[Perf] Windows/x86: 40 Regressions on 9/11/2026 9:48:28 PM +00:00

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#79,390 opened on Sep 15, 2026 2 comments 0 reactions 0 assignees View on GitHub

arch-x86 branch-refs/heads/main compilationmode-tiered kind-micro Look Again os-windows perf-regression PGO runkind-micro runtime-coreclr untriaged

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Forks: 8
PR merge metrics: PR metrics pending

Description

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [de29e26a4f69da5d446900a6ba9d68ba3ddc5ba9](https://github.com/dotnet/runtime/commit/de29e26a4f69da5d446900a6ba9d68ba3ddc5ba9)
Compare | [0fd08c887c1317055025965cbe829b732fbe942d](https://github.com/dotnet/runtime/commit/0fd08c887c1317055025965cbe829b732fbe942d)
Diff | [Diff](https://github.com/dotnet/runtime/compare/de29e26a4f69da5d446900a6ba9d68ba3ddc5ba9...0fd08c887c1317055025965cbe829b732fbe942d)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Tests.Perf_GC<Byte>

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

[AllocateUninitializedArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 144.62 ns | 195.09 ns | 1.35 | 0.03 | False | | |
|

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

| 259.30 ns | 342.17 ns | 1.32 | 0.04 | False | | |
|

[AllocateUninitializedArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 1.67 μs | 2.09 μs | 1.25 | 0.32 | False | | |
|

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

| 30.86 ns | 36.39 ns | 1.18 | 0.04 | False | | |
|

[AllocateUninitializedArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 31.36 ns | 36.72 ns | 1.17 | 0.04 | False | | |
|

[AllocateArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 1.86 μs | 2.10 μs | 1.13 | 0.30 | False | | |

![graph]()
![graph]()
![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.Tests.Perf_GC*'
```

### System.Tests.Perf_GC<Byte>.AllocateUninitializedArray(length: 10000, pinned: False)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Byte>.NewOperator_Array(length: 10000)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Byte>.AllocateUninitializedArray(length: 10000, pinned: True)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Byte>.NewOperator_Array(length: 1000)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Byte>.AllocateUninitializedArray(length: 1000, pinned: False)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Byte>.AllocateArray(length: 10000, pinned: True)

#### 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

### Regressions in System.Tests.Perf_String

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

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

| 14.76 ns | 16.83 ns | 1.14 | 0.04 | False | | |
|

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

| 161.82 ns | 182.71 ns | 1.13 | 0.02 | False | | |
|

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

| 50.84 ns | 54.80 ns | 1.08 | 0.04 | False | | |
|

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

| 39.23 ns | 42.05 ns | 1.07 | 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.Tests.Perf_String*'
```

### System.Tests.Perf_String.GetChars(size: 100)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.PadLeft(n: 2142)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.Concat_str_str_str_str(size: 100)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.Concat_str_str_str(size: 100)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Tests.Perf_GC<Char>

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

[AllocateUninitializedArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 206.73 ns | 307.87 ns | 1.49 | 0.05 | False | | |
|

[AllocateUninitializedArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 2.20 μs | 2.85 μs | 1.30 | 0.19 | False | | |
|

[AllocateArray - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 439.18 ns | 541.23 ns | 1.23 | 0.02 | False | | |
|

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

| 58.82 ns | 68.81 ns | 1.17 | 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.Tests.Perf_GC*'
```

### System.Tests.Perf_GC<Char>.AllocateUninitializedArray(length: 10000, pinned: False)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Char>.AllocateUninitializedArray(length: 10000, pinned: True)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Char>.AllocateArray(length: 10000, pinned: False)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_GC<Char>.NewOperator_Array(length: 1000)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Tests.Perf_Array

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

[ArrayCreate1D - Duration of single invocation]()
📝 - [Benchmark Source]()
[ADX - Test Multi Config Graph]()

| 380.49 ns | 469.61 ns | 1.23 | 0.02 | False | | |
|

[ArrayCreate2D - Duration of single invocation]()
📝 - [Benchmark Source]()
[ADX - Test Multi Config Graph]()

| 432.85 ns | 515.88 ns | 1.19 | 0.02 | False | | |
|

[ArrayCreate3D - Duration of single invocation]()
📝 - [Benchmark Source]()
[ADX - Test Multi Config Graph]()

| 448.75 ns | 525.10 ns | 1.17 | 0.02 | False | | |

![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.Tests.Perf_Array*'
```

