Supercomputing

Overview

What isn’t a supercomputer

A super fast computer that just runs your program faster.

What is a supercomputer

Nibi (latest SHARCNET supercomputer)

752 computers (nodes)

140,928

662 terrabytes (TB) of RAM (most 4 gigabyte (GB)/core)

25 petabytes (PB) of SSD disk storage (home, project, and scratch)

80 petabytes (PB) of transparent tape storage (nearline)

288 NVIDIA GPUs (H100 Hopper) and 25 AMD APUs (MI300A)

200/400 gigabit (G) ethernet

How do you use a supercomputer

serial ~ (easy) many computers means you can run many programs indepedently at the same to solve many independent problems

parallel ~ (hard) many computers can (sometimes) be programmed to all collaborate and solve a single problem together

cloud ~ virtual computer on the internet (like Amazon’s Elastic Compute Cloud, Microsoft’s Azure cloud, or Google’s Compute Engine)

Canada

The players

National

Digital Research Alliannce of Canada

Regional

Compute Ontario, Calcul Québec, ACENET, BC DRI Group, and Prairies DRI

Ontario

Center for Advanced Computing (CAC), HPC4Health, SciNet, and SHARCNET

Getting an accounts

Cost

no cost

Who

faculty or those sponsored by faculty that have an account

How

https://ccdb.alliancecan.ca

apply for a Digital Research Alliance account

pick the desired regional consortia accounts

What software is available

Operating system

Linux (Rocky/AlmaLinux 9)

Programming languages

C/C++, Fortran, MATLAB/Octave, Python, R, Julia, etc.

Parallel development support

pthreads, MPI, OpenMP, CUDA, OpenACC, OpenCL

Other

common open source and commerical packages (e.g., OpenFOAM, Fluent, and STAR-CCM+)

How to use

resources are scheduled to avoid collisions and ensure fair access

access from anywhere on the internet using secure shell (SSH) to enter commands and a secure file transfer (SFTP) to transfer files

tell the supercomputer what progam (command) you want it to run and then do something else till it does it

Typical workflow

transfer your data and/or programs to the supercomputer using SFTP

login (bring up a window in which you can enter commands) to the supercomputer using SSH

enter commands to tell the scheduler what you want it to run when the required resources are avaialable

do something else until you get notification that your commands have completed running

transfer the resulting data from the supercomputer to your computer

Using

Required Software

Clusters are accessed via the secure shell programs

ssh ~ used to run commands (secure shell)

scp ~ used to copy files (secure copy)

sftp ~ alternative to copy files (secure file transfer protocol)

from anywhere on the internet using the address CLUSTER.alliancecan.ca (capitalized terms indicate you should substitute something appropriate).

Windows

Most common options are the GUI

mobaxterm [https://mobaxterm.mobatek.net/] is a good freeware GUI choice that provides everything in one package including a graphical sftp, X11 server, and local shell

PuTTY [https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html] is a basic open-source ssh-only option

Windows 10 has native versions of the command-line tools too

Windows subsystem for Linux [https://docs.microsoft.com/en-us/windows/wsl/] provides full linux text environment including secure shell

OpenSSH installable component [https://docs.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse] provides secure shell inside Windows command or power shell

MacOS X and Linux

Command-line versions are builtin and available in the shell

search for and start a terminal application

Browser

Open OnDemand (OOD) web based interface is available for some clusters

https://ondemand.sharcnet.ca

https://ondemand.scinet.utoronto.ca

Accessing

Logging in

ssh USER@CLUSTER.alliancecan.ca ~ login to CLUSTER as USER and start a remote shell session

for GUI ones (e.g., mobaxterm, putty, etc.), enter USER into username field, CLUSTER.alliancecan.ca into host name field, and connect

for web-based OOD login on web interface and choose Shell Access from the menus at the top

Copying files

scp USER@CLUSTER.alliancecan.ca:REMOTE LOCAL ~ login to CLUSTER as USER and copy REMOTE file to LOCAL file

scp LOCAL USER@CLUSTER.alliancecan.ca:REMOTE ~ login to CLUSTER as USER and copy LOCAL file to REMOTE file

for GUI ones (e.g., mobaxterm, etc.) enter USER and CLUSTER, connect, and then drag and drop files to transfer

for web-based OOD login on web interface, choose home directory, and use the upload/download button

Shell

Commands, entered interactively or ran from a file, tell computer what to do

a bit of an initial learning curve, but

much easier to automate, document, and share

Basic command

PROGRAM ARGUMENTS...

