSE to 2 before executing the instrumented application in order to see control messages of the VampirTrace runtime system which might help tracking down the problem.

The internal buffer of VampirTrace is limited to 32 MB per process. Use the environment variables VT_BUFFER_SIZE and VT_MAX_FLUSHES to increase this limit.

Trace File Name and Location

The default name of the trace file depends on the operating system where the application is run. On Linux, MacOS and Sun Solaris, the trace file will be named like the application, e.g., hello.otf for the executable hello. For other systems, the default name is a.otf. Optionally, the trace file name can be defined manually by setting the environment variable VT_FILE_PREFIX to the desired name. The suffix .otf will be added automatically.

To prevent overwriting of trace files by repetitive program runs, one can enable unique trace file naming by setting VT_FILE_UNIQUE to yes. In this case, VampirTrace adds a unique number to the file names as soon as a second trace file with the same name is created. A *.lock file is used to count up the number of trace files in a directory. Be aware that VampirTrace potentially overwrites an existing trace file if you delete this lock file. The default value of VT_FILE_UNIQUE is no. You can also set this variable to a number greater than zero, which will be added to the trace file name. This way you can manually control the unique file naming.

The default location of the final trace file is the working directory at application start time. If the trace file will be stored in another place, use VT_PFORM_GDIR to change the location of the trace file.

Environment Variables

Environment variables can be used to control nearly every aspect of the measurement of a VampirTrace instrumented executable. (ToDo: link to CheatSheet and Doku-PDF)

When you use these environment variables, make sure that they have the same value for all processes of your application on all nodes of your cluster. Some cluster environments do not automatically transfer your environment when executing parts of your job on remote nodes of the cluster, and you may need to explicitly set and export them in batch job submission scripts.

Influencing Trace Buffer Size

The default values of the environment variables VT_BUFFER_SIZE and VT_MAX_FLUSHES limit the internal buffer of VampirTrace to 32 MB per process, and the number of times that the buffer is flushed to 1, respectively. Events that are to be recorded after the limit has been reached are no longer written into the trace file. The environment variables apply to every process of a parallel application, meaning that applications with n processes will typically create trace files n times the size of a serial application.

To remove the limit and get a complete trace of an application, set VT_MAX_FLUSHES to 0. This causes VampirTrace to always write the buffer to disk when it is full. To change the size of the buffer, use the environment variable VT_BUFFER_SIZE. The optimal value for this variable depends on the application which is to be traced. Setting a small value will increase the memory available to the application, but will trigger frequent buffer flushes by VampirTrace. These buffer flushes can significantly change the behavior of the application. On the other hand, setting a large value, like 2G, will minimize buffer flushes by VampirTrace, but decrease the memory available to the application. If not enough memory is available to hold the VampirTrace buffer and the application data, parts of the application may be swapped to disk, leading to a significant change in the behavior of the application.

Note that you can decrease the size of trace files significantly by using the runtime function filtering.

Profiling an Application

Profiling an application collects aggregated information about certain events during a program run, whereas tracing records information about individual events. Profiling can therefore be used to get a summary of the program activity and to detect events that are called very often. The profiling information can also be used to generate filter rules to reduce the trace file size.

To profile an application, set the variable VT_MODE to STAT. Setting VT_MODE to STAT:TRACE tells VampirTrace to perform tracing and profiling at the same time. By setting the variable VT STAT PROPS, the user can influence whether functions, messages, and/or collective operations shall be profiled.

Unification of Local Traces

After a run of an instrumented application, the traces of the single processes need to be unified in terms of timestamps and event IDs. In most cases, this happens automatically. If the environment variable VT_UNIFY is set to no, and in the case of certain other circumstances, it will be necessary to perform unification of local traces manually. To do this, use the following command:

If VampirTrace was built with support for OpenMP and/or MPI, it is possible to speedup the unification of local traces significantly. To distribute the unificationon multible processes, the MPI parallel version vtunify-mpi can be used as follows:

Furthermore, both tools vtunify and vtunify-mpi are capable of opening additional OpenMP threads for unification. The number of threads can be specified by the OMP_NUM_THREADS environment variable.

