Problem Statement

When I run the command on my local machine, I observe a noticeable performance boost as the number of threads increases.

However, on Setonix, regardless of whether I specify 1 or 128 threads, the performance remains consistently slow and unchanged. I checked the thread count in the job output, and it does appear to spawn the correct number of threads, but the overall performance stays the same.

Local output

% ./openmp_basics 1 100000 10000 10 
Using 1 threads..

Time taken: 9.465 seconds.

% ./openmp_basics 8 100000 10000 10 
Using 8 threads..

Time taken: 2.030 seconds.

Setonix output

tail slurm-15112799.out
Using 128 threads..

Time taken: 12.112 seconds.

Here is my batch file:

#!/bin/bash

#SBATCH --account=courses0101
#SBATCH --partition=work
#SBATCH --nodes=1
#SBATCH --ntasks=1
#SBATCH --ntasks-per-node=1
#SBATCH --cpus-per-task=128
#SBATCH --mem=200G
#SBATCH --time=00:30:00


export OMP_NUM_THREADS=${SLURM_CPUS_PER_TASK}

cc -fopenmp -o openmp_basics ./openmp_basics.c
srun ./openmp_basics $OMP_NUM_THREADS 100000 10000 10

I have tried many things, still stuck here. Any idea?