WG Julien Bigot: Gysela5D, Adapting a GYrokinetic SEmi-LAgrangian code for current architectures and towards Exascale

Title : Gysela5D, Adapting a GYrokinetic SEmi-LAgrangian code for current architectures and towards Exascale

Speaker: Julien Bigot

Abstract: In order to design and operates the future reactor for nuclear fusion such as ITER (tokamaks), physicists need to better understand the various types of instabilities that develop in the plasma and impact the confinement of heat. Simulation of Ion Temperature Gradient (ITG) instabilities based on the Vlasov equations require huge amounts of computational power with a discretization of both the spacial and velocity space (6D). The gyrokinetic approximation makes this kind of simulation possible by reducing this to “only” 5D. Up to now, the semi-Lagrangian code Gysela5D has been used to perform large simulations using a few thousands cores (8k to 16k cores typically). These simulations make the hypothesis that electrons are adiabatic but recent advances seem to indicate that some instabilities could only be explained by simulating kinetic electrons. In order to do that, the spacial mesh would have to be refined by a 60³ ratio and time steps by a 60 ratio. Such simulations would require Exascale capable machines. In this talk, I present some challenges identified in order to provide an Exascale-ready code as well as solutions recently implemented and work in progress to tackle these. I especially focus on three such piece of work:

  • memory scalability optimization;
  • I/O optimizations for both checkpoints and result writing;
  • communication patterns optimization for big number of cores (Blue Gene/Q).

I will also present recent results that show that the code scales with good performance up to 1,835,008 threads (the complete Juqueen Blue Gene/Q at Jülich).

PDF: WG_150224_jbigot-gysela

WG Salem Harrache: Reconstructable Software Appliances with Kameleon

Title: Reconstructable Software Appliances with Kameleon

Speaker: Salem Harrache

Abstract: A software appliance builder bundles together an application with its needed middleware and an operating system to allow easy deployment on Infrastructure as a Service (IaaS) providers. These builders have the potential to address a key need in the computer science community: the ability to reproduce an experiment. This talk presents a software appliance builder called Kameleon that automates the construction of complex software appliances targeted at research on operating systems, HPC and distributed computing, Devops etc. It does so by proposing a highly modular description format that encourages shareability and reuse of procedures. Moreover, it provides debugging mechanisms for improving experimenter’s productivity.

PDF: WG_150127_Salem