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workaround for cxil_map write error #161

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Merged
merged 7 commits into from
Jun 30, 2025
Merged

workaround for cxil_map write error #161

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267e746
workaround for cxil_map write error
simonpintarelli Jun 18, 2025
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Merge branch 'main' into cxil_map-write-error
bcumming Jun 20, 2025
d741d52
Update docs/software/communication/cray-mpich.md
simonpintarelli Jun 30, 2025
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update
simonpintarelli Jun 30, 2025
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Merge branch 'cxil_map-write-error' of github.com:eth-cscs/cscs-docs …
simonpintarelli Jun 30, 2025
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Update docs/software/communication/cray-mpich.md
simonpintarelli Jun 30, 2025
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Merge branch 'main' into cxil_map-write-error
bcumming Jun 30, 2025
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13 changes: 11 additions & 2 deletions docs/software/communication/cray-mpich.md
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Expand Up @@ -79,12 +79,21 @@ Cray MPICH may sometimes hang on larger runs.

Performance may be negatively affected by this option.

#### `"cxil_map: write error"` when doing inter-node GPU-aware MPI communication

This error message is sometimes triggered by applications that use GPU Direct MPI calls when they trigger a bug in gdrcopy (a low-level library used to copy buffers between GPUs).
Setting the following option will completely disable gdrcopy.
Note that this has a performance impact for small message sizes, so it should only be enabled on a case-by-case basis.
```bash
export FI_CXI_SAFE_DEVMEM_COPY_THRESHOLD=0
```

### Resolved issues

#### `"cxil_map: write error"` when doing inter-node GPU-aware MPI communication

??? info "The issue has been resolved on the 7th of October 2024 with a system update"
The issue was caused by a system misconfiguration.
??? info "The issue has been resolved on the 7th of October 2024 with a system
update" The issue was caused by a system misconfiguration.

When doing inter-node GPU-aware communication with Cray MPICH after the update on the 30th of September 2024 on Alps, applications will fail with:
```bash
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