[Perf] Linux/x64: 2 Regressions on 8/3/2026 7:26:34 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [79efd2de59f086171fd811d7375241616c43b890](https://github.com/dotnet/runtime/commit/79efd2de59f086171fd811d7375241616c43b890)
Compare | [c4fc2a5afc5644e10973054b1aa63c27a1584404](https://github.com/dotnet/runtime/commit/c4fc2a5afc5644e10973054b1aa63c27a1584404)
Diff | [Diff](https://github.com/dotnet/runtime/compare/79efd2de59f086171fd811d7375241616c43b890...c4fc2a5afc5644e10973054b1aa63c27a1584404)
Configs | AOT:true, CompilationMode:wasm, RunKind:micro

### Regressions in System.Text.Tests.Perf_StringBuilder

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

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

| 51.64 ns | 57.57 ns | 1.11 | 0.10 | 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
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.Tests.Perf_StringBuilder*'
```

### System.Text.Tests.Perf_StringBuilder.ToString_SingleSegment(length: 100)

#### 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 | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [79efd2de59f086171fd811d7375241616c43b890](https://github.com/dotnet/runtime/commit/79efd2de59f086171fd811d7375241616c43b890)
Compare | [c4fc2a5afc5644e10973054b1aa63c27a1584404](https://github.com/dotnet/runtime/commit/c4fc2a5afc5644e10973054b1aa63c27a1584404)
Diff | [Diff](https://github.com/dotnet/runtime/compare/79efd2de59f086171fd811d7375241616c43b890...c4fc2a5afc5644e10973054b1aa63c27a1584404)
Configs | AOT:true, CompilationMode:wasm, RunKind:micro

### Regressions in System.Tests.Perf_Enum

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

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

| 77.96 ns | 91.67 ns | 1.18 | 0.13 | 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
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Tests.Perf_Enum*'
```

### System.Tests.Perf_Enum.ToString_Format_NonFlags(value: Wednesday, format: "x")

#### 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 at src/benchmarks/micro/libraries/System.Text/Perf.StringBuilder.cs and src/benchmarks/micro/libraries/System.Runtime/Perf.Enum.cs. Run the two benchmarks with the documented benchmarks_ci.py commands, then compare the baseline and test commits and use the profiling workflow if the regressions reproduce. Done means the regression is explained and the affected benchmark no longer shows the reported slowdown.

Written by the indexing model from the issue text.