[Perf] Linux/arm64: 2 Regressions on 8/5/2026 1:23:13 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | azurelinux 3.0
Queue | CobaltAzureLinux
Baseline | [ac85c6849c56dcb47e036b2a729c1e99dc413bab](https://github.com/dotnet/runtime/commit/ac85c6849c56dcb47e036b2a729c1e99dc413bab)
Compare | [c8f97975ab0d8ff84aebf176829e17f7c7052f03](https://github.com/dotnet/runtime/commit/c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Diff | [Diff](https://github.com/dotnet/runtime/compare/ac85c6849c56dcb47e036b2a729c1e99dc413bab...c8f97975ab0d8ff84aebf176829e17f7c7052f03)
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
-- | -- | -- | -- | -- | -- | -- | -- | --
|

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

| 162.41 μs | 174.95 μs | 1.08 | 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
py .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.Perf_Utf8Encoding*'
```

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

#### 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 | arm64
OS | azurelinux 3.0
Queue | CobaltAzureLinux
Baseline | [ac85c6849c56dcb47e036b2a729c1e99dc413bab](https://github.com/dotnet/runtime/commit/ac85c6849c56dcb47e036b2a729c1e99dc413bab)
Compare | [c8f97975ab0d8ff84aebf176829e17f7c7052f03](https://github.com/dotnet/runtime/commit/c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Diff | [Diff](https://github.com/dotnet/runtime/compare/ac85c6849c56dcb47e036b2a729c1e99dc413bab...c8f97975ab0d8ff84aebf176829e17f7c7052f03)
Configs | CompilationMode:tiered, RunKind:micro

### Regressions in Benchstone.BenchF.FFT

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

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

| 247.64 ms | 277.12 ms | 1.12 | 0.12 | 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
py .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'Benchstone.BenchF.FFT*'
```

### Benchstone.BenchF.FFT.Test

#### 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 src/benchmarks/micro/libraries/System.Text.Encoding/Perf.Utf8Encoding.cs and src/benchmarks/micro/runtime/Benchstones/BenchF/FFT.cs, then run the provided benchmarks_ci.py commands for the named filters. Compare the ARM64 AzureLinux results with the linked baseline and investigate the supplied regression reports. Done means the regressions are explained and the affected benchmark performance is restored or an evidence-backed runtime issue is identified.

Written by the indexing model from the issue text.