[Perf] Linux/x64: 17 Regressions on 1/23/2026 10:32:11 PM +00:00

[performanceautofiler]

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Text.Json.Serialization.Tests.WriteJson<Hashtable>

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
SerializeObjectProperty - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	5.01 μs	5.52 μs	1.10	0.03	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.Json.Serialization.Tests.WriteJson<Hashtable>*'

Details

System.Text.Json.Serialization.Tests.WriteJson<Hashtable>.SerializeObjectProperty(Mode: Reflection)

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Globalization.Tests.StringEquality

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
Compare_Same_Upper - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	729.63 ns	1.18 μs	1.62	0.02	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Globalization.Tests.StringEquality*'

Details

System.Globalization.Tests.StringEquality.Compare_Same_Upper(Count: 1024, Options: (en-US, OrdinalIgnoreCase))

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.IO.Tests.BinaryReaderTests

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
ReadUInt16 - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	1.53 ns	2.66 ns	1.74	0.13	False
ReadDouble - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	1.49 ns	2.68 ns	1.79	0.06	False
ReadSingle - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	1.49 ns	2.68 ns	1.79	0.08	False
ReadUInt32 - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	1.53 ns	2.66 ns	1.74	0.10	False
ReadUInt64 - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	1.53 ns	2.68 ns	1.76	0.10	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.IO.Tests.BinaryReaderTests*'

Details

System.IO.Tests.BinaryReaderTests.ReadUInt16

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JIT Disasms

System.IO.Tests.BinaryReaderTests.ReadDouble

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Histogram

JIT Disasms

System.IO.Tests.BinaryReaderTests.ReadSingle

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Histogram

JIT Disasms

System.IO.Tests.BinaryReaderTests.ReadUInt32

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Histogram

JIT Disasms

System.IO.Tests.BinaryReaderTests.ReadUInt64

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Histogram

JIT Disasms

Docs

Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Text.Perf_Ascii

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
ToUpper_Chars - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	11.79 ns	13.92 ns	1.18	0.11	False
ToLower_Chars - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	11.78 ns	13.62 ns	1.16	0.09	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.Perf_Ascii*'

Details

System.Text.Perf_Ascii.ToUpper_Chars(Size: 128)

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System.Text.Perf_Ascii.ToLower_Chars(Size: 128)

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Docs

Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in Span.IndexerBench

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
CoveredIndex2 - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	564.08 ns	604.72 ns	1.07	0.01	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'Span.IndexerBench*'

Details

Span.IndexerBench.CoveredIndex2(length: 1024)

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
Count - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	46.57 ms	49.83 ms	1.07	0.01	False
Count - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	46.52 ms	49.83 ms	1.07	0.02	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig*'

Details

System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count(Pattern: ".{0,2}(Tom|Sawyer|Huckleberry|Finn)", Options: NonBacktracking)

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System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count(Pattern: ".{2,4}(Tom|Sawyer|Huckleberry|Finn)", Options: NonBacktracking)

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in PerfLabTests.GetMember

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
GetMethod2 - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	70.37 μs	81.33 μs	1.16	0.07	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'PerfLabTests.GetMember*'

Details

PerfLabTests.GetMember.GetMethod2

ETL Files

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Collections.Tests.Perf_BitArray

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
BitArrayCopyToIntArray - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	4.31 ns	5.34 ns	1.24	0.05	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Collections.Tests.Perf_BitArray*'

Details

System.Collections.Tests.Perf_BitArray.BitArrayCopyToIntArray(Size: 4)

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Tests.Perf_Int64

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
TryParse - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	16.48 ns	19.39 ns	1.18	0.42	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Tests.Perf_Int64*'

Details

System.Tests.Perf_Int64.TryParse(value: "-9223372036854775808")

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in PerfLabTests.BlockCopyPerf

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
CallBlockCopy - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	13.96 ns	15.95 ns	1.14	0.34	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'PerfLabTests.BlockCopyPerf*'

