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Portable test run of ESPResSo on EuroHPC systems via EESSI

ESPResSo logo

Since 14 June 2024, ESPResSo v4.2.2 is available in the EESSI production repository, optimized for the 8 CPU targets that are fully supported by version 2023.06 of EESSI. This allows running ESPResSo effortlessly on the EuroHPC systems where EESSI is already available, like Vega and Karolina.

On 27 June 2024, an additional installation of ESPResSo v4.2.2 that is optimized for Arm A64FX processors was added, which enables also running ESPResSo efficiently on Deucalion, even though EESSI is not available yet system-wide on Deucalion (see below for more details).

With the portable test for ESPResSo that is available in the EESSI test suite we can easily evaluate the scalability of ESPResSo across EuroHPC systems, even if those systems have different system architectures.

Simulating Lennard-Jones fluids using ESPResSo

Lennard-Jones fluids model interacting soft spheres with a potential that is weakly attractive at medium range and strongly repulsive at short range. Originally designed to model noble gases, this simple setup now underpins most particle-based simulations, such as ionic liquids, polymers, proteins and colloids, where strongly repulsive pairwise potentials are desirable to prevent particles from overlapping with one another. In addition, solvated systems with atomistic resolution typically have a large excess of solvent atoms compared to solute atoms, thus Lennard-Jones interactions tend to account for a large portion of the simulation time. Compared to other potentials, the Lennard-Jones interaction is inexpensive to calculate, and its limited range allows us to partition the simulation domain into arbitrarily small regions that can be distributed among many processors.

Portable test to evaluate performance of ESPResSo

To evaluate the performance of ESPResSo, we have implemented a portable test for ESPResSo in the EESSI test suite; the results shown here were collected using version 0.3.2.

After installing and configuring the EESSI test suite on Vega, Karolina, and Deucalion, running the Lennard-Jones (LJ) test case with ESPResSo 4.2.2 available in EESSI can be done with:

reframe --name "ESPRESSO_LJ.*%module_name=ESPResSo/4.2.2"

This will automatically run the LJ test case with ESPResSo across all known scales in the EESSI test suite, which range from single core up to 8 full nodes.

Performance + scalability results on Vega, Karolina, Deucalion

The performance results of the tests are collected by ReFrame in a detailed JSON report.

The parallel performance of ESPResSo, expressed in particles integrated per second, scales linearly with the number of cores. On Vega using 8 nodes (1024 MPI ranks, one per physical core), ESPResSo 4.2.2 can integrate the equations of motion of roughly 615 million particles every second. On Deucalion using 8 nodes (384 cores), we observe a performance of roughly 62 million particles integrated per second.

Performance of ESPResSo 4.2.2 on Vega, Karolina, Deucalion

Plotting the parallel efficiency of ESPResSo 4.2.2 (weak scaling, 2000 particles per MPI rank) on the three EuroHPC systems we used shows that it decreases approximately linearly with the logarithm of the number of cores.

Parallel efficiency of ESPResSo 4.2.2 on Vega, Karolina, Deucalion

Running ESPResSo on Deucalion via EESSI + cvmfsexec

While EESSI is already available system-wide on both Vega and Karolina for some time (see here and here for more information, respectively), it was not available yet on Deucalion when these performance experiments were run.

Nevertheless, we were able to leverage the optimized installation of ESPResSo for A64FX that is available in EESSI since 27 June 2024, by leveraging the cvmfsexec tool, and by creatively implementing two simple shell wrapper scripts.

cvmfsexec wrapper script

The first wrapper script can be used to run a command in a subshell in which the EESSI CernVM-FS repository ( is mounted via cvmfsexec. This script can be used by regular users on Deucalion, it does not require any special privileges beyond the Linux kernel features that cvmfsexec leverages, like user namespaces.

Contents of ~/bin/

if [ -d /cvmfs/ ]; then
    # run command directly, EESSI CernVM-FS repository is already mounted
    # run command via in subshell where EESSI CernVM-FS repository is mounted,
    # via cvmfsexec which is set up in a unique temporary directory
    mkdir -p /tmp/$USER
    tmpdir=$(mktemp -p /tmp/$USER -d)
    cd $tmpdir
    git clone > $tmpdir/git_clone.out 2>&1
    cd cvmfsexec
    ./makedist default > $tmpdir/cvmfsexec_makedist.out 2>&1
    cd $orig_workdir
    $tmpdir/cvmfsexec/cvmfsexec -- "$@"
    # cleanup
    rm -rf $tmpdir

Do make sure that this script is executable:

chmod u+x ~/bin/

A simple way to test this script is to use it to inspect the contents of the EESSI repository:

~/bin/ ls /cvmfs/

or to start an interactive shell in which the EESSI repository is mounted:

~/bin/ /bin/bash -l

The job scripts that were submitted by ReFrame on Deucalion leverage to set up the environment and get access to the ESPResSo v4.2.2 installation that is available in EESSI (see below).

orted wrapper script

In order to get multi-node runs of ESPResSo working without having EESSI available system-wide, we also had to create a small wrapper script for the orted command that is used by Open MPI to start processes on remote nodes. This is necessary because mpirun launches orted, which must be run in an environment in which the EESSI repository is mounted. If not, MPI startup will fail with an error like "error: execve(): orted: No such file or directory".

This wrapper script must be named orted, and must be located in a path that is listed in $PATH.

We placed it in ~/bin/orted, and add export PATH=$HOME/bin:$PATH to our ~/.bashrc login script.

