Step-by-step guide
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Code execution
When using OpenMPI, binding is controlled using the –-bind-to parameter. To bind processes to cores, use --bind-to core. Possible other values can be found in the man page.
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mpirun --bind-to core ./yourprogram |
Our hardware supports hyperthreading, allowing you start 192 processes on Cascade Lake machines (*96 partitions) and 80 on Skylake machines.
If no specific requests regarding the number of tasks has been done, mpirun defaults to hyperthreading and starts cores*2 processes. If a number of tasks has been specified (with -N and/or --tasks-per-node), an (Open) mpirun honors this via the flag -map-by. For example:
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| language | bash |
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| title | Hyperthreading active, 80/192 Processes per Node will be started |
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| collapse | true |
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#!/bin/bash
#SBATCH -N 4
module load gcc/9.3.0 openmpi/gcc.9/4.1.4
cpus_per_node=${SLURM_JOB_CPUS_PER_NODE%\(*}
mpirun -map-by ppr:$cpus_per_node:node ./yourexe |
| Codeblock |
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| language | bash |
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| title | Hyperthreading disabled, 96 processes per node are started. |
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| collapse | true |
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#!/bin/bash
#SBATCH -N 4
#SBATCH --tasks-per-node 96
module load gcc/9.3.0 openmpi/gcc.9/4.1.4
tasks_per_node=${SLURM_TASKS_PER_NODE%\(*}
mpirun -map-by ppr:$tasks_per_node:node ./yourexe |