[Perf] Windows/x86: 4 Regressions on 6/29/2026 9:51:56 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [0d3df07c6048d8cbe4f544227462cae62040e587](https://github.com/dotnet/runtime/commit/0d3df07c6048d8cbe4f544227462cae62040e587)
Compare | [93ec56ee6c38a470c6fed16b59d3f130587b1a06](https://github.com/dotnet/runtime/commit/93ec56ee6c38a470c6fed16b59d3f130587b1a06)
Diff | [Diff](https://github.com/dotnet/runtime/compare/0d3df07c6048d8cbe4f544227462cae62040e587...93ec56ee6c38a470c6fed16b59d3f130587b1a06)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Formats.Tar.Tests.Perf_TarWriter

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

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

| 309.16 ns | 382.63 ns | 1.24 | 0.07 | False | | |
|

• [V7TarEntry_WriteEntry - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 289.25 ns | 351.81 ns | 1.22 | 0.04 | False | | |
|

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

| 1.81 μs | 2.19 μs | 1.21 | 0.01 | False | | |
|

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

| 308.56 ns | 364.01 ns | 1.18 | 0.08 | False | | |

![graph]()
![graph]()
![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.Formats.Tar.Tests.Perf_TarWriter*'
```

### System.Formats.Tar.Tests.Perf_TarWriter.GnuTarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.V7TarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.PaxTarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.UstarTarEntry_WriteEntry

#### 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 four Perf_TarWriter benchmarks in performance/src/benchmarks/micro/libraries/System.Formats.Tar/Perf.Tar.cs and compare the listed baseline and compare commits. Run the provided benchmarks_ci.py command, then use the linked test report and regression graphs to investigate the x86 Windows slowdown. Done means the regressions are explained and addressed or appropriately triaged.

Written by the indexing model from the issue text.