# Number of threads assigned via SLURM

**URL:** <https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820>\
**Category:** Specific Domains\
**Tags:** hpc, slurm\
**Created:** [April 22, 2026, 12:30am UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820 "2026-04-22T00:30:57Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![pulk\_jain](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pulk_jain/32/204900_2.png) [@pulk\_jain](https://discourse.julialang.org/u/pulk_jain)\
**Post date:** [April 22, 2026, 12:30am UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820/1 "2026-04-22T00:30:57Z")

</div>

I am trying to run some multi-threaded code on a cluster using SLURM.

```julia-auto
#SBATCH --cpus-per-task=4
JPATH=$HOME/.juliaup/bin
export JULIA_DEPOT_PATH="/my/storage/dir/.julia:"
export JULIA_NUM_THREADS=auto
$JPATH/julia main_0_test.jl

```

Using ThreadPinning.jl, I pin the threads according to affinity mask and then check `threadinfo` with `slurm=true`.

```julia-auto
Hostname: r184.ib.bridges2.psc.edu
CPU(s): 2 x AMD EPYC 7742 64-Core Processor
CPU target: znver2
Cores: 128 (128 CPU-threads)
NUMA domains: 2 (64 cores each)

SLURM: 2 assigned CPU-threads. Will only show those below.

Julia threads: 4

CPU socket 1
  4,5

# = Julia thread, # = >1 Julia thread

(Mapping: 1 => 124, 2 => 125, 3 => 126, 4 => 127,)
Threads.nthreads() = 4

```

I am confused as to why it says slurm only assigned 2 cpu threads. Number of Julia threads are correct, and the mapping also shows where they have been assigned. The computations also run faster as I increase the number of cpus requested. I am wondering what does the “2 assigned CPU-threads” mean and if it will lead to collisions when running multiple jobs. Would it be better to ask these questions to the team running the clusters instead?

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<div class="post-metadata">

**Author:** ![NonDairyNeutrino](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nondairyneutrino/32/221496_2.png) [@NonDairyNeutrino](https://discourse.julialang.org/u/NonDairyNeutrino)\
**Post date:** [April 22, 2026, 2:19am UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820/2 "2026-04-22T02:19:21Z")

</div>

My first thought would be that the chip has hyperthreads (or whatever the AMD equivalent is), so Julia pins its 4 threads to 4 logical cores over 2 physical cores and SLURM only allocates or sees the 2 physical. But that’s a complete guess as I’m mostly unfamiliar with SLURM.

Is the program using SlurmClusterManager.jl?

---

<div class="post-metadata">

**Author:** ![pulk\_jain](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pulk_jain/32/204900_2.png) [@pulk\_jain](https://discourse.julialang.org/u/pulk_jain)\
**Post date:** [April 22, 2026, 3:50pm UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820/3 "2026-04-22T15:50:04Z")

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Even when I run with more threads, I get the same slurm message. For example with 16 threads:

```julia-auto
Hostname: r200.ib.bridges2.psc.edu
CPU(s): 2 x AMD EPYC 7742 64-Core Processor
CPU target: znver2
Cores: 128 (128 CPU-threads)
NUMA domains: 2 (64 cores each)

SLURM: 2 assigned CPU-threads. Will only show those below.

Julia threads: 16

CPU socket 1
  4,5

# = Julia thread, # = >1 Julia thread

(Mapping: 1 => 94, 2 => 95, 3 => 96, 4 => 97, 5 => 98, ...)
Threads.nthreads() = 16

```

I am not using SlurmCluserManager, the use case seemed more applicable towards distributed computing and I didn’t look further into it.

---

<div class="post-metadata">

**Author:** ![carstenbauer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/carstenbauer/32/4981_2.png) [@carstenbauer](https://discourse.julialang.org/u/carstenbauer)\
**Post date:** [April 23, 2026, 4:35am UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820/4 "2026-04-23T04:35:33Z")

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How many cpu(-thread)s are you requesting through SLURM? What does your job script look like, especially the SLURM parameters at the top of it?

---

<div class="post-metadata">

**Author:** ![pulk\_jain](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pulk_jain/32/204900_2.png) [@pulk\_jain](https://discourse.julialang.org/u/pulk_jain)\
**Post date:** [April 23, 2026, 9:15pm UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820/5 "2026-04-23T21:15:36Z")

</div>

Earlier I was asking for a certain number of cpus through `cpus-per-task` command. Now I am using `n` instead. Here is the full .sh file:

```julia-auto
#!/bin/bash
#SBATCH --job-name=mu_0_multi_0.1_4
#SBATCH -p RM-shared
#SBATCH -N 1
#SBATCH -n 12
##SBATCH --cpus-per-task=8
#SBATCH --time=72:00:00
#SBATCH --output=%x.out
#SBATCH --error=%x.err
#SBATCH --mail-type=END,FAIL
echo "starting $SLURM_JOBID at `date` on `hostname`"

JPATH=$HOME/.juliaup/bin
echo "julia obtained from $JPATH"
export JULIA_DEPOT_PATH="/project_path/.julia:"
export JULIA_NUM_THREADS=auto

$JPATH/julia main_multi_0_1_4.jl

echo "ended at `date` on `hostname`"

exit 0

```

Running `getcpuids()`, `pinthreads(:affinitymask)` and then `threadinfo()` inside the script:

```julia-auto
Hostname: r040.ib.bridges2.psc.edu
CPU(s): 2 x AMD EPYC 7742 64-Core Processor
CPU target: znver2
Cores: 128 (128 CPU-threads)
NUMA domains: 2 (64 cores each)

SLURM: 8 assigned CPU-threads. Will only show those below.

Julia threads: 12

CPU socket 1
  38,39,41,58,59,60,61,62

# = Julia thread, # = >1 Julia thread

(Mapping: 1 => 52, 2 => 53, 3 => 54, 4 => 55, 5 => 85, ...)

```

For some reason, Slurm seems to have assigned 8 cpu-threads even when I have asked for 12 threads. The ids obtained from getcpuids and the ones that get pinned also do not match. I am using `JULIA_NUM_THREADS=auto`, and the number of threads initialized do match the number of cpus requested.  
I do not get consistent speeds with different instances of the job. Some run fast, and some slow while the architecture of each node is same and I have asked for the same number of threads.

---

<div class="post-metadata">

**Author:** ![carstenbauer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/carstenbauer/32/4981_2.png) [@carstenbauer](https://discourse.julialang.org/u/carstenbauer)\
**Post date:** [April 24, 2026, 4:50am UTC](https://discourse.julialang.org/t/number-of-threads-assigned-via-slurm/136820/6 "2026-04-24T04:50:26Z")

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> [@pulk\_jain](#):
>
> For some reason, Slurm seems to have assigned 8 cpu-threads even when I have asked for 12 threads.

This is strange. Is there some SLURM output regarding this in the job log file? I’d focus on figuring out what’s going on here before doing anything Julia-related.

> [@pulk\_jain](#):
>
> The ids obtained from getcpuids and the ones that get pinned also do not match.

This is also weird. Normally you shouldn’t be able to use CPU-threads that aren’t part of your SLURM allocation. (Again, not really a Julia issue.)

Perhaps you should talk to the Cluster admins/support team.