[Perf] Linux/arm64: 2 Regressions on 8/13/2026 7:09:48 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | ubuntu 22.04
Queue | AmpereUbuntu
Baseline | [63ae268826a5091dfc89baa49844df1aed874a95](https://github.com/dotnet/runtime/commit/63ae268826a5091dfc89baa49844df1aed874a95)
Compare | [691fd960eb500743b4be71373b11b2263bdbc318](https://github.com/dotnet/runtime/commit/691fd960eb500743b4be71373b11b2263bdbc318)
Diff | [Diff](https://github.com/dotnet/runtime/compare/63ae268826a5091dfc89baa49844df1aed874a95...691fd960eb500743b4be71373b11b2263bdbc318)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.IO.Tests.Perf_FileStream

Benchmark | Baseline | Test | Test/Base | Test Quality | Edge Detector | Baseline IR | Compare IR | IR Ratio
-- | -- | -- | -- | -- | -- | -- | -- | --
|

• [LockUnlock - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 11.50 μs | 14.19 μs | 1.23 | 0.74 | False | | |
|

• [SeekForward - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 11.82 μs | 12.80 μs | 1.08 | 0.39 | False | | |

![graph]()
![graph]()
[Test Report]()

### Repro
General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

```cmd
git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.IO.Tests.Perf_FileStream*'
```

### System.IO.Tests.Perf_FileStream.LockUnlock(fileSize: 1024, options: Asynchronous)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.IO.Tests.Perf_FileStream.SeekForward(fileSize: 1024, options: None)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

[Profiling workflow for dotnet/runtime repository](https://github.com/dotnet/performance/blob/master/docs/profiling-workflow-dotnet-runtime.md)
[Benchmarking workflow for dotnet/runtime repository](https://github.com/dotnet/performance/blob/master/docs/benchmarking-workflow-dotnet-runtime.md)

Start with the linked benchmark source at src/benchmarks/micro/libraries/System.IO.FileSystem/Perf.FileStream.cs, especially LockUnlock and SeekForward, then run the provided benchmarks_ci.py command for System.IO.Tests.Perf_FileStream. Compare the results with the baseline and report or resolve the two arm64 Ubuntu regressions shown in the test report.

Written by the indexing model from the issue text.