[Perf] Linux/arm64: 1 Regression on 6/30/2026 1:37:08 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | azurelinux 3.0
Queue | CobaltAzureLinux
Baseline | [b6f8d204bdbbf2c00f38aaf0f7f84abd9078341f](https://github.com/dotnet/runtime/commit/b6f8d204bdbbf2c00f38aaf0f7f84abd9078341f)
Compare | [5b16e5d49ce3be98845c4253219bd94458415953](https://github.com/dotnet/runtime/commit/5b16e5d49ce3be98845c4253219bd94458415953)
Diff | [Diff](https://github.com/dotnet/runtime/compare/b6f8d204bdbbf2c00f38aaf0f7f84abd9078341f...5b16e5d49ce3be98845c4253219bd94458415953)
Configs | CompilationMode:tiered, R2RType:r2r_interpreter, RunKind:micro

### Regressions in System.Diagnostics.Perf_Activity

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

• [EnumerateActivityTagsSmall - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config 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.Diagnostics.Perf_Activity*'
```

### System.Diagnostics.Perf_Activity.EnumerateActivityTagsSmall

#### 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 System.Diagnostics/Perf_Activity benchmark source at src/benchmarks/micro/libraries/System.Diagnostics/Perf_Activity.cs#L105-L111 and compare the listed baseline and test commits. Run the provided benchmarks_ci.py command, then inspect the linked test report and history for EnumerateActivityTagsSmall. Done means reproducing the regression and establishing its cause and resolution.

Written by the indexing model from the issue text.