Contents of ~/bin/orted:


# first remove path to this orted wrapper from $PATH, to avoid infinite loop
orted_wrapper_dir=$(dirname $0)
export PATH=$(echo $PATH | tr ':' '\n' | grep -v $orted_wrapper_dir | tr '\n' ':')

~/bin/ orted "$@"

Do make sure that also this orted wrapper script is executable:

chmod u+x ~/bin/orted

If not, you will likely run into an error that starts with:

An ORTE daemon has unexpectedly failed after launch ...

Slurm job script

We can use the script in a Slurm job script on Deucalion to initialize the EESSI environment in a subshell in which the EESSI CernVM-FS repository is mounted, and subsequently load the module for ESPResSo v4.2.2 and launch the Lennard-Jones fluid simulation via mpirun:

Job script (example using 2 full 48-core nodes on A64FX partition of Deucalion):

#SBATCH --ntasks=96
#SBATCH --ntasks-per-node=48
#SBATCH --cpus-per-task=1
#SBATCH --time=5:0:0
#SBATCH --partition normal-arm
#SBATCH --export=None
#SBATCH --mem=30000M
~/bin/ << EOF
source /cvmfs/
module load ESPResSo/4.2.2-foss-2023a
mpirun -np 96 python3

(the Python script is available in the EESSI test suite, see here)

EESSI promo tour @ ISC'24 (May 2024, Hamburg)

ISC logo

This week, we had the privilege of attending the ISC'24 conference in the beautiful city of Hamburg, Germany. This was an excellent opportunity for us to showcase EESSI, and gain valuable insights and feedback from the HPC community.

BoF session on EESSI

The EESSI Birds-of-a-Feather (BoF) session on Tuesday morning, part of the official ISC'24 program, was the highlight of our activities in Hamburg.

It was well attended, with well over 100 people joining us at 9am.

EESSI BoF session at ISC'24

During this session, we introduced the EESSI project with a short presentation, followed by a well-received live hands-on demo of installing and using EESSI by spinning up an "empty" Linux virtual machine instance in Amazon EC2 and getting optimized installations of popular scientific applications like GROMACS and TensorFlow running in a matter of minutes.

During the second part of the BoF session, we engaged with the audience through an interactive poll and by letting attendees ask questions.

The presentation slides, including the results of the interactive poll and questions that were raised by attendees, are available here.


During the last day of ISC'24, EESSI was present in no less than three different workshops.

RISC-V workshop

At the Fourth International workshop on RISC-V for HPC, Julián Morillo (BSC) presented our paper "Preparing to Hit the Ground Running: Adding RISC-V support to EESSI" (slides available here).

EESSI @ RISC-V workshop at ISC'24

Julián covered the initial work that was done in the scope of the MultiXscale EuroHPC Centre-of-Excellence to add support for RISC-V to EESSI, outlined the challenges we encountered, and shared the lessons we have learned along the way.

AHUG workshop

During the Arm HPC User Group (AHUG) workshop, Kenneth Hoste (HPC-UGent) gave a talk entitled "Extending Arm’s Reach by Going EESSI" (slides available here).

Next to a high-level introduction to EESSI, we briefly covered some of the challenges we encountered when testing the optimized software installations that we had built for the Arm Neoverse V1 microarchitecture, including bugs in OpenMPI and GROMACS.

EESSI @ Arm HPC User Group workshop at ISC'24

Kenneth gave a live demonstration of how to get access to EESSI and start running the optimized software installations we provide through our CernVM-FS repository on a fresh AWS Graviton 3 instance in a matter of minutes.

POP workshop

In the afternoon on Thursday, Lara Peeters (HPC-UGent) presented MultiXscale during the Readiness of HPC Extreme-scale Applications workshop, which was organised by the POP EuroHPC Centre-of-Excellence (slides available here).

EESSI @ POP workshop at ISC'24

Lara outlined the pilot use cases on which MultiXscale focuses, and explained how EESSI helps to achieve the goals of MultiXscale in terms of Productivity, Performance, and Portability.

Group picture @ POP workshop at ISC'24

At the end of the workshop, a group picture was taken with both organisers and speakers, which was a great way to wrap up a busy week in Hamburg!

Talks and demos on EESSI at exhibit

Not only was EESSI part of the official ISC'24 program via a dedicated BoF session and various workshops: we were also prominently present on the exhibit floor.

Microsoft Azure booth

Microsoft Azure invited us to give a 1-hour introductory presentation on EESSI on both Monday and Wednesday at their booth during the ISC'24 exhibit, as well as to provide live demonstrations at the demo corner of their booth on Tuesday afternoon on how to get access to EESSI and the user experience it provides.

Talk @ Microsoft Azure booth at ISC'24

Exhibit attendees were welcome to pass by and ask questions, and did so throughout the full 4 hours we were present there.

Demo @ Microsoft Azure booth at ISC'24

Both Microsoft Azure and AWS have been graciously providing resources in their cloud infrastructure free-of-cost for developing, testing, and demonstrating EESSI for several years now.

EuroHPC booth

The MultiXscale EuroHPC Centre-of-Excellence we are actively involved in, and through which the development of EESSI is being co-funded since Jan'23, was invited by the EuroHPC JU to present the goals and preliminary achievements at their booth.

Talk @ EuroHPC booth at ISC'24

Elisabeth Ortega (HPCNow!) did the honours to give the last talk at the EuroHPC JU booth of the ISC'24 exhibit.


Last but not least: we handed out a boatload free stickers with the logo of both MultiXscale and EESSI itself, as well as of various of the open source software projects we leverage, including EasyBuild, Lmod, and CernVM-FS.

Stickers at ISC'24

We have mostly exhausted our sticker collection during ISC'24, but don't worry: we will make sure we have more available at upcoming events...