[Perf] Linux/arm64: 1 Regression on 7/27/2026 11:29:43 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | azurelinux 3.0
Queue | CobaltAzureLinux
Baseline | [ca073c0866e1504313b43781c209f7f680d0ecb3](https://github.com/dotnet/runtime/commit/ca073c0866e1504313b43781c209f7f680d0ecb3)
Compare | [00115f085a2df36ea7b135673d290298e20775f7](https://github.com/dotnet/runtime/commit/00115f085a2df36ea7b135673d290298e20775f7)
Diff | [Diff](https://github.com/dotnet/runtime/compare/ca073c0866e1504313b43781c209f7f680d0ecb3...00115f085a2df36ea7b135673d290298e20775f7)
Configs | CompilationMode:tiered, R2RType:r2r_interpreter, RunKind:micro

### Regressions in System.IO.Tests.StreamReaderReadLineTests

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

• [ReadLine - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config 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
py .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.IO.Tests.StreamReaderReadLineTests*'
```

### System.IO.Tests.StreamReaderReadLineTests.ReadLine(LineLengthRange: [ 1, 1])

#### 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 StreamReaderReadLineTests.cs benchmark and run the provided benchmarks_ci.py command using the System.IO.Tests.StreamReaderReadLineTests filter. Compare the baseline and test commits, then use the linked test report and profiling workflow to identify the cause of the 12% ARM64 regression. Done means the regression is explained and the benchmark no longer shows the slowdown.

Written by the indexing model from the issue text.