[Perf] Linux/x64: 2 Regressions on 7/11/2026 3:58:53 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [2f3204f6e8df27046832bb56afa980a923deaf91](https://github.com/dotnet/runtime/commit/2f3204f6e8df27046832bb56afa980a923deaf91)
Compare | [7203f39e30948cfe8362455433c43c1a0405cba3](https://github.com/dotnet/runtime/commit/7203f39e30948cfe8362455433c43c1a0405cba3)
Diff | [Diff](https://github.com/dotnet/runtime/compare/2f3204f6e8df27046832bb56afa980a923deaf91...7203f39e30948cfe8362455433c43c1a0405cba3)
Configs | CompilationMode:wasm, RunKind:micro, RuntimeType:coreclr

### Regressions in System.Text.Json.Serialization.Tests.ColdStartSerialization<SimpleStructWithProperties>

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

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

| 105.99 μs | 136.52 μs | 1.29 | 0.08 | 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.Json.Serialization.Tests.ColdStartSerialization*'
```

### System.Text.Json.Serialization.Tests.ColdStartSerialization<SimpleStructWithProperties>.NewDefaultOptions

#### 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 | [2f3204f6e8df27046832bb56afa980a923deaf91](https://github.com/dotnet/runtime/commit/2f3204f6e8df27046832bb56afa980a923deaf91)
Compare | [7203f39e30948cfe8362455433c43c1a0405cba3](https://github.com/dotnet/runtime/commit/7203f39e30948cfe8362455433c43c1a0405cba3)
Diff | [Diff](https://github.com/dotnet/runtime/compare/2f3204f6e8df27046832bb56afa980a923deaf91...7203f39e30948cfe8362455433c43c1a0405cba3)
Configs | CompilationMode:wasm, RunKind:micro, RuntimeType:coreclr

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

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

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

| 79.41 μs | 88.65 μs | 1.12 | 0.40 | 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.Collections.CtorFromCollection*'
```

### System.Collections.CtorFromCollection<String>.Dictionary(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)

Start with the benchmark sources at src/benchmarks/micro/libraries/System.Text.Json/Serializer/ColdStartSerialization.cs#L40-L41 and src/benchmarks/micro/libraries/System.Collections/Create/CtorFromCollection.cs#L51-L52. Run the listed benchmarks_ci.py commands and compare the baseline and test commits, then inspect the linked reports and profiling workflow. Done means identifying and addressing the cause of both reported regressions, with the benchmark results no longer regressed.

Written by the indexing model from the issue text.