Integrating LHCb workflows on HPC resources: status and strategies

High Performance Computing (HPC) supercomputers are expected to play an increasingly important role in HEP computing in the coming years. While HPC resources are not necessarily the optimal fit for HEP workflows, computing time at HPC centers on an opportunistic basis has already been available to the LHC experiments for some time, and it is also possible that part of the pledged computing resources will be offered as CPU time allocations at HPC centers in the future. The integration of the experiment workflows to make the most efficient use of HPC resources is therefore essential. This paper describes the work that has been necessary to integrate LHCb workflows at a specific HPC site, the Marconi-A2 system at CINECA in Italy, where LHCb benefited from a joint PRACE (Partnership for Advanced Computing in Europe) allocation with the other Large Hadron Collider (LHC) experiments. This has required addressing two types of challenges: on the software application workloads, for optimising their performance on a many-core hardware architecture that differs significantly from those traditionally used in WLCG (Worldwide LHC Computing Grid), by reducing memory footprint using a multi-process approach; and in the distributed computing area, for submitting these workloads using more than one logical processor per job, which had never been done yet in LHCb.Comment: 9 pages, submitted to CHEP2019 proceedings in EPJ Web of Conference

On Usage Control for Data Grids: Models, Architectures, and Specifications

This thesis reasons on usage control in Data Grids, by presenting models, architectures and specifications. This work is a step toward a continuous monitoring and control of the data access and usage in a Data Grid. First, the thesis presents a background on Grids, security, and security for Grids, by making an abstraction to the current Grid implementations. We argue that usage control in Data Grids should be considered as a process composed by two black boxes. We analysed the requirements for Grid security, and propose a distributed usage control model suitable for Grids and distributed systems alike. Then, we apply such model to a Data Grid abstraction, and present a usage control architecture for Data Grids that uses the functional components of the currents Grids. We also present an abstract specification for an enforcing mechanism for usage control policies. To do so, we use a formal requirement engineering methodology with a bottom-up approach, that proves that the specification is sound and complete. With the methodology, we show formally that such abstract specification can enforce all the different typologies of usage control policies. Finally, we consider how existing prototypes can fit in the proposed architecture, and the advantages derived from using Semantic Grid techologies for the specification of policies subjects and objects

A Subset of the CERN Virtual Machine File System: Fast Delivering of Complex Software Stacks for Supercomputing Resources

Delivering a reproducible environment along with complex and up-to-date software stacks on thousands of distributed and heterogeneous worker nodes is a critical task. The CernVM-File System (CVMFS) has been designed to help various communities to deploy software on worldwide distributed computing infrastructures by decoupling the software from the Operating System. However, the installation of this file system depends on a collaboration with system administrators of the remote resources and an HTTP connectivity to fetch dependencies from external sources. Supercomputers, which offer tremendous computing power, generally have more restrictive policies than grid sites and do not easily provide the mandatory conditions to exploit CVMFS. Different solutions have been developed to tackle the issue, but they are often specific to a scientific community and do not deal with the problem in its globality. In this paper, we provide a generic utility to assist any community in the installation of complex software dependencies on supercomputers with no external connectivity. The approach consists in capturing dependencies of applications of interests, building a subset of dependencies, testing it in a given environment, and deploying it to a remote computing resource. We experiment this proposal with a real use case by exporting Gauss-a Monte-Carlo simulation program from the LHCb experiment-on Mare Nostrum, one of the top supercomputers of the world. We provide steps to encapsulate the minimum required files and deliver a light and easy-to-update subset of CVMFS: 12.4 Gigabytes instead of 5.2 Terabytes for the whole LHCb repository

A singular case of cavernous internal carotid artery aneurysm in patient with cavernous sinus syndrome and bacterial meningitis

