[Perf] Linux/x64: 1 Regression on 9/1/2026 5:28:08 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [ef3efe5e020e412e4f6453781d59443e975010a4](https://github.com/dotnet/runtime/commit/ef3efe5e020e412e4f6453781d59443e975010a4)
Compare | [818ad35699cf9b1a3e3f2067c133d8dbe599da2e](https://github.com/dotnet/runtime/commit/818ad35699cf9b1a3e3f2067c133d8dbe599da2e)
Diff | [Diff](https://github.com/dotnet/runtime/compare/ef3efe5e020e412e4f6453781d59443e975010a4...818ad35699cf9b1a3e3f2067c133d8dbe599da2e)
Configs | CompilationMode:wasm, RunKind:micro

### Regressions in System.IO.Tests.Perf_File

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

• [WriteAllBytes - 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_File*'
```

### System.IO.Tests.Perf_File.WriteAllBytes(size: 1048576)

#### 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.File.cs around lines 84-90 and reproduce System.IO.Tests.Perf_File.WriteAllBytes using the provided benchmarks_ci.py command. Compare the baseline and test commits and use the linked performance report to investigate the regression. Done means the cause is identified and the benchmark no longer shows the regression.

Written by the indexing model from the issue text.