| Issue |
123092
|
| Summary |
[AMDGPU][Attributor] OpenMC Performance Regression on AMD GPU
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
jtramm
|
I have observed a performance regression in the OpenMC scientific simulation application (which uses OpenMP target offloading) on the AMD MI250 due to commit https://github.com/llvm/llvm-project/commit/7dbd6cd2946ec3a9b4ad2dfd7ead177baac15bd7, which is part of PR #114357. The regression is not observed on NVIDIA GPUs.
This commit causes OpenMC to be 20% slower overall on a typical benchmark problem, with the most expensive kernel in the simulation being about 2x slower.
OpenMC can be installed and its performance benchmark run using the following script: https://github.com/jtramm/openmc_offloading_builder/tree/main
FOM before this commit (higher is better):
```
Calculation Rate (inactive) = 239870.0 particles/second
```
FOM after this commit:
```
Calculation Rate (inactive) = 192707.0 particles/second
```
Main kernel timing before this commit:
```
XS lookups (Fuel) = 1.8720e+01 seconds
```
Main kernel after this commit:
```
XS lookups (Fuel) = 3.5231e+01 seconds
```
Rocprof shows similar slowdown for this kernel, which it lists as:
```
__omp_offloading_25_7c638f81__ZN6openmc32process_calculate_xs_events_fuelEv_l256.kd
```
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