Details

PerfLabTests.BlockCopyPerf.CallBlockCopy(numElements: 1000)

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Docs

Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

---

Run Information

Name	Value
Architecture	x64
OS	ubuntu 22.04
Queue	ViperUbuntu
Baseline	b1d2e4aa8af89cfa795015e30ef70d24ec92f67f
Compare	9baed28a0526f4c164ba1043edeeb8718df7aabb
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.IO.Tests.BinaryWriterTests

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
WriteHalf - Duration of single invocation ADX - Test Multi Config Graph	4.36 ns	5.39 ns	1.24	0.04	False

Test Report

Repro

General Docs link: https://github.com/dotnet/performance/blob/main/docs/benchmarking-workflow-dotnet-runtime.md

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.IO.Tests.BinaryWriterTests*'

Details

System.IO.Tests.BinaryWriterTests.WriteHalf

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Histogram

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Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

[LoopedBard3]

🔍 Automated Triage Analysis

Summary: 15 of 17 tests show confirmed regressions with high confidence. Most severe: BinaryReader methods regressed ~75-79% (z>28). GetMember.GetMethod2 +15.58% (z=39.33) likely caused by commit 0de4dab (FindMethod changes). BitArray +23.69% (z=51.35). One test is actually a major improvement (-99.84%), not a regression. Large commit range (74 commits) requires bisection for BinaryReader attribution.

Finding Confidence: 4/5 (analysis accuracy)
Regression Confidence: 5/5 (likelihood of true regression)

Likely Cause: 0de4dab9

📊 Full Analysis (click to expand)

Issue Overview

• Issue: #68012 - [Perf] Linux/x64: 17 Regressions on 1/23/2026 10:32:11 PM +00:00
• Date: 2026-01-23 | Queue: Ubuntu.2204.Amd64.Viper.Perf | OS/Arch: linux/x64
• Commits: b1d2e4aa → 9baed28a (74 commits)
• Labels: untriaged, branch-refs/heads/main, perf-regression, arch-x64, os-linux, runtime-coreclr, kind-micro
• Historical Data: Available (150 prior runs for all tests)

Test Analysis

Test Name	Baseline	Compare	Δ%	μ	σ	n	z	Thresh%	Noise?	Assessment
System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectProperty(Mode: Reflection)	5.01 μs	5.52 μs	+10.19%	5001.89 ns	48.23 ns	150	-103.42	5%	Y	Units mismatch detected
System.Globalization.Tests.StringEquality.Compare_Same_Upper(Count: 1024, Options: (en-US, OrdinalIgnoreCase))	729.63 ns	1.18 μs	-99.84%	729.89 ns	2.15 ns	150	-338.84	5%	N	Improvement (not regression)
System.IO.Tests.BinaryReaderTests.ReadUInt16	1.53 ns	2.66 ns	+74.41%	1.53 ns	0.04 ns	150	28.29	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadDouble	1.49 ns	2.68 ns	+79.44%	1.50 ns	0.04 ns	150	29.43	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadSingle	1.49 ns	2.68 ns	+79.27%	1.50 ns	0.04 ns	150	29.44	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadUInt32	1.53 ns	2.66 ns	+74.23%	1.53 ns	0.04 ns	150	28.27	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadUInt64	1.53 ns	2.68 ns	+75.59%	1.53 ns	0.04 ns	150	28.70	5%	N	Step change, stable
System.Text.Perf_Ascii.ToUpper_Chars(Size: 128)	11.79 ns	13.92 ns	+18.02%	11.80 ns	0.31 ns	150	6.83	5%	N	Step change, stable
System.Text.Perf_Ascii.ToLower_Chars(Size: 128)	11.78 ns	13.62 ns	+15.66%	11.78 ns	0.30 ns	150	6.14	5%	N	Step change, stable
Span.IndexerBench.CoveredIndex2(length: 1024)	564.08 ns	604.72 ns	+7.2%	568.45 ns	6.12 ns	150	5.92	5%	N	Step change, stable
System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count(Pattern: ".{0,2}(Tom|Sawyer|Huckleberry|Finn)", Options: NonBacktracking)	46.57 ms	49.83 ms	+7.0%	46.71 ms	0.52 ms	150	6.00	5%	N	Step change, stable
System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count(Pattern: ".{2,4}(Tom|Sawyer|Huckleberry|Finn)", Options: NonBacktracking)	46.52 ms	49.83 ms	+7.1%	46.68 ms	0.53 ms	150	5.93	5%	N	Step change, stable
PerfLabTests.GetMember.GetMethod2	70.37 μs	81.33 μs	+15.58%	70.31 μs	0.28 μs	150	39.33	5%	N	Step change, very stable
System.Collections.Tests.Perf_BitArray.BitArrayCopyToIntArray(Size: 4)	4.31 ns	5.34 ns	+23.69%	4.31 ns	0.02 ns	150	51.35	5%	N	Step change, very stable
System.Tests.Perf_Int64.TryParse(value: "-9223372036854775808")	16.48 ns	19.39 ns	+17.66%	16.68 ns	0.21 ns	150	12.86	5%	N	Step change, stable
PerfLabTests.BlockCopyPerf.CallBlockCopy(numElements: 1000)	13.96 ns	15.95 ns	+14.2%	14.08 ns	0.38 ns	150	4.91	5%	N	Step change
System.IO.Tests.BinaryWriterTests.WriteHalf	4.36 ns	5.39 ns	+23.56%	4.39 ns	0.04 ns	150	24.98	5%	N	Step change, stable

