[Perf] Linux/x64: 2 Regressions on 8/25/2026 11:54:37 AM +00:00

### Run Information

Name | Value
-- | --
Architecture | x64
OS | ubuntu 22.04
Queue | ViperUbuntu
Baseline | [6d57017f1cbf04efa931389d38ca4755e4da8add](https://github.com/dotnet/runtime/commit/6d57017f1cbf04efa931389d38ca4755e4da8add)
Compare | [519e88bf80b5d39bc2c4e788a025a499136a1661](https://github.com/dotnet/runtime/commit/519e88bf80b5d39bc2c4e788a025a499136a1661)
Diff | [Diff](https://github.com/dotnet/runtime/compare/6d57017f1cbf04efa931389d38ca4755e4da8add...519e88bf80b5d39bc2c4e788a025a499136a1661)
Configs | CompilationMode:wasm, RunKind:micro

### Regressions in System.Perf_Convert

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

• [FromBase64Chars - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 245.83 ns | 281.20 ns | 1.14 | 0.15 | False | | |
|

• [FromBase64String - Duration of single invocation]()
• 📝 - [Benchmark Source]()
• [ADX - Test Multi Config Graph]()

| 245.43 ns | 267.89 ns | 1.09 | 0.19 | False | | |

![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.Perf_Convert*'
```

### System.Perf_Convert.FromBase64Chars

#### ETL Files

#### Histogram

#### JIT Disasms

### System.Perf_Convert.FromBase64String

#### 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.Runtime.Extensions/Perf.Convert.cs at lines 77-84 and reproduce System.Perf_Convert with the documented benchmarks_ci.py command. Compare the baseline and test commits, then inspect the linked performance reports for FromBase64String and FromBase64Chars. Done means the regression is explained and the affected benchmark performance is restored or the result is otherwise validated.

Written by the indexing model from the issue text.