Synchronized Buffer Flush

When tracing an application, VampirTrace temporarily stores the recorded events in a trace buffer. Typically, if a buffer of a process or thread has reached its maximum fill level, the buffer has to be flushed and other processes or threads may have to wait for this process or thread. This will result in an asynchronous runtime behavior.

To avoid this problem, VampirTrace provides a buffer flush in a synchronized manner. This means that if one buffer has reached its minimum buffer fill level VT_SYNC_FLUSH_LEVEL, all buffers will be flushed. This buffer flush is only available at appropriate points in the program flow. Currently, VampirTrace makes use of all MPI collective functions associated with MPI_COMM_WORLD. Use the environment variable VT_SYNC_FLUSH to enable synchronized buffer flush.

Enhanced Timer Synchronization

Especially on cluster environments, where each process has its own local timer, tracing relies on precisely synchronized timers. Therefore, VampirTrace provides several mechanisms for timer synchronization. The default synchronization scheme is a linear synchronization at the very beginning and very end of a trace run with a master-slave communication pattern.

However, this way of synchronization can become too imprecise for long trace runs. Therefore, we recommend the usage of the enhanced timer synchronization scheme of VampirTrace. This scheme inserts additional synchronization phases at appropriate points in the program flow. Currently, VampirTrace makes use of all MPI collective functions associated with MPI_COMM_WORLD.

To enable this synchronization scheme, a LAPACK library with C wrapper support has to be provided for VampirTrace, and the environment variable VT_ETIMESYNC has to be set before the tracing. The length of the interval between two successive synchronization phases can be adjusted with VT_ETIMESYNC_INTV. The following LAPACK libraries provide a C-LAPACK API that can be used by VampirTrace for the enhanced timer synchronization:

• CLAPACK
• AMD ACML
• IBM ESSL
• Intel MKL
• SUN Performance Library

Note: Systems equipped with a global timer do not need timer synchronization.

Note: It is recommended to combine enhanced timer synchronization and synchronized buffer flush.

Note: Be aware that the asynchronous behavior of the application will be disturbed since VampirTrace makes use of asynchronous MPI collective functions for timer synchronization and synchronized buffer flush. Only make use of these approaches if your application does not rely on an asynchronous behavior! Otherwise, keep this fact in mind during the process of performance analysis.

Recording Additional Events and Counters

Hardware Performance Counters

If VampirTrace has been built with hardware counter support, it is capable of recording hardware counter information as part of the event records. To request the measurement of certain counters, the user is required to set the environment variable VT_METRICS. The variable should contain a colon-separated list of counter names or a predefined platform-specific group.

The user can leave the environment variable unset to indicate that no counters are requested. If any of the requested counters are not recognized or the full list of counters cannot be recorded due to hardware resource limits, program execution will be aborted with an error message.

PAPI Hardware Performance Counters

If the PAPI library is used to access hardware performance counters, metric names can be any PAPI preset names or PAPI native counter names. For example, set

to record the number of floating point instructions and level 2 cache misses.

Resource Usage Counters

The Unix system call getrusage provides information about consumed resources and operating system events of processes such as user/system time, received signals, and context switches.

If VampirTrace has been built with resource usage support, it is able to record this information as performance counters to the trace. You can enable tracing of specific resource counters by setting the environment variable VT_RUSAGE to a colon-separated list of counter names. For example, set

to record the system time consumed by each process and the number of page faults. Alternatively, one can set this variable to the value all to enable recording of all 16 resource usage counters. Note that not all counters are supported by all Unix operating systems. Linux 2.6 kernels, for example, support only resource information for six of them.

The resource usage counters are not recorded at every event. They are only read if 100 ms have passed since the last sampling. The interval can be changed by setting VT_RUSAGE_INTV to the number of desired milliseconds. Setting VT_RUSAGE_INTV to zero leads to sampling resource usage counters at every event, which may introduce a large runtime overhead. Note that in most cases the operating system does not update the resource usage information at the same high frequency as the hardware performance counters. Setting VT_RUSAGE_INTV to a value less than 10 ms does not usually improve the granularity.