arguments usually options (switches) followed by strings (e.g., file names, etc.)

short options are a single dashes followed by letter for each switch (e.g., rm -fr mydir)

long options are a double dash followed by a descriptive string (e.g., rm --force --recurse mydir)

Help

help COMMAND ~ show help for builtin command (like “cd”)

man COMMAND ~ show the manual page for command (‘q’ to quit)

Getting around

ls ~ list files

pwd ~ what folders you are in

cd DIRECTORY ~ change to directory named directory (use “..” for previous one)

Copying/renaming/moving/removing files and directories

cp SRC DEST ~ copy file/directory (add -r for directory)

mv SRC DEST ~ move/rename file/directory

rm PATH ~ remove file (add -r for directory)

Editing files

nano PATH ~ edit file named file

Digital Research Alliance of Canada software (scientific packages)

module list ~ show what software is load environment

module avail ~ show what software you can load

module spider PACKAGE ~ search for package

module load PACKAGE ~ load package

module unload PACKAGE ~ unload the package

Running/submitting, viewing, and killing jobs

salloc ~ start interactive job

sbatch SCRIPT ~ queue batch job

squeue ~ list jobs

skill JOBID ~ kill job

Filesystems

Storage Folder

Group

Expiration

HPC

Size

Files

/home/USER

No

No

No

50GB

500K

/scratch/USER

No

60 days

Yes

20TB

1,000K

/project/PROJECT

Yes

No

Yes

1TB

500K

nibi scratch has no limit, but requires you to drop to 1TB every 60 days

quick scratch, project (default), and projects (all) links under home

Jobs

Check documentation page for desired software on docs.alliancecan.ca [https://www.docs.alliancecan.ca]

program specifc instructions

licensing details for commerical software

All significant computations (> few minutes) run as SLURM jobs

only way to access the 752 compute nodes

initial interative type-in-commands test runs with salloc

final non-interactive put-commands-in-file runs with sbatch

Batch file for sbatch have the general format

##!/bin/bash
##SBATCH OPTION1
##SBATCH OPTION2
...

COMMANDS TO RUN
...

Job options

Specify the resources and accounting required to run a job

as options to salloc and sbatch commands, and/or

in start of job files using special #SBATCH ... lines

Basic options

--account def-SPONSOR ~ account to allocate usage to

--time D-HH:MM:SS ~ maximum runtime before killing (add a bit of buffer)

--mem-per-cpu N ~ memory per CPU (suffix with K, M, G, or T for units)

Multi-threaded jobs

limited to maximum number of CPUs in one computer (generally 32)

may need export OMP_NUM_THREADS=$SLURM_CPUS_PER_TASK in job script

--cpus-per-task N ~ number of threads per process (threaded)

Multi-processor jobs (MPI)

need to start the program with the mpirun or srun commands

--ntasks ~ number of processes (MPI)

GPU jobs

--gpus-per-task TYPE:N ~ number of GPUs per process

Breakpoints

partition_stats ~ show paritioning of compute nodes eligible for jobs

Exceeding these resources decreases the number of machines that will run a job

runtime > 3, 12, 24, 72, 168, and 672hrs

memory/cpu > 12MB

OpenFOAM

Enabling

Search through the available modules to see what OpenFOAM ones exist

$ module avail openfoam

This only shows versions that are compatible with other loaded modules. All versions can be found with the spider command along with directions on what else needs to be loaded to load them

$ module spider openfoam
$ module spider openfoam/12

Load the openfoam module (not specifying a version uses the default)

$ module load openfoam

Can use the show command to see what this does

$ module show openfoam

Create the top-level user OpenFOAM directory and change to it (not strictly required, but recommended by the tutorials)

$ mkdir -p $FOAM_RUN
$ cd $FOAM_RUN

Tutorial

Copy the OpenFOAM incompressible cavity example [https://cfd.direct/openfoam/user-guide/v6-cavity] from the tutorials directory

$ cp -r $FOAM_TUTORIALS/legacy/incompressible/icoFoam/cavity/cavity .
$ cd cavity

Generate mesh

Generate the mesh data files in constant/polyMesh from the higher-level description file system/blockMeshDict

$ blockMesh

Interactive run

Run the simulation (incompressible flow using the PISO algorithm) in an interactive session to test

$ salloc --mem-per-cpu=500M --ntasks=1 --account=def-SPONSOR

$ icoFoam
$ exit

Batch run

Create a run.sh (name not important) using nano to do the same

$ nano run.sh

#!/bin/bash
#SBATCH --time=00:05:00
#SBATCH --mem-per-cpu=500M
#SBATCH --ntasks=1
#SBATCH --account=def-SPONSOR
#SBATCH --output=icoFoam-%J.log
icoFoam

