This FAQ is for Open MPI v4.x and earlier.
If you are looking for documentation for Open MPI v5.x and later, please visit docs.open-mpi.org.
Table of contents:
- What is VampirTrace?
- Where can I find the complete documentation of VampirTrace?
- How to instrument my MPI application with VampirTrace?
- Does VampirTrace cause overhead to my application?
- How can I change the underlying compiler of the
mpi*-vt wrappers?
- How can I pass VampirTrace related configure options through the
Open MPI configure?
- How to disable the integrated VampirTrace, completely?
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
VampirTrace is a program tracing package that can collect a
very fine grained event trace of your sequential or parallel
program. The traces can be visualized by the Vampir tool and a number
of other tools that read the Open Trace Format (OTF).
Tracing is interesting for performance analysis and optimization of
parallel and HPC (High Performance Computing) applications in general
and MPI programs in particular. In fact, that's where the letters
'mpi' in "Vampir" come from. Therefore, it is integrated into Open MPI
for convenience.
VampirTrace is included in Open MPI v1.3 and later.
VampirTrace consists of two main components: First, the
instrumentation part which slightly modifies the target program in
order to be notified about run-time events of interest. Simply replace
the compiler wrappers to activate it: mpicc to mpicc-vt, mpicxx
to mpicxx-vt and so on (note that the *-vt variants of the wrapper
compilers are unavailable before Open MPI v1.3). Second, the
run-time measurement part is responsible for data collection. This
can only be effective when the first part was performed — otherwise
there will be no effect on your program at all.
VampirTrace has been developed at ZIH, TU Dresden in collaboration with
the KOJAK project from JSC/FZ Juelich and is available as open source
software under the BSD license; see ompi/contrib/vt/vt/COPYING.
The software is also available as a stand-alone source code
package. The latest version can always be found at http://www.tu-dresden.de/zih/vampirtrace/.
| 2. Where can I find the complete documentation of VampirTrace? |
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
A complete documentation of VampirTrace comes with the Open
MPI software package as PDF and HTML. You
can find it in the Open MPI source tree at ompi/contrib/vt/vt/doc/ or
after installing Open MPI in
$(install-prefix)/share/vampirtrace/doc/.
| 3. How to instrument my MPI application with VampirTrace? |
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
All the necessary instrumentation of user functions as well as
MPI and OpenMP events is handled by special compiler wrappers (
mpicc-vt, mpicxx-vt, mpif77-vt, mpif90-vt ). Unlike the normal
wrappers ( mpicc and friends) these wrappers call VampirTrace's
compiler wrappers ( vtcc, vtcxx, vtf77, vtf90 ) instead of the
native compilers. The vt* wrappers use underlying platform compilers
to perform the necessary instrumentation of the program and link the
suitable VampirTrace library.
Original:
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| shell$ mpicc -c hello.c -o hello |
With instrumentation:
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| shell$ mpicc-vt -c hello.c -o hello |
For your application, simply change the compiler definitions in your
Makefile(s):
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| # original definitions in Makefile
## CC=mpicc
## CXX=mpicxx
## F90=mpif90
# replace with
CC=mpicc-vt
CXX=mpicxx-vt
F90=mpif90-vt |
| 4. Does VampirTrace cause overhead to my application? |
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
By using the default MPI compiler wrappers ( mpicc, etc.) your
application will be run without any changes at all. The VampirTrace
compiler wrappers ( mpicc-vt etc.) link the VampirTrace library which intercepts
MPI calls and some user level function/subroutine calls. This causes a certain
amount of run-time overhead to applications. Usually, the overhead is reasonably
small (0.x% - 5%) and VampirTrace by default enables precautions to avoid
excessive overhead. However, it can be configured to produce very substantial
overhead using non-default settings.
5. How can I change the underlying compiler of the mpi*-vt wrappers? |
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
Unlike the standard MPI compiler wrappers ( mpicc etc.) the
environment variables OMPI_CC, OMPI_CXX, OMPI_F77, OMPI_F90 do not
affect the VampirTrace compiler wrappers. Please, use the environment
variables VT_CC, VT_CXX, VT_F77, VT_F90 instead. In addition, you
can set the compiler with the wrapper's option -vt:[cc|cxx|f77|f90]
The following two are equivalent, setting the underlying compiler to
gcc:
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| shell$ VT_CC=gcc mpicc-vt -c hello.c -o hello
shell$ mpicc-vt -vt:cc gcc -c hello.c -o hello |
Futhermore, you can modify the default settings in
/share/openmpi/mpi*-wrapper-data.txt.
| 6. How can I pass VampirTrace related configure options through the
Open MPI configure? |
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
To give options to the VampirTrace configure script you can add this
to the configure option: --with-contrib-vt-flags.
The following example passes the options --with-papi-lib-dir and --with-papi-lib
to the VampirTrace configure script to specify the location and name of the PAPI
library:
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| shell$ ./configure --with-contrib-vt-flags='--with-papi-lib-dir=/usr/lib64 --with-papi-lib=-lpapi64' ... |
| 7. How to disable the integrated VampirTrace, completely? |
NOTE: VampirTrace was only included in Open
MPI from v1.3.x through v1.10.x. It was removed in the v2.0.0 release
of Open MPI. This FAQ question pertains to the versions of Open MPI
that contained VampirTrace.
By default, the VampirTrace part of Open MPI will be built and
installed. If you would like to disable building and installing of
VampirTrace, add the value vt to the configure option
--enable-contrib-no-build.
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| shell$ ./configure --enable-contrib-no-build=vt ... |
|