Be aware that, when using the resource usage counters for multi-threaded programs, the information displayed is valid for the whole process and not for each single thread.

Memory Allocation Counter

The GNU LIBC implementation provides a special hook mechanism that allows intercepting all calls to memory allocation and free functions (e.g. malloc, realloc, free). This is independent from compilation or source code access, but relies on the underlying system library.

If VampirTrace has been built with memory-tracing support, VampirTrace is capable of recording memory allocation information as part of the event records. To request the measurement of the application’s allocated memory, the user must set the environment variable VT_MEMTRACE to yes.

Note: This approach to get memory allocation information requires changing internal function pointers in a non-thread-safe way, so VampirTrace currently does not support memory tracing for threadable programs, e.g., programs parallelized with OpenMP or Pthreads!

Pthread API Calls

When tracing applications with Pthreads, only user events and functions are recorded which are automatically or manually instrumented. Pthread API functions will not be traced by default. To enable tracing of all C-Pthread API functions, include the header vt user.h and compile the instrumented sources with -DVTRACE PTHREAD.

C/C++

I/O Calls

Calls to functions which reside in external libraries can be intercepted by implementing identical functions and linking them before the external library. Such "wrapper functions" can record the parameters and return values of the library functions.

If VampirTrace has been built with I/O tracing support, it uses this technique for recording calls to I/O functions of the standard C library, which are executed by the application. The following functions are intercepted by VampirTrace:

The gathered information will be saved as I/O event records in the trace file. This feature has to be activated for each tracing run by setting the environment variable VT_IOTRACE to yes.

This works for both dynamically and statically linked executables. Note that when linking statically, a warning like the following may be issued: Using "dlopen" in statically linked applications requires at runtime the shared libraries from the glibc version used for linking. This is ok as long as the mentioned libraries are available for running the application.

If you’d like to experiment with some other I/O library, set the environment variable VT_IOLIB_PATHNAME to the alternative one. Beware that this library must provide all I/O functions mentioned above; otherwise VampirTrace will abort.

fork/system/exec Calls

If VampirTrace has been built with LIBC trace support, it is capable of tracing programs which call functions from the LIBC exec family (execl, execlp, execle, execv, execvp, execve), system, and fork. VampirTrace records the call of the LIBC function to the trace. This feature works for sequential (i.e., no MPI or threaded parallelization) programs only. It works for both dynamically and statically linked executables. Note that when linking statically, a warning like the following may be issued: Using "dlopen" in statically linked applications requires at runtime the shared libraries from the glibc version used for linking. This is ok as long as the mentioned libraries are available for running the application.

When VampirTrace detects a call of an exec function, the current trace file is closed before executing the new program. If the executed program is also instrumented with VampirTrace, it will create a different trace file. Note that VampirTrace aborts if the exec function returns unsuccessfully. Calling fork in an instrumented program creates an additional process in the same trace file.

MPI Correctness Checking Using UniMCI

VampirTrace supports the recording of MPI correctness events, e.g., usage of invalid MPI requests. This is implemented by using the Universal MPI Correctness Interface (UniMCI), which provides an interface between tools like VampirTrace and existing runtime MPI correctness checking tools. Correctness events are stored as markers in the trace file and are visualized by Vampir. If VampirTrace is built with UniMCI support, the user only has to enable MPI correctness checking. This is done by merely setting the environment variable VT_MPICHECK to yes. Further, if your application crashes due to an MPI error you should set VT_MPICHECK_ERREXIT to yes. This environmental variable forces VampirTrace to write its trace to disk and exit afterwards. As a result, the trace with the detected error is stored before the application might crash.