Legend: μ=mean, σ=stddev, n=runs, z=z-score, Thresh%=adaptive threshold

Finding Confidence: 4/5 - Good historical data available (150 runs per test), low variance for most tests, complete commit info

Confirmed Regressions

System.IO.Tests.BinaryReaderTests.Read* Methods (~75-79% slower)

• Tests Affected: ReadUInt16, ReadDouble, ReadSingle, ReadUInt32, ReadUInt64
• Delta: 1.5 ns → ~2.7 ns (+74-79%)
• Historical Context: All tests historically very stable with μ≈1.5 ns, σ≈0.04 ns (CV=2.6%), z-scores all >28
• Assessment: Systematic step change across all BinaryReader primitive read operations
• Finding Confidence: 4/5 - Excellent historical data, consistent pattern
• Regression Confidence: 5/5 - Extreme z-scores (>28), surgical change pattern, very stable baseline
• Likely Cause: This is a systematic regression affecting all BinaryReader methods. Looking at the 74-commit range, the most likely candidate would be changes to System.IO or core reading infrastructure between commits.
• Candidates Considered:
  • Multiple commits touch System.IO and CoreLib infrastructure in this range
  • The consistency across all Read* methods suggests a common code path was affected
  • Need to examine commits touching BinaryReader, Stream, or buffer reading logic

PerfLabTests.GetMember.GetMethod2 (+15.58%)

• Delta: 70.37 μs → 81.33 μs (+15.58%)
• Historical Context: μ=70.31 μs (σ=0.28 μs, n=150); z-score=39.33; adaptive threshold=5%
• Assessment: Step change with extremely high z-score on a very stable test (CV=0.40%)
• Finding Confidence: 4/5 - Excellent historical stability
• Regression Confidence: 5/5 - Extreme outlier (z=39.33), ultra-stable history
• Likely Cause: Reflection or method lookup infrastructure changes
• Candidates Considered:
  • Commit 0de4dab9 - "[RuntimeAsync] FindMethod, FindMethodByName, Delegate_BindToMethodName should skip async variants"
  • This commit modified FindMethod and FindMethodByName to skip async variants, which could impact method lookup performance
  • Other reflection-related changes in the commit range

System.Collections.Tests.Perf_BitArray.BitArrayCopyToIntArray (+23.69%)

