[Perf] Windows/x86: 3 Regressions on 8/5/2026 6:23:30 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [f107b2325cccfd453f9bf46013159f4704ea56c2](https://github.com/dotnet/runtime/commit/f107b2325cccfd453f9bf46013159f4704ea56c2)
Compare | [b6caa7d9ec9b346b2b09a31ab3fccfe7d049b723](https://github.com/dotnet/runtime/commit/b6caa7d9ec9b346b2b09a31ab3fccfe7d049b723)
Diff | [Diff](https://github.com/dotnet/runtime/compare/f107b2325cccfd453f9bf46013159f4704ea56c2...b6caa7d9ec9b346b2b09a31ab3fccfe7d049b723)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Collections.Tests.Perf_BitArray

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

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

| 9.58 ns | 11.01 ns | 1.15 | 0.08 | False | | |
|

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

| 12.16 ns | 13.82 ns | 1.14 | 0.05 | False | | |

![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.Collections.Tests.Perf_BitArray*'
```

### System.Collections.Tests.Perf_BitArray.BitArrayBitArrayCtor(Size: 4)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Collections.Tests.Perf_BitArray.BitArrayBitArrayCtor(Size: 512)

#### 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)

---

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [f107b2325cccfd453f9bf46013159f4704ea56c2](https://github.com/dotnet/runtime/commit/f107b2325cccfd453f9bf46013159f4704ea56c2)
Compare | [b6caa7d9ec9b346b2b09a31ab3fccfe7d049b723](https://github.com/dotnet/runtime/commit/b6caa7d9ec9b346b2b09a31ab3fccfe7d049b723)
Diff | [Diff](https://github.com/dotnet/runtime/compare/f107b2325cccfd453f9bf46013159f4704ea56c2...b6caa7d9ec9b346b2b09a31ab3fccfe7d049b723)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Diagnostics.Tracing.Perf_EventListener

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

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

| 58.36 ns | 64.46 ns | 1.10 | 0.06 | False | | |

![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.Diagnostics.Tracing.Perf_EventListener*'
```

### System.Diagnostics.Tracing.Perf_EventListener.WriteEvent_NoParams

#### 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 sources src/benchmarks/micro/libraries/System.Collections/Perf.BitArray.cs and src/benchmarks/micro/libraries/System.Diagnostics.Tracing/Perf_EventListener.cs, then review the baseline and compare commits in the issue. Run the provided benchmarks_ci.py commands using the benchmarking workflow documentation. Done means the reported x86 Windows regressions are explained and the affected benchmark results no longer regress.

Written by the indexing model from the issue text.