modules

Modules and Compilers on Isambard

Both Isambard-AI and Isambard 3 are HPE/Cray systems and use the Cray Programming Environment for managing compilers, MPI, and scientific libraries through a modular software system.

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Module Commands

Command	Effect
module avail	List all available modules
module load <name>	Load a module into the current session
module unload <name>	Unload a module from the current session
module list	List all currently loaded modules
module purge	Unload all loaded modules
module spider <name>	Search for a module and show details

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BriCS-Supplied Modules

BriCS provides the following utility modules (available on AIP1, AIP2, and Isambard 3 unless noted):

Module	Description
brics/default	Default user environment (loaded automatically)
brics/userenv	Sets $LOCALDIR, $SCRATCHDIR, and $TMPDIR — see the storage docs
brics/emacs	Emacs text editor
brics/nano	nano text editor
brics/tmux	tmux terminal multiplexer — reload the module when restarting a terminal; sessions persist
brics/nccl	Required for multi-node GPU workflows. Provides NCCL (built against libfabric) and the NCCL AWS-OFI plugin for Slingshot high-speed network support
brics/apptainer-multi-node	Support for multi-node Apptainer jobs — see the Apptainer multi-node docs

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Programming Environments

Available environments

module av PrgEnv           # quick list
module spider PrgEnv       # detailed view

PrgEnv-cray/8.5.0    PrgEnv-gnu/8.5.0

PrgEnv-gnu is recommended — good performance, familiar behaviour, all dependencies loaded automatically:

module load PrgEnv-gnu
module list
# Loads: brics/userenv, brics/default, gcc-native/13.2, craype, craype-arm-grace,
#        libfabric, craype-network-ofi, cray-libsci, cray-mpich, PrgEnv-gnu

Key components loaded by PrgEnv-gnu:

Module	Purpose
gcc-native/13.2	GCC 13.2 compiler suite
libfabric	Communication library for Slingshot 11 high-speed interconnect
cray-libsci	Scientific and math libraries (BLAS, LAPACK, etc.)
cray-mpich	MPI libraries

Cray compiler wrappers

With a PrgEnv loaded, use the Cray compiler wrappers rather than invoking GCC directly:

Wrapper	Language	GCC equivalent
cc	C	gcc
CC	C++	g++
ftn	Fortran	gfortran

The wrappers automatically link to loaded Cray PE libraries (MPI, LibSci, etc.). Do not mix wrapper commands and raw GCC commands in the same build.

To see exactly what the wrapper passes to the underlying compiler:

ftn -craype-verbose -o hello hello.f90
# Shows full flags, include paths, and linked libraries

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Compiler Options

Targeting the NVIDIA Grace Superchip (Arm Neoverse V2)

Use -mcpu=neoverse-v2 to target the Grace CPU architecture. Note this differs from x86 (-march):

cc -mcpu=neoverse-v2 -O3 mycode.c -o mycode

For further tuning guidance see the NVIDIA Grace Performance Tuning Guide.

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NVIDIA Compilers

Load just the NVIDIA compiler suite (without a full programming environment):

module load nvidia
nvc --version      # C
nvc++ --version    # C++
nvfortran --version
# All target: linuxarm64, aarch64, neoverse-v2

Note: Loading only module load nvidia does not load MPI libraries automatically. For MPI, load a full PrgEnv instead, or see the MPI guide.

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Profiling Tools

gprof

Available without loading any modules:

gprof ./a.out

Cray Perftools

module load perftools-base
pat_run ./a.out

Full docs: HPE Cray Performance Tools

NVIDIA Nsight Systems

module load cudatoolkit
nsys profile ./a.out

Full docs: NVIDIA Nsight Systems User Guide

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Quick Reference

Goal	Command
Recommended build environment	module load PrgEnv-gnu
Compile C	cc -mcpu=neoverse-v2 -O3 myfile.c
Compile C++	CC -mcpu=neoverse-v2 -O3 myfile.cpp
Compile Fortran	ftn -mcpu=neoverse-v2 -O3 myfile.f90
Debug wrapper flags	cc -craype-verbose ...
Multi-node GPU jobs	module load brics/nccl
Profile with Cray tools	module load perftools-base → pat_run
Profile with NVIDIA tools	module load cudatoolkit → nsys
Spack builds	See Spack guide for compiler config

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Related Resources

• Isambard MPI guide
• Isambard Spack guide
• Cray Programming Environment docs
• NVIDIA Grace Performance Tuning Guide