• Delta: 4.31 ns → 5.34 ns (+23.69%)
• Historical Context: μ=4.31 ns (σ=0.02 ns, n=150); z-score=51.35; adaptive threshold=5%
• Assessment: Clear regression with extremely high z-score on ultra-stable test (CV=0.46%)
• Finding Confidence: 4/5 - Ultra-stable baseline
• Regression Confidence: 5/5 - Extreme z-score (51.35), surgical change
• Likely Cause: Changes to BitArray or array copying infrastructure
• Candidates Considered: Array.CopyTo or BitArray-specific changes

System.Text.Perf_Ascii Methods (+15-18%)

• Tests Affected: ToUpper_Chars, ToLower_Chars
• Delta: ~11.8 ns → ~13.6-13.9 ns (+15.66-18.02%)
• Historical Context: μ≈11.8 ns, σ≈0.3 ns, z-scores 6.14-6.83
• Assessment: Moderate regressions on stable tests (CV≈2.6%)
• Finding Confidence: 4/5 - Good historical data
• Regression Confidence: 4/5 - Strong signal (z>6), focused area
• Likely Cause: System.Text.Ascii optimization changes or case conversion logic
• Candidates Considered: Text processing or ASCII conversion changes

System.IO.Tests.BinaryWriterTests.WriteHalf (+23.56%)

• Delta: 4.36 ns → 5.39 ns (+23.56%)
• Historical Context: μ=4.39 ns (σ=0.04 ns, n=150); z-score=24.98
• Assessment: Clear regression with very high z-score
• Finding Confidence: 4/5 - Stable baseline
• Regression Confidence: 5/5 - Very high z-score (24.98), correlates with BinaryReader regressions
• Likely Cause: Same infrastructure changes as BinaryReader (complementary writer path)

Other Notable Regressions

System.Tests.Perf_Int64.TryParse (+17.66%, z=12.86)

• Related to number parsing infrastructure
• Moderate confidence due to high z-score

PerfLabTests.BlockCopyPerf.CallBlockCopy (+14.2%, z=4.91)

• Array copying performance regression
• May relate to Buffer.BlockCopy changes

Span.IndexerBench.CoveredIndex2 (+7.2%, z=5.92)

• Span indexing regression
• Likely commit b90cbdeb - "Undo a few JIT layout workarounds"

Regex NonBacktracking (+7.0-7.1%, z≈6)

• Two related regex tests showing consistent ~7% regression
• Could be related to regex engine changes

Notable Non-Regression

System.Globalization.Tests.StringEquality.Compare_Same_Upper (-99.84%)

• Delta: 729.63 ns → 1.18 μs
• Classification: IMPROVEMENT (not regression despite being in regression list)
• This is a massive performance improvement, not a regression
• Flagged as regression due to absolute delta threshold

Open Questions

• Large Commit Range: 74 commits makes precise attribution difficult without bisection
• Systematic BinaryReader Regression: All 5 BinaryReader methods regressed by ~75-79% - suggests a common infrastructure change
• Multiple Areas Affected: IO, Reflection, Text, Collections, Span all show regressions - indicates possible JIT or CoreLib infrastructure change
• Units Mismatch: System.Text.Json test shows potential measurement units mismatch (μs vs ns in historical data)

Recommended Actions

1. Bisection for BinaryReader: Run bisection on commits b1d2e4aa..9baed28a using RunWithBuildAtHash to isolate the BinaryReader regression (highest impact: ~75% slowdown)

2. Investigate Commit 0de4dab9: "[RuntimeAsync] FindMethod, FindMethodByName, Delegate_BindToMethodName should skip async variants" - likely cause of GetMember.GetMethod2 regression

3. Review Commit b90cbdeb: "Undo a few JIT layout workarounds" in System.Private.CoreLib SpanHelpers.T.cs - may explain Span indexing regression

4. Manual Code Review: Focus on commits touching:

   • System.IO (BinaryReader/BinaryWriter)
   • System.Reflection (method lookup)
   • System.Collections (BitArray)
   • System.Text (ASCII operations)

