[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 the System.IO.Tests.Perf_File.WriteAllBytes benchmark and its source in performance/src/benchmarks/micro/libraries/System.IO.FileSystem/Perf.File.cs#L84-L90. Reproduce it with the listed benchmarks_ci.py command, then compare the baseline and test commits and review the linked performance and profiling workflows. Done means the regression is explained and the benchmark result is validated against the reported baseline.

Written by the indexing model from the issue text.