  In this paper, we analyze the performance and energy consumption of an
Arm-based high-performance computing (HPC) system developed within the European
project Mont-Blanc 3. This system, called Dibona, has been integrated by
ATOS/Bull, and it is powered by the latest Marvell's CPU, ThunderX2. This CPU
is the same one that powers the Astra supercomputer, the first Arm-based
supercomputer entering the Top500 in November 2018. We study from
micro-benchmarks up to large production codes. We include an interdisciplinary
evaluation of three scientific applications (a finite-element fluid dynamics
code, a smoothed particle hydrodynamics code, and a lattice Boltzmann code) and
the Graph 500 benchmark, focusing on parallel and energy efficiency as well as
studying their scalability up to thousands of Armv8 cores. For comparison, we
run the same tests on state-of-the-art x86 nodes included in Dibona and the
Tier-0 supercomputer MareNostrum4. Our experiments show that the ThunderX2 has
a 25% lower performance on average, mainly due to its small vector unit yet
somewhat compensated by its 30% wider links between the CPU and the main
memory. We found that the software ecosystem of the Armv8 architecture is
comparable to the one available for Intel. Our results also show that ThunderX2
delivers similar or better energy-to-solution and scalability, proving that
Arm-based chips are legitimate contenders in the market of next-generation HPC
systems.