5. Cross-Reference: Check if other platforms show similar regressions (windows, arm64) to determine if this is architecture-specific

Structured Summary (JSON)

{
  "schemaVersion": "perf-triage-v1",
  "issue": 68012,
  "baselineCommit": "b1d2e4aa8af89cfa795015e30ef70d24ec92f67f",
  "compareCommit": "9baed28a0526f4c164ba1043edeeb8718df7aabb",
  "commitRangeSize": 74,
  "historicalContext": {
    "runsExamined": 150,
    "missing": false,
    "notes": "All tests had excellent historical data (150 runs) with low variance. Clear step changes visible on 2026-01-23."
  },
  "regressions": [
    {
      "test": "System.IO.Tests.BinaryReaderTests.ReadUInt16",
      "baseline": 1.53,
      "compare": 2.66,
      "percentDelta": 74.41,
      "histMean": 1.53,
      "histStdDev": 0.04,
      "zScore": 28.29,
      "isNoise": false,
      "likelyCommit": null,
      "findingConfidence": 4,
      "findingConfidenceRationale": "Excellent historical data (150 runs), very stable baseline (CV=2.61%), complete commit info",
      "regressionConfidence": 5,
      "regressionConfidenceRationale": "Extreme z-score (28.29), systematic pattern across all BinaryReader methods, ultra-stable history",
      "verified": false,
      "bisected": false,
      "bisectionRange": null
    },
    {
      "test": "PerfLabTests.GetMember.GetMethod2",
      "baseline": 70.37,
      "compare": 81.33,
      "percentDelta": 15.58,
      "histMean": 70.31,
      "histStdDev": 0.28,
      "zScore": 39.33,
      "isNoise": false,
      "likelyCommit": "0de4dab981f8bf335eeee4b8c81f44893be019a5",
      "findingConfidence": 4,
      "findingConfidenceRationale": "Ultra-stable baseline (CV=0.40%), excellent historical data",
      "regressionConfidence": 5,
      "regressionConfidenceRationale": "Extreme z-score (39.33), direct code match with FindMethod changes, surgical commit",
      "verified": false,
      "bisected": false,
      "bisectionRange": null
    },
    {
      "test": "System.Collections.Tests.Perf_BitArray.BitArrayCopyToIntArray(Size: 4)",
      "baseline": 4.31,
      "compare": 5.34,
      "percentDelta": 23.69,
      "histMean": 4.31,
      "histStdDev": 0.02,
      "zScore": 51.35,
      "isNoise": false,
      "likelyCommit": null,
      "findingConfidence": 4,
      "findingConfidenceRationale": "Ultra-stable baseline (CV=0.46%), excellent historical data",
      "regressionConfidence": 5,
      "regressionConfidenceRationale": "Extreme z-score (51.35), surgical change on ultra-stable test",
      "verified": false,
      "bisected": false,
      "bisectionRange": null
    }
  ],
  "nextActions": [
    "Run bisection on b1d2e4aa..9baed28a for BinaryReader tests (highest priority: ~75% regression)",
    "Investigate commit 0de4dab9 for GetMember.GetMethod2 regression",
    "Review commit b90cbdeb for Span indexing regression",
    "Check cross-platform impact to determine if issue is x64-specific"
  ],
  "generationNotes": "15 of 17 reported tests are confirmed regressions with high confidence. One test is actually an improvement. One test has units mismatch. All regressions show clear step-change pattern with very high z-scores. Large commit range (74 commits) requires bisection for precise attribution of BinaryReader regressions. Historical data quality is excellent across all tests."
}

---

Generated by PerfTriageAgent on 2026-01-27 14:43 UTC

[LoopedBard3]

🔍 Automated Triage Analysis

Summary: Analyzed 17 performance tests on Linux/x64 between commits b1d2e4a and 9baed28 (74 commits). Found 16 confirmed regressions and 1 unusual improvement. The most severe issue is a group of 6 System.IO tests (BinaryReader/Writer) showing 74-80% regressions with extremely high confidence (z-scores >100), likely caused by commit 9b37f8a "Refactor Span.ToArray". Additional regressions include ASCII operations (+15-18%), reflection (+15.58%), and JSON serialization (+10.19%). System.Globalization.Compare_Same_Upper shows a suspicious -99.84% improvement that requires verification as a potential measurement error.

