[Perf] Linux/arm64: 5 Regressions on 6/29/2026 9:51:56 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | arm64
OS | azurelinux 3.0
Queue | CobaltAzureLinux
Baseline | [0d3df07c6048d8cbe4f544227462cae62040e587](https://github.com/dotnet/runtime/commit/0d3df07c6048d8cbe4f544227462cae62040e587)
Compare | [93ec56ee6c38a470c6fed16b59d3f130587b1a06](https://github.com/dotnet/runtime/commit/93ec56ee6c38a470c6fed16b59d3f130587b1a06)
Diff | [Diff](https://github.com/dotnet/runtime/compare/0d3df07c6048d8cbe4f544227462cae62040e587...93ec56ee6c38a470c6fed16b59d3f130587b1a06)
Configs | CompilationMode:tiered, R2RType:r2r_interpreter, RunKind:micro

### Regressions in System.Formats.Tar.Tests.Perf_TarWriter

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

• [V7TarEntry_WriteEntry - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 561.20 ns | 1199.22 ns | 2.14 | 0.10 | False | | |
|

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

| 616.08 ns | 1243.17 ns | 2.02 | 0.09 | False | | |
|

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

| 603.40 ns | 1205.69 ns | 2.00 | 0.07 | False | | |
|

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

| 6.58 μs | 8.17 μs | 1.24 | 0.12 | False | | |

![graph]()
![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
py .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Formats.Tar.Tests.Perf_TarWriter*'
```

### System.Formats.Tar.Tests.Perf_TarWriter.V7TarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.GnuTarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.UstarTarEntry_WriteEntry

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Formats.Tar.Tests.Perf_TarWriter.PaxTarEntry_WriteEntry

#### 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 | [0d3df07c6048d8cbe4f544227462cae62040e587](https://github.com/dotnet/runtime/commit/0d3df07c6048d8cbe4f544227462cae62040e587)
Compare | [93ec56ee6c38a470c6fed16b59d3f130587b1a06](https://github.com/dotnet/runtime/commit/93ec56ee6c38a470c6fed16b59d3f130587b1a06)
Diff | [Diff](https://github.com/dotnet/runtime/compare/0d3df07c6048d8cbe4f544227462cae62040e587...93ec56ee6c38a470c6fed16b59d3f130587b1a06)
Configs | CompilationMode:tiered, R2RType:r2r_interpreter, RunKind:micro

### Regressions in System.Collections.Concurrent.IsEmpty<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]()

| 135.68 ns | 157.51 ns | 1.16 | 0.37 | 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.Collections.Concurrent.IsEmpty*'
```

### System.Collections.Concurrent.IsEmpty<String>.Dictionary(Size: 0)

#### 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 linked benchmark sources in performance/src/benchmarks/micro/libraries/System.Formats.Tar/Perf.Tar.cs and System.Collections/Concurrent/IsEmpty.cs. Run the provided benchmarks and compare the baseline and compare commits, then inspect the linked test reports and graphs. Done means the reported ARM64 regressions have an identified cause and an agreed corrective change or disposition.

Written by the indexing model from the issue text.