Merge branch '476-fix-remeo-smt' into 'preview'

Resolve "Romeo SMT enabled by default?"

Closes #476

See merge request !821

doc.zih.tu-dresden.de/docs/jobs_and_resources/alpha_centauri.md

@@ -12,6 +12,14 @@ The hardware specification is documented on the page
     The NVIDIA A100 GPUs may only be used with **CUDA 11** or later. Earlier versions do not
     recognize the new hardware properly. Make sure the software you are using is built with CUDA11.
 
+There is a total of 48 physical cores in each node. SMT is also active, so in total, 96 logical
+cores are available per node.
+
+!!! note
+
+        Multithreading is disabled per default in a job.
+        See the [Slurm page](slurm.md) on how to enable it.
+
 ### Modules
 
 The easiest way is using the [module system](../software/modules.md).

doc.zih.tu-dresden.de/docs/jobs_and_resources/hardware_overview.md

@@ -26,7 +26,7 @@ users and the ZIH.
 
 - 34 nodes, each with
     - 8 x NVIDIA A100-SXM4 Tensor Core-GPUs
-    - 2 x AMD EPYC CPU 7352 (24 cores) @ 2.3 GHz, Multithreading disabled
+    - 2 x AMD EPYC CPU 7352 (24 cores) @ 2.3 GHz, Multithreading available
     - 1 TB RAM
     - 3.5 TB local memory on NVMe device at `/tmp`
 - Hostnames: `taurusi[8001-8034]`
@@ -36,7 +36,7 @@ users and the ZIH.
 ## Island 7 - AMD Rome CPUs
 
 - 192 nodes, each with
-    - 2 x AMD EPYC CPU 7702 (64 cores) @ 2.0 GHz, Multithreading enabled,
+    - 2 x AMD EPYC CPU 7702 (64 cores) @ 2.0 GHz, Multithreading available
     - 512 GB RAM
     - 200 GB local memory on SSD at `/tmp`
 - Hostnames: `taurusi[7001-7192]`

doc.zih.tu-dresden.de/docs/jobs_and_resources/slurm.md

@@ -316,6 +316,32 @@ provide a comprehensive collection of job examples.
     * Submisson: `marie@login$ sbatch batch_script.sh`
     * Run with fewer MPI tasks: `marie@login$ sbatch --ntasks=14 batch_script.sh`
 
+## Using Simultaneous Multithreading (SMT)
+
+Most modern architectures offer simultaneous multithreading (SMT), where physical cores of a CPU are
+split into virtual cores (aka. threads). This technique allows to run two instruction streams per
+physical core in parallel.
+
+At ZIH systems, SMT is available at the partitions `rome` and `alpha`. It is deactivated by
+default, because the environment variable `SLURM_HINT` is set to `nomultithread`.
+If you wish to make use of the SMT cores, you need to explicitly activate it.
+In principle, there are two different ways:
+
+1. Change the value of the environment variable via `export SLURM_HINT=multithread` in your current
+   shell and submit your job file, or invoke your `srun` or `salloc` command line.
+
+1. Clear the environment variable via `unset SLURM_HINT` and provide the option `--hint=multithread`
+   to `sbatch`, `srun` or `salloc` command line.
+
+??? warning
+
+     If you like to activate SMT via the directive
+     ```
+     #SBATCH --hint=multithread
+     ```
+     within your job file, you also have to clear the environment variable `SLURM_HINT` before
+     submitting the job file. Otherwise, the environment varibale `SLURM_HINT` takes precedence.
+
 ## Heterogeneous Jobs
 
 A heterogeneous job consists of several job components, all of which can have individual job