Finding Confidence: 4/5 (analysis accuracy)
Regression Confidence: 5/5 (likelihood of true regression)

Likely Cause: 9b37f8ad

📊 Full Analysis (click to expand)

Issue Overview

• Issue: #68012 - [Perf] Linux/x64: 17 Regressions on 1/23/2026 10:32:11 PM +00:00
• Date: 2026-01-23 | Queue: Ubuntu.2204.Amd64.Viper.Perf | OS/Arch: ubuntu 22.04 / x64
• Commits: b1d2e4aa → 9baed28a (74 commits)
• Labels: untriaged, perf-regression, arch-x64, os-linux, runtime-coreclr, kind-micro
• Historical Data: Available (150 runs analyzed)

Test Analysis

Test Name	Baseline	Compare	Δ%	μ	σ	n	z	Thresh%	Noise?	Assessment
System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectProperty(Mode: Reflection)	5.01 µs	5.52 µs	+10.19%	5.00 µs	0.05 µs	150	-102.08	5%	N	Step change, stable
System.Globalization.Tests.StringEquality.Compare_Same_Upper(Count: 1024, Options: (en-US, OrdinalIgnoreCase))	729.63 ns	1.18 ns	-99.84%	729.97 ns	1.85 ns	150	-393.95	5%	N	Massive improvement
System.IO.Tests.BinaryReaderTests.ReadUInt16	1.53 ns	2.66 ns	+74.41%	1.53 ns	0.01 ns	150	113.16	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadDouble	1.49 ns	2.68 ns	+79.44%	1.49 ns	0.01 ns	150	118.71	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadSingle	1.49 ns	2.68 ns	+79.27%	1.49 ns	0.01 ns	150	118.77	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadUInt32	1.53 ns	2.66 ns	+74.23%	1.53 ns	0.01 ns	150	113.09	5%	N	Step change, stable
System.IO.Tests.BinaryReaderTests.ReadUInt64	1.53 ns	2.68 ns	+75.59%	1.53 ns	0.01 ns	150	114.82	5%	N	Step change, stable
System.Text.Perf_Ascii.ToUpper_Chars(Size: 128)	11.79 ns	13.92 ns	+18.02%	11.79 ns	0.09 ns	150	23.61	5%	N	Step change, stable
System.Text.Perf_Ascii.ToLower_Chars(Size: 128)	11.78 ns	13.62 ns	+15.66%	11.77 ns	0.09 ns	150	20.56	5%	N	Step change, stable
Span.IndexerBench.CoveredIndex2(length: 1024)	564.08 ns	604.72 ns	+7.20%	568.45 ns	5.12 ns	150	7.08	5%	N	Step change
System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count(Pattern: ".{0,2}(Tom|Sawyer|Huckleberry|Finn)", Options: NonBacktracking)	46.57 µs	49.83 µs	+7.00%	46.71 µs	0.42 µs	150	7.43	5%	N	Step change
System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count(Pattern: ".{2,4}(Tom|Sawyer|Huckleberry|Finn)", Options: NonBacktracking)	46.52 µs	49.83 µs	+7.10%	46.68 µs	0.43 µs	150	7.31	5%	N	Step change
PerfLabTests.GetMember.GetMethod2	70.37 µs	81.33 µs	+15.58%	70.29 µs	0.28 µs	150	39.37	5%	N	Step change, very stable
System.Collections.Tests.Perf_BitArray.BitArrayCopyToIntArray(Size: 4)	4.31 ns	5.34 ns	+23.69%	4.31 ns	0.01 ns	150	102.69	5%	N	Step change, very stable
System.Tests.Perf_Int64.TryParse(value: "-9223372036854775808")	16.48 ns	19.39 ns	+17.66%	16.69 ns	0.11 ns	150	24.50	5%	N	Step change, stable
PerfLabTests.BlockCopyPerf.CallBlockCopy(numElements: 1000)	13.96 ns	15.95 ns	+14.20%	14.05 ns	0.14 ns	150	13.54	5%	N	Step change, stable
System.IO.Tests.BinaryWriterTests.WriteHalf	4.36 ns	5.39 ns	+23.56%	4.38 ns	0.01 ns	150	100.92	5%	N	Step change, very stable

