[Perf] Linux/x64: 2 Regressions on 8/14/2026 7:15:06 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [691fd960eb500743b4be71373b11b2263bdbc318](https://github.com/dotnet/runtime/commit/691fd960eb500743b4be71373b11b2263bdbc318)
Compare | [c99188c2f97b94c8b086cc9b87516b6d710ec4ff](https://github.com/dotnet/runtime/commit/c99188c2f97b94c8b086cc9b87516b6d710ec4ff)
Diff | [Diff](https://github.com/dotnet/runtime/compare/691fd960eb500743b4be71373b11b2263bdbc318...c99188c2f97b94c8b086cc9b87516b6d710ec4ff)
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
-- | -- | -- | -- | -- | -- | -- | -- | --
|

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

| 865.87 μs | 1730.68 μs | 2.00 | 0.31 | 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>.ImmutableList(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 | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [691fd960eb500743b4be71373b11b2263bdbc318](https://github.com/dotnet/runtime/commit/691fd960eb500743b4be71373b11b2263bdbc318)
Compare | [c99188c2f97b94c8b086cc9b87516b6d710ec4ff](https://github.com/dotnet/runtime/commit/c99188c2f97b94c8b086cc9b87516b6d710ec4ff)
Diff | [Diff](https://github.com/dotnet/runtime/compare/691fd960eb500743b4be71373b11b2263bdbc318...c99188c2f97b94c8b086cc9b87516b6d710ec4ff)
Configs | CompilationMode:wasm, RunKind:micro, RuntimeType:coreclr

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

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

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

| 2.45 μs | 3.52 μs | 1.43 | 0.28 | 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.Buffers.Tests.ReadOnlySequenceTests*'
```

### System.Buffers.Tests.ReadOnlySequenceTests<Char>.IterateForEachMemory

#### 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.Collections/Create/CtorFromCollection.cs#L93-L94 and src/benchmarks/micro/libraries/System.Buffers/ReadOnlySequenceTests.cs#L95-L96. Run benchmarks_ci.py with the two filters from the issue, then compare the reported runs with the linked baseline and test reports. Done means both regressions are reproduced and their performance impact is explained or resolved.

Written by the indexing model from the issue text.