[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
-- | -- | -- | -- | -- | -- | -- | -- | --
|

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

| 292.78 ns | 378.64 ns | 1.29 | 0.08 | False | | |
|

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

| 315.75 ns | 392.91 ns | 1.24 | 0.06 | False | | |
|

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

| 1.80 μs | 2.19 μs | 1.22 | 0.01 | False | | |
|

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

| 291.98 ns | 356.40 ns | 1.22 | 0.03 | 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.UstarTarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.GnuTarEntry_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.V7TarEntry_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 benchmark entry points in performance/src/benchmarks/micro/libraries/System.Formats.Tar/Perf.Tar.cs at lines 45-51, 61-67, 77-83, and 93-99. Run the provided benchmarks_ci.py command, then compare the Windows/x86 results and reports against the listed baseline and comparison commits. Done means identifying and resolving the cause of the four TarWriter regressions, with the affected benchmarks no longer regressed.

Written by the indexing model from the issue text.