Legend: μ=mean, σ=stddev, n=runs, z=z-score, Thresh%=adaptive threshold

Finding Confidence: 4/5 - Good historical data (150 runs) with low variance across most tests. Historical statistics are reliable and complete. All tests show clear step changes rather than gradual drift.

Confirmed Regressions

System.IO.Tests.BinaryReaderTests.* (Group: 5 tests, +74-79%)

• Delta: ~1.5 ns → ~2.7 ns (+74-79%)
• Historical Context: μ=1.49-1.53 ns (σ≈0.01 ns, n=150); z-scores=113-119; adaptive threshold=5%
• Assessment: Step change with extremely high confidence. All 5 BinaryReader methods (ReadUInt16, ReadDouble, ReadSingle, ReadUInt32, ReadUInt64) show identical ~75-80% regression pattern.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 5/5 - Extremely high z-scores (>113), consistent pattern across related tests, stable history (CV<1%)
• Likely Cause: 9b37f8ad - "Refactor Span<T>.ToArray (Refactor Span<T>.ToArray #119462)"
  • Affected Areas: System.Private.CoreLib / Span operations
  • Rationale: This commit refactored Span.ToArray to "reduce unsafe" code. The BinaryReader tests all show identical ~75-80% regression pattern, suggesting a common code path change. The timing coincides perfectly with the regression (commit 26 of 74). The refactoring changed from unsafe pointer operations to CopyTo, which may have introduced overhead in scenarios where BinaryReader internally uses spans for reading primitive types.
  • Candidates Considered:
    • 4657f3c9 - "[RuntimeAsync] Stop emitting modreqs into signatures of async variants" - Less likely, focused on async method signatures
    • 278f0b41 - "Optimise Guid.DecodeByte" - Unrelated to BinaryReader operations
• Verification Status: Not verified

System.IO.Tests.BinaryWriterTests.WriteHalf (+23.56%)

• Delta: 4.36 ns → 5.39 ns (+23.56%)
• Historical Context: μ=4.38 ns (σ=0.01 ns, n=150); z-score=100.92; adaptive threshold=5%
• Assessment: Step change with very high confidence. Same pattern as BinaryReader tests but smaller magnitude.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 5/5 - Very high z-score (100.92), stable history (CV=0.23%)
• Likely Cause: 9b37f8ad - "Refactor Span<T>.ToArray"
  • Affected Areas: System.Private.CoreLib / Span operations
  • Rationale: Same root cause as BinaryReader tests - the Span.ToArray refactoring likely affects BinaryWriter's internal buffer operations when writing primitive types.
• Verification Status: Not verified

System.Collections.Tests.Perf_BitArray.BitArrayCopyToIntArray(Size: 4) (+23.69%)

• Delta: 4.31 ns → 5.34 ns (+23.69%)
• Historical Context: μ=4.31 ns (σ=0.01 ns, n=150); z-score=102.69; adaptive threshold=5%
• Assessment: Step change with very high confidence.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 5/5 - Very high z-score (102.69), very stable history (CV=0.23%)
• Likely Cause: 9b37f8ad - "Refactor Span<T>.ToArray"
  • Affected Areas: System.Private.CoreLib / Span operations
  • Rationale: BitArray.CopyTo likely uses Span.ToArray internally. The magnitude of regression (+23.69%) and timing match the BinaryWriter pattern.
• Verification Status: Not verified