Submit the batch file to the cluster to run

$ sbatch run.sh

New case

Make a new cavityMPI case based on the cavity case setup

$ cd ..
$ foamCloneCase cavity cavityMPI
$ cd cavityMPI

Run in parallel

Basic eight processor system/decomposeParDict decomposition setup

$ foamGet decomposeParDict

Edit system/decomposeParDict to be a simple (2 2 1) (4 processor) decomposition and then decompose the cavity

$ decomposePar

Run the simulation in parallel using four processors

$ salloc --mem-per-cpu=500M --ntasks=4 --account=def-SPONSOR

$ mpirun icoFoam -parallel
$ exit

Collect the output back into a single file

$ reconstructPar

Prep for ParaView

Create a NAME.foam file to give something to open in ParaView (name doesn’t matter – just identifies it as an OpenFOAM directory)

$ touch cavity.foam

Can also generate VTK input files

$ foamToVtk

ParaView

Availability

Personal

Copy data to personal machine for analysis.

Windows and OS X

Download latest version from ParaView website [https://www.paraview.org/download/]

older version may work if newer fails on older OS or graphics card

Linux

Install with your package manager (can also download as above)

Debian and Ubuntu: sudo apt-get install paraview

Fedora: sudo yum install paraview

Clusters

Remote desktop to avoid having to transfer data

Open OnDemand (OOD) (nibi, trillium)

JupyterHub (JH) (rorqual, fir)

OOD

Login and pick Compute Node -> Desktop (nibi) or Apps -> Trillium Desktop (trillium)

https://ondemand.sharcnet.ca

https://ondemand.scinet.utoronto.ca

JupyterHub

Login, start job, pick Mate Desktop or XFCE4 Desktop

https://jupyterhub.rorqual.alliancecan.ca

https://jupyterhub.fir.alliancecan.ca

Tutorial

Working through the ParaView tutorial [https://www.paraview.org/Wiki/The_ParaView_Tutorial] is one of the quickest and easiest ways to get up-to-speed on ParaView.

basic usage (what we will be going over)

batch python scripting

visualizing large models

$ cp -r /home/tyson/ParaView .

Basis of visualization

map raw data to visual data

spacial and temporal data

topology and types of grids

User interface

menu bar

tool bars

pipeline browser

properties panel

view

Basic interface

creating a source

interacting with a 3d view

modifying visualization paramaters (filter, display, view)

undo and redo (regular vs camera)

Loading data

opening file (selecting which variables to load)

representation and field coloring

scaling

Filters

selecting filters (toolbar, menu, and search)

applying a filter (contours, slices)

Multiview

creating a multiple views

linking cameras

re-arranging the views

Vector visualization

streamlines

tubes and glyphs

surface LIC

Volume rendering

Enabling

Transfer function

Plotting

histogram plot

plot over a line in space

plot over a curve

plot over time

Selections

Query and view based selections

Data vs spatial selections

Selection labels

Extract selection and spreadsheet

Index

Table of Contents

Super Computing

Overview

What isn’t a supercomputer

What is a supercomputer

How do you use a supercomputer

Canada

The players

Getting an accounts

What software is available

How to use

Typical workflow

Using

Required Software

Windows

MacOS X and Linux

Accessing

Logging in

Copying files

Shell

Basic command

Filesystems

Jobs

Job options

Breakpoints

OpenFOAM

OpenFOAM

Enabling

Tutorial

Generate mesh

Interactive run

Batch run

New case

Run in parallel

Prep for ParaView

ParaView

VDI nodes

Accessing

Software

ParaView

Personal computer

VDI

Tutorial

Basis of visualization

User interface

Basic interface

Loading data

Filters

Multiview

Vector visualization

Volume rendering

Plotting

Selections

Exercises

OpenFOAM

Cavity

Dam break

ParaView

OpenFOAM

Cavity

double the resolution

Dam break

copy the dam break tutorial and run it on the cluster (up to post-processing)

https://cfd.direct/openfoam/user-guide/v6-dambreak/

do a parallel run (running in parallel section – increasing resolution is optional)

ParaView

extracting just girder

extracting a plane

glyphs

graphs (multiple displays)

plot over line

plot over time (sample data)

enabling LIC plugin and showing on plane

clipping off the sides

enabling volume rendering for low pressure regions

stream tracers, tubes, and glyphs