[Perf] Linux/arm64: 3 Regressions on 8/4/2026 6:24:26 PM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | ubuntu 22.04
Queue | AmpereUbuntu
Baseline | [854ee0872ab804701b45b64fdf794944657d4bc8](https://github.com/dotnet/runtime/commit/854ee0872ab804701b45b64fdf794944657d4bc8)
Compare | [173e6b40e02cd1652102c09e07bd4cf7320b3d4d](https://github.com/dotnet/runtime/commit/173e6b40e02cd1652102c09e07bd4cf7320b3d4d)
Diff | [Diff](https://github.com/dotnet/runtime/compare/854ee0872ab804701b45b64fdf794944657d4bc8...173e6b40e02cd1652102c09e07bd4cf7320b3d4d)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in System.Text.Perf_Utf8Encoding

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

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

| 46.89 μs | 59.27 μs | 1.26 | 0.39 | False | | |
|

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

| 234.59 μs | 257.68 μs | 1.10 | 0.13 | False | | |
|

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

| 280.22 μs | 303.86 μs | 1.08 | 0.02 | False | | |

![graph]()
![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
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.Perf_Utf8Encoding*'
```

### System.Text.Perf_Utf8Encoding.GetCharCount(Input: EnglishMostlyAscii)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Perf_Utf8Encoding.GetBytesFromString(Input: Greek)

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Text.Perf_Utf8Encoding.GetStringFromBytes(Input: EnglishMostlyAscii)

#### 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 source at performance/src/benchmarks/micro/libraries/System.Text.Encoding/Perf.Utf8Encoding.cs and reproduce the three cases using the provided benchmarks_ci.py command. Compare the baseline and test commits, then use the linked performance and profiling reports to identify the regression. Done means the arm64 benchmark results no longer show these regressions.

Written by the indexing model from the issue text.