To install VampirTrace with correctness checking support, it is necessary to have UniMCI installed on your system. UniMCI in turn requires you to have a supported MPI correctness checking tool installed (currently only the tool Marmot is known to have UniMCI support). So, all in all, you should use the following order to install with correctness checking support:

1. Marmot

http://www.hlrs.de/organization/av/amt/research/marmot

1. UniMCI

http://www.tu-dresden.de/zih/unimci

1. VampirTrace

http://www.tu-dresden.de/zih/vampirtrace

Information on how to install Marmot and UniMCI is given in their respective manuals. VampirTrace will automatically detect an UniMCI installation if the unimci-config tool is in path.

User-defined Counters

In addition to the manual instrumentation, the VampirTrace API provides instrumentation calls which allow recording of program variable values (e.g., iteration counts, calculation results, ...) or any other numerical quantity. A user-defined counter is identified by its name, the counter group it belongs to, the type of its value (integer or floating-point) and the unit that the value is quoted (e.g. "GFlop/sec"). The VT_COUNT_GROUP_DEF and VT_COUNT_DEF instrumentation calls can be used to define counter groups and counters:

Fortran

C/C++

The definition of a counter group is optional. If no special counter group is desired, the default group "User" can be used. In this case, set the parameter gid of VT_COUNT_DEF() to VT_COUNT_DEFGROUP. The third parameter type of VT_COUNT_DEF specifies the data type of the counter value. To record a value for any of the defined counters, the corresponding instrumentation call VT_COUNT * VAL must be invoked.

The following example records the loop index i:

Fortran

C/C++

For all three languages, the instrumented sources have to be compiled with -DVTRACE. Otherwise, the VT * calls are ignored. Optionally, if the sources contain further VampirTrace API calls and only the calls for user-defined counters will be disabled, then the sources have to be compiled with -DVTRACE_NO_COUNT in addition to -DVTRACE .

User-Defined Markers

In addition to the manual instrumentation, the VampirTrace API provides instrumentation calls which allow recording of special user information, which can be used to better identify parts of interest. A user-defined marker is identified by its name and type.

Fortran

C/C++

Types for Fortran/C/C++

For all three languages, the instrumented sources have to be compiled with -DVTRACE. Otherwise, the VT * calls are ignored. Optionally, if the sources contain further VampirTrace API calls and only the calls for user-defined markers will be disabled, then the sources have to be compiled with -DVTRACE_NO_MARKER in addition to -DVTRACE .

Filtering and Grouping

By default, all calls of instrumented functions will be traced; consequently, the resulting trace files can easily become very large. In order to decrease the size of a trace, VampirTrace allows the specification of filter directives before running an instrumented application. The user can decide on how often an instrumented function/region should be recorded to a trace file. To use a filter, the environment variable VT_FILTER_SPEC needs to be defined. It should contain the path and name of a file with filter directives. Following is an example of a file containing filter directives:

These region filter directives allow the functions add, sub, mul and div to be recorded at most 1000 times. The remaining functions * will be recorded at most 3,000,000 times.

Besides creating filter files manually, you can also use the vtfilter tool to generate them automatically. This tool reads a provided trace and decides whether a function should be filtered or not, based on the evaluation of certain parameters.

Rank Specific Filtering

An experimental extension allows rank specific filtering. Use @ clauses to restrict all following filters to the given ranks. The rank selection must be given as a list of <from> - <to> pairs or single values.

The example defines two limits for the ranks 4 - 10, 20 - 29, and 34.

Attention: The rank specific rules are activated later than usual at MPI Init, because the ranks are not available earlier. The special MPI routines MPI Init, MPI Init thread, and MPI Initialized cannot be filtered in this way.

Function Grouping

VampirTrace allows assigning functions/regions to a group. Groups can, for instance, be highlighted by different colors in Vampir displays. The following standard groups are created by VampirTrace:

Additionally, you can create your own groups, if, for example, you wish to better distinguish different phases of an application. To use function/region grouping, set the environment variable VT_GROUPS_SPEC to the path of a file which contains the group assignments. Below is an example of how to use group assignments:

These group assignments associate the functions add, sub, mul and div with group "CALC", and all functions with the prefix app are associated with group "USER".