[Perf] Linux/x64: 1 Regression on 8/10/2026 5:40:28 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [9904b9343c89c898fea3a9dfa68a6aba7fa8f3c1](https://github.com/dotnet/runtime/commit/9904b9343c89c898fea3a9dfa68a6aba7fa8f3c1)
Compare | [ab094c18ba7f4a96d145afd8b34f965c5c3ef31d](https://github.com/dotnet/runtime/commit/ab094c18ba7f4a96d145afd8b34f965c5c3ef31d)
Diff | [Diff](https://github.com/dotnet/runtime/compare/9904b9343c89c898fea3a9dfa68a6aba7fa8f3c1...ab094c18ba7f4a96d145afd8b34f965c5c3ef31d)
Configs | AOT:true, CompilationMode:wasm, RunKind:micro

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

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

• [Read_NoBuffering - 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
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.IO.Tests.Perf_FileStream*'
```

### System.IO.Tests.Perf_FileStream.Read_NoBuffering(fileSize: 104857600, userBufferSize: 16384, 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 src/benchmarks/micro/libraries/System.IO.FileSystem/Perf.FileStream.cs at lines 204-207 and compare the baseline and test commits. Run the provided benchmarks_ci.py command with the System.IO.Tests.Perf_FileStream filter, then use the linked report and profiling workflow to investigate the Read_NoBuffering regression. Done means identifying and addressing the cause, with the benchmark no longer showing the reported slowdown.

Written by the indexing model from the issue text.