Leibniz hardware

Leibniz was installed in the spring of 2017. It is a NEC system consisting of 152 nodes with 2 14-core Intel E5-2680v4 Broadwell generation CPUs connected through a EDR InfiniBand network. 144 of these nodes have 128 GB RAM, the other 8 have 256 GB RAM. The nodes do not have a sizeable local disk. The cluster also contains a node for visualisation and 3 node types for experimenting with accelerator: 2 nodes for GPU computing (NVIDIA Pascal generation), one node with dual NEC SX-Aurora TSUBASA vector processors and one node with an Intel Xeon Phi expansion board.

Access restrictions

Access is available for faculty, students (master’s projects under faculty supervision), and researchers of the AUHA. The cluster is integrated in the VSC network and runs the standard VSC software setup. It is also available to all VSC-users, though we appreciate that you contact the UAntwerpen support team so that we know why you want to use the cluster.

Jobs can have a maximal execution wall time of 3 days (72 hours), except on the “hopper” compute nodes of Leibniz were it is possible to submit 7 days jobs on request (motivation needed).

Please also consider using the newer cluster Vaughan for big parallel jobs that can use 64 cores or multiples thereof as soon as that cluster becomes available.

The login nodes and regular compute nodes are freely available. Contact UAntwerp user support (hpc@uantwerpen.be) for access to the visualization node and accelerator nodes (free of charge but controlled access).

Hardware details

The nodes are connected using an InfiniBand EDR network except for the “hopper” compute nodes that utilize FDR10 InfiniBand. More info on the storage system is available on the UAntwerpen storage page.

Login infrastructure

Direct login is possible to both login nodes and to the visualization node.

  • From outside the VSC network: use the external interface names. Outside of Belgium, a VPN connection to the UAntwerp network is required.
  • From inside the VSC network (e.g., another VSC cluster): use the internal interface names.
External interface Internal interface
Login generic login-leibniz.hpc.uantwerpen.be
Login login1-leibniz.hpc.uantwerpen.be ln1.leibniz.antwerpen.vsc login1.leibniz.antwerpen.vsc
login2-leibniz.hpc.uantwerpen.be ln2.leibniz.antwerpen.vsc login2.leibniz.antwerpen.vsc
Visualisation node viz1-leibniz.hpc.uantwerpen.be viz1.leibniz.antwerpen.vsc

Characteristics of the compute nodes

To remain compatible with the typical VSC setup, a number of properties can be used in job scripts. However, only one is really useful in the current setup of leibniz to select the proper node type, mem256.

property explanation
broadwell only use Intel processors from the Broadwell family (E5-XXXXv4) (Not needed at the moment as this is CPU type is selected automatically)
ivybridge only use Intel processors from the Ivy Bridge family (E5-XXXXv2) Not needed at the moment as there is no automatic selection of the queue for the Ivy Bridge nodes. Specify -q hopper instead.
gpu only use the GPGPU nodes of Leibniz. Not needed at the moment as there is no automatic selection of the queue for the GPGPU nodes at the moment. Specify -q gpu instead.
ib use InfiniBand interconnect (Not needed at the moment as all nodes are connected to the InfiniBand interconnect)
mem128 use nodes with 128 GB RAM (roughly 112 GB available). This is the majority of the nodes on Leibniz. Requesting this as a feature ensures that you get a node with 128 GB of memory and keep the nodes with more memory available for other users who really need that feature.
mem256 use nodes with 256 GB RAM (roughly 240 GB available). This property is useful if you submit a batch of jobs that require more than 4 GB of RAM per processor but do not use all cores and you do not want to use a tool to bundle jobs yourself such as Worker, as it helps the scheduler to put those jobs on nodes that can be further filled with your jobs.

Compiling for Leibniz

To compile code for Leibniz, all intel, foss and GCC modules can be used (the latter equivalent to foss but without MPI and the math libraries).

Optimization options for the Intel compilers

To optimize specifically for Leibniz, compile on one of the Leibniz login or compute nodes and combine the option -xHost with either optimization level -O2 or -O3. For some codes, the additional optimizations at level -O3 actually produce slower code (often the case if the code contains many short loops).

Note that if you forget these options, the default for the Intel compilers is to generate code at optimization level -O2 (which is pretty good) but for the Pentium 4 (-march=pentium4) which uses none of the new instructions and hence also none of the vector instructions introduced since 2005, which is pretty bad. Hence always specify -xHost (or any of the equivalent architecture options specifically for Broadwell for specialists) when compiling code.

Optimization options for the GNU compilers

Never use the default GNU compilers installed on the system, but always load one of the foss or GCC modules.

To optimize for Leibniz, compile on one of the Leibniz login or compute nodes and combine either the option -march=native or -march=broadwell with either optimization level -O2 or -O3. In most cases, and especially for floating point intensive code, -O3 will be the preferred optimization level with the GNU compilers as it only activates vectorization at this level whereas the Intel compilers already offer vectorization at level -O2.

Note that if you forget these options, the default for the GNU compilers is to generate unoptimized (level -O0) code for a very generic CPU (-march=x86-64) which doesn’t exploit the performance potential of the Leibniz CPUs at all. Hence one should always specify an appropriate architecture (the -march flag) and appropriate optimization level (the -O flag) as explained in the previous paragraph.

Origin of the name

Leibniz is named after Gottfried Wilhelm Leibniz, a German multi-disciplinary scientist living in the late 17th and early 18th century. Leibniz may be best known as a developer of differential and integral calculus, independently of the work of Isaac Newton. But his contributions to science do not stop there. Leibniz also refined the binary number system, the foundation of nearly all modern computers. He also designed mechanical calculators on which one could do the four basic operations (add, subtract, multiply and divide). In all, Leibniz made contributions to philosophy, mathematics, physics and technology, and several other fields.