### System.Tests.Perf_Array.ArrayCreate1D

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_Array.ArrayCreate2D

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_Array.ArrayCreate3D

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Buffers.Tests.ReadOnlySequenceTests<Byte>

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

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

| 23.57 ns | 35.18 ns | 1.49 | 0.03 | False | | |
|

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

| 54.93 ns | 60.80 ns | 1.11 | 0.03 | 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.Buffers.Tests.ReadOnlySequenceTests*'
```

### System.Buffers.Tests.ReadOnlySequenceTests<Byte>.IterateForEachTenSegments

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Buffers.Tests.ReadOnlySequenceTests<Byte>.IterateGetPositionTenSegments

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Collections.CtorGivenSize<Int32>

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

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

| 60.24 ns | 71.33 ns | 1.18 | 0.03 | 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.Collections.CtorGivenSize*'
```

### System.Collections.CtorGivenSize<Int32>.Array(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Collections.IterateForEach<String>

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

[OrderedDictionary - Duration of single invocation]()
[ADX - Test Multi Config Graph]()

| 2.21 μs | 2.49 μs | 1.12 | 0.27 | 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.Collections.IterateForEach*'
```

### System.Collections.IterateForEach<String>.OrderedDictionary(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in ByteMark

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

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

| 652.67 ms | 1094.29 ms | 1.68 | 0.14 | 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 'ByteMark*'
```

### ByteMark.BenchBitOps

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Mariomkas

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

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

| 600.44 μs | 655.25 μs | 1.09 | 0.01 | 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.Text.RegularExpressions.Tests.Perf_Regex_Industry_Mariomkas*'
```

### System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Mariomkas.Ctor(Pattern: "[\\w\\.+-]+@[\\w\\.-]+\\.[\\w\\.-]+", Options: NonBacktracking)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Memory.Span<Char>

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

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

| 17.98 ns | 20.05 ns | 1.12 | 0.29 | 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.Memory.Span*'
```

### System.Memory.Span<Char>.SequenceCompareTo(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Memory.Span<Byte>

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

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

| 133.09 ns | 148.13 ns | 1.11 | 0.04 | 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.Memory.Span*'
```

### System.Memory.Span<Byte>.ToArray(Size: 3000)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Reflection.Attributes

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

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

| 186.43 ns | 200.30 ns | 1.07 | 0.04 | 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.Reflection.Attributes*'
```

### System.Reflection.Attributes.GetCustomAttributesClassMissInherit

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

Name | Value
-- | --
Architecture | x86
OS | Windows 10.0.22631
Queue | ViperWindows
Baseline | [de29e26a4f69da5d446900a6ba9d68ba3ddc5ba9](https://github.com/dotnet/runtime/commit/de29e26a4f69da5d446900a6ba9d68ba3ddc5ba9)
Compare | [ea973e7517a629d0c3c75f4879ce279b07f21365](https://github.com/dotnet/runtime/commit/ea973e7517a629d0c3c75f4879ce279b07f21365)
Diff | [Diff](https://github.com/dotnet/runtime/compare/de29e26a4f69da5d446900a6ba9d68ba3ddc5ba9...ea973e7517a629d0c3c75f4879ce279b07f21365)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Collections.CtorFromCollection<Int32>

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

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

| 94.68 ns | 106.62 ns | 1.13 | 0.03 | 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.Collections.CtorFromCollection*'
```

### System.Collections.CtorFromCollection<Int32>.ImmutableArray(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

Contributor guide

No contributing guide indexed for this repository

Research direction

Start with the reported performance diff and the reproduction command in scripts/benchmarks_ci.py, then inspect the benchmark source at src/benchmarks/micro/runtime/GC/Perf_GC.cs. Compare the baseline and test commits and use the referenced test report to determine whether the Windows/x86 regressions reproduce. Done means identifying and correcting the regression, with the affected benchmarks no longer regressing.

Written by the indexing model from the issue text.

Assessment

Tech stack: git, python
Domain: performance, testing, tooling
Issue type: Bug
Difficulty: 4/5
Estimated time: 3-5 days
Activity status: Active
Clarity: Needs clarification
Newbie friendliness: 30/100

[Perf] Windows/x86: 40 Regressions on 9/11/2026 9:48:28 PM +00:00

Description

Contributor guide

Research direction

Assessment

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