[Perf] Windows/x86: 87 Regressions on 1/23/2026 10:32:11 PM +00:00

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#67,961 opened on Jan 27, 2026 4 comments 0 reactions 0 assignees View on GitHub

arch-x86 branch-refs/heads/main kind-micro os-windows perf-regression 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 | [f7cbeb10f3b900ca4de0eb719a85ae206e3472e9](https://github.com/dotnet/runtime/commit/f7cbeb10f3b900ca4de0eb719a85ae206e3472e9)
Compare | [9baed28a0526f4c164ba1043edeeb8718df7aabb](https://github.com/dotnet/runtime/commit/9baed28a0526f4c164ba1043edeeb8718df7aabb)
Diff | [Diff](https://github.com/dotnet/runtime/compare/f7cbeb10f3b900ca4de0eb719a85ae206e3472e9...9baed28a0526f4c164ba1043edeeb8718df7aabb)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Memory.ReadOnlySequence

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

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

| 24.08 ns | 25.61 ns | 1.06 | 0.00 | False | | |
|

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

| 8.12 ns | 9.44 ns | 1.16 | 0.25 | False | | |

[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.ReadOnlySequence*'
```

### System.Memory.ReadOnlySequence.Slice_Repeat(Segment: Multiple)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Memory.ReadOnlySequence.Slice_Start_And_Length(Segment: Multiple)

#### 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.Text.Tests.Perf_Encoding

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

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

| 15.25 ns | 16.66 ns | 1.09 | 0.36 | False | | |
|

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

| 13.14 ns | 14.33 ns | 1.09 | 0.36 | False | | |
|

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

| 15.84 ns | 16.85 ns | 1.06 | 0.40 | False | | |
|

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

| 5.18 ns | 7.82 ns | 1.51 | 0.06 | False | | |
|

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

| 9.65 ns | 11.31 ns | 1.17 | 0.07 | False | | |

[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.Tests.Perf_Encoding*'
```

### System.Text.Tests.Perf_Encoding.GetBytes(size: 16, encName: "utf-8")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Tests.Perf_Encoding.GetByteCount(size: 512, encName: "utf-8")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Tests.Perf_Encoding.GetChars(size: 16, encName: "utf-8")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Tests.Perf_Encoding.GetByteCount(size: 16, encName: "utf-8")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Tests.Perf_Encoding.GetString(size: 16, encName: "ascii")

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Text.Perf_Ascii

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

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

| 13.51 ns | 15.15 ns | 1.12 | 0.11 | False | | |
|

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

| 10.53 ns | 13.70 ns | 1.30 | 0.51 | False | | |

[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.Perf_Ascii*'
```

### System.Text.Perf_Ascii.ToLower_Bytes_Chars(Size: 6)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Perf_Ascii.ToUpper_Chars(Size: 128)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Tests.Perf_Random

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

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

| 1.16 ns | 2.90 ns | 2.50 | 0.62 | False | | |
|

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

| 2.56 ns | 4.19 ns | 1.64 | 0.17 | False | | |

[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_Random*'
```

### System.Tests.Perf_Random.NextDouble

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_Random.Next_long_unseeded

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Tests.Perf_String

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

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

| 23.26 ns | 25.31 ns | 1.09 | 0.05 | False | | |
|

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

| 4.08 ns | 5.09 ns | 1.25 | 0.10 | False | | |
|

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

| 150.52 ns | 166.97 ns | 1.11 | 0.04 | False | | |
|

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

| 8.56 ns | 9.86 ns | 1.15 | 0.07 | False | | |
|

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

| 11.80 ns | 13.89 ns | 1.18 | 0.25 | False | | |
|

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

| 20.21 ns | 22.26 ns | 1.10 | 0.21 | False | | |

[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.Replace_String(text: "This is a very nice sentence. This is another very nice sentence.", oldValue: "a", newValue: "b")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.PadLeft(n: 18)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.Join_Enumerable

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.Replace_String(text: "This is a very nice sentence", oldValue: "bad", newValue: "nice")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.ToUpperInvariant(s: "TeSt")

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Tests.Perf_String.ToUpper(s: "This is a much longer piece of text that might benefit more from vectorization.")

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Threading.Tests.Perf_Volatile

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

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

| 11.73 ns | 13.52 ns | 1.15 | 0.28 | False | | |

[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.Threading.Tests.Perf_Volatile*'
```

### System.Threading.Tests.Perf_Volatile.Read_double

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Numerics.Tests.Perf_BigInteger

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

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

| 5.21 ns | 6.68 ns | 1.28 | 0.25 | False | | |
|

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

| 18.63 ns | 20.00 ns | 1.07 | 0.01 | False | | |

[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.Numerics.Tests.Perf_BigInteger*'
```

### System.Numerics.Tests.Perf_BigInteger.ToByteArray(numberString: 123)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Numerics.Tests.Perf_BigInteger.GreatestCommonDivisor(arguments: 16,16 bits)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

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

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

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

| 12.08 μs | 15.19 μs | 1.26 | 0.01 | False | | |

[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.CreateAddAndClear*'
```

### System.Collections.CreateAddAndClear<String>.IDictionary(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Collections.TryGetValueFalse<BigStruct, BigStruct>

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

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

| 37.27 μs | 43.55 μs | 1.17 | 0.12 | False | | |

[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.TryGetValueFalse*'
```

### System.Collections.TryGetValueFalse<BigStruct, BigStruct>.SortedDictionary(Size: 512)

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Reflection.Invoke

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

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

| 9.12 ns | 10.79 ns | 1.18 | 0.09 | False | | |
|

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

| 9.71 ns | 11.71 ns | 1.21 | 0.05 | False | | |
|

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

| 9.00 ns | 11.21 ns | 1.25 | 0.05 | False | | |
|

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

| 8.73 ns | 9.92 ns | 1.14 | 0.04 | False | | |
|

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

| 11.10 ns | 13.58 ns | 1.22 | 0.23 | False | | |

[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.Invoke*'
```

### System.Reflection.Invoke.Field_Get_int

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Reflection.Invoke.Field_Get_struct

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Reflection.Invoke.Field_GetStatic_struct

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Reflection.Invoke.Field_GetStatic_int

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Reflection.Invoke.Property_Set_class

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

---

### Run Information

### Regressions in System.Tests.Perf_DateTimeOffset

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

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

| 36.36 ns | 38.33 ns | 1.05 | 0.06 | False | | |

[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_DateTimeOffset*'
```

### System.Tests.Perf_DateTimeOffset.GetUtcNow

#### ETL Files

#### Histogram

#### JIT Disasms

### Docs

Contributor guide

No contributing guide indexed for this repository

Research direction

Start with docs/benchmarking-workflow-dotnet-runtime.md and the reported benchmark sources src/benchmarks/micro/libraries/System.Memory/ReadOnlySequence.cs and src/benchmarks/micro/libraries/System.Text.Encoding/Perf.Encoding.cs. Run the provided benchmarks_ci.py command on Windows/x86, then compare the results with the linked baseline and test reports. Done means the regressions are explained and an appropriate follow-up or fix is identified.

Written by the indexing model from the issue text.

Assessment

Tech stack: csharp
Domain: performance
Issue type: Bug
Difficulty: 4/5
Estimated time: 3-5 days
Activity status: Stale
Clarity: Needs clarification
Newbie friendliness: 35/100

[Perf] Windows/x86: 87 Regressions on 1/23/2026 10:32:11 PM +00:00

Description

Contributor guide

Research direction

Assessment

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