AbstractWe report the uncommon case of an acute cavernous sinus syndrome in a patient who was consequently discovered to have both a cavernous internal carotid artery aneurysm and bacterial meningitis. Which came first, the chicken or the egg? Which of the two, the aneurysm or the meningitis, gave rise to the patient’s symptoms? We briefly reviewed the literature of similar cases and tried to analyze the possible pathophysiological relationship between these findings. Moreover, this case highlights the importance of a multidisciplinary management of these patients to better decide between a medical and a surgical and/or endovascular treatment

A VLBI experiment using a remote atomic clock via a coherent fibre link

We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks

Comparing Remote Atomic Clocks via VLBI Networks and Fiber Optic Links: the LIFT/MetGeSp Perspective

Very Long Baseline Interferometry experiments require an extremely precise synchronization between the atomic clocks keeping the time and frequency standards at radiotelescope observatories. Recently the availability of fiber optic links from a few radio observatories and their national metrological institutes has made the streaming of extremely stable frequency standards via optical atomic clocks possible (even two orders of magnitudes better than Rubidium or Hydrogen maser standards). Firstly, we present the infrastructure of the Italian Link for Frequency and Time (LIFT) and results of the MetGeSp project aimed at finally creating a common clock between two of the antennas of the VLBI Italian Network. Secondly, the results are shown from VLBI experiments in which the rms phase noise was used to accurately compare the synchronicity of atomic clocks located at a few European stations (Medicina, Noto, Yebes, Torun, and Matera). VLBI clock timing proves a valid alternative to satellite-based techniques such as the Global Navigation Satellite System or the Two-Way Satellite Time and Frequency Transfer

The First Geodetic VLBI Field Test of LIFT: a 550-km-long Optical Fiber Link for Remote Antenna Synchronization

We present the first field test of the implementation of a coherent optical fiber link for remote antenna synchronization realized in Italy between the Italian Metrological Institute (INRIM) and the Medicina radio observatory of the National Institute for Astrophysics (INAF). The Medicina VLBI antenna participated in the EUR137 experiment carried out in September 2015 using, as reference systems, both the local H-maser and a remote H-maser hosted at the INRIM labs in Turin, separated by about 550 km. In order to assess the quality of the remote clock, the observed radio sources were split into two sets, using either the local or the remote H-maser. A system to switch automatically between the two references was integrated into the antenna field system. The observations were correlated in Bonn and preliminary results are encouraging since fringes were detected with both time references along the full 24 hours of the session. The experimental set-up, the results, and the perspectives for future radio astronomical and geodetic experiments are presented

Optical Fiber Links Used in VLBI Networks and Remote Clock Comparisons: the LIFT/MetGesp Project

The synchronization between atomic clocks plays an important part in both radio astronomical and geodetic Very Long Baseline Interferometry, as the clocks are responsible for providing time and frequency reference at radio stations. The availability of highly stable optical fiber links from a few radio observatories and their national metrological institutes has recently allowed the streaming of frequencies from optical clocks based on the Sr/Yb lattice technology (even two order of magnitudes more stable than H-maser clocks). We will present the current status of the Italian Link for Frequency and Time (LIFT) and the ongoing e orts to realize a geodetic experiment utilizing the radio stations in Medicina and Matera connected in common clock via the optical fiber link. We will then show the results from the latest VLBI clock timing experiments also making use of the LIFT link to compare atomic clocks of the three italian radio VLBI antennas (Mc, Sr and Nt) using the rms noise in the interferometric phase. VLBI clock timing proves more e ective than Global Navigation Satellite System and less expensive than Two-Way Satellite Frequency and Time Transfer in synchronizing remote clocks

A Coherent Optical Fiber Link for Very Long Baseline Interferometry

We realize a phase-stabilised optical fiber backbone that connects the Italian National Metrology Institute with two radio telescopes over a 600 km baseline. This allows referencing of Very Long Baseline Interferometry (VLBI) facilities with the best atomic frequency standards available today and the implementation of a common-clock architecture, which we are now using to assess VLBI ultimate performances