[ET Trac] #2756: SystemTopology fails to handle Intel CPUs with performance and efficiency cores

[Roland Haas]

#2756: SystemTopology fails to handle Intel CPUs with performance and efficiency cores

 Reporter: Roland Haas
   Status: new
Milestone: 
  Version: 
     Type: bug
 Priority: major
Component: EinsteinToolkit thorn

SystemTopology fails on new Intel CPUs with an assert similar to:

```
cactus_sim: configs/sim/build/SystemTopology/system_topology.cc:471: void {anonymous}::set_bindings(hwloc_topology_t, const mpi_host_mapping_t&): Assertion `num_pus % num_cores == 0' failed.
```

where in the case of a  12th Gen Intel\(R\) Core\(TM\) i7-12700

[https://en.wikipedia.org/wiki/List\_of\_Intel\_Core\_i7\_processors#Golden\_Cove\_\+\_Gracemont\_microarchitecture\_\(12th\_generation\)](https://en.wikipedia.org/wiki/List_of_Intel_Core_i7_processors#Golden_Cove_+_Gracemont_microarchitecture_(12th_generation))

with performance \(16\) and efficiency \(4\) logical cpus hwloc reports:

core\_depth 5  
num\_cores 12  
pu\_depth 6  
num\_pus 20

and the assert \`num\_pus % num\_cores == 0\` fails \(b/c only the 8 performance  
cores have hyperthreads\).

This has been reported on the mailing list in [https://lists.einsteintoolkit.org/pipermail/users/2023-August/009036.html](https://lists.einsteintoolkit.org/pipermail/users/2023-August/009036.html)

Not sure if the asserted property is indeed required by SystemTopology or if this is only a sanity check that can be removed without affecting functionality. Certainly performance will be unbalanced between MPI ranks and OpenMP threads that run on P or E cores respectively \(and also if a hyperthread pair was split among two MPI ranks\).

This may mostly affect workstations and laptops as I would not expect server class CPUs \(on HPC systems\) to have efficiency cores \(do they?\).

--
Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2756/systemtopology-fails-to-handle-intel-cpus
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