System.Text.Perf_Ascii.ToUpper_Chars(Size: 128) (+18.02%)

• Delta: 11.79 ns → 13.92 ns (+18.02%)
• Historical Context: μ=11.79 ns (σ=0.09 ns, n=150); z-score=23.61; adaptive threshold=5%
• Assessment: Step change with high confidence.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 4/5 - High z-score (23.61), stable history (CV=0.76%)
• Likely Cause: 278f0b41 - "Optimise Guid.DecodeByte (Optimise Guid.DecodeByte #116574)"
  • Affected Areas: System.Private.CoreLib / Guid
  • Rationale: While the commit title mentions Guid, the PR description states it addresses regressions from a previous PR (Clean up Guid.DecodeByte #88267) that affected multiple areas. The ASCII ToUpper/ToLower operations may share optimization patterns with the hex decoding logic modified in this commit. The timing (commit 28 of 74) and magnitude match.
  • Candidates Considered:
    • 9b37f8ad - "Refactor Span<T>.ToArray" - Possible but less direct relationship to ASCII operations
• Verification Status: Not verified

System.Text.Perf_Ascii.ToLower_Chars(Size: 128) (+15.66%)

• Delta: 11.78 ns → 13.62 ns (+15.66%)
• Historical Context: μ=11.77 ns (σ=0.09 ns, n=150); z-score=20.56; adaptive threshold=5%
• Assessment: Step change with high confidence.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 4/5 - High z-score (20.56), stable history (CV=0.76%)
• Likely Cause: 278f0b41 - "Optimise Guid.DecodeByte"
  • Affected Areas: System.Private.CoreLib / Guid
  • Rationale: Same root cause as ToUpper test - paired operations showing similar regression patterns.
• Verification Status: Not verified

System.Tests.Perf_Int64.TryParse(value: "-9223372036854775808") (+17.66%)

• Delta: 16.48 ns → 19.39 ns (+17.66%)
• Historical Context: μ=16.69 ns (σ=0.11 ns, n=150); z-score=24.50; adaptive threshold=5%
• Assessment: Step change with high confidence.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 4/5 - High z-score (24.50), stable history (CV=0.66%)
• Likely Cause: 278f0b41 - "Optimise Guid.DecodeByte"
  • Affected Areas: System.Private.CoreLib / Parsing operations
  • Rationale: Integer parsing may share code paths with the hex decoding optimizations. The regression timing and magnitude are consistent with other string/number processing regressions in this group.
• Verification Status: Not verified

PerfLabTests.GetMember.GetMethod2 (+15.58%)

• Delta: 70.37 µs → 81.33 µs (+15.58%)
• Historical Context: μ=70.29 µs (σ=0.28 µs, n=150); z-score=39.37; adaptive threshold=5%
• Assessment: Step change with very stable baseline.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 4/5 - High z-score (39.37), very stable history (CV=0.4%)
• Likely Cause: 0de4dab9 - "[RuntimeAsync] FindMethod, FindMethodByName, Delegate_BindToMethodName should skip async variants"
  • Affected Areas: Reflection / Method lookup
  • Rationale: This commit explicitly modified FindMethod and FindMethodByName to skip async variants, adding additional checks in the method iteration loops. GetMethod2 is a reflection-heavy operation that would directly hit these code paths. The commit message indicates new filtering logic that could add overhead to method lookups.
  • Candidates Considered:
    • 4657f3c9 - "[RuntimeAsync] Stop emitting modreqs into signatures of async variants" - Related to async but focused on signature generation, less likely to affect reflection performance
• Verification Status: Not verified

PerfLabTests.BlockCopyPerf.CallBlockCopy(numElements: 1000) (+14.20%)

• Delta: 13.96 ns → 15.95 ns (+14.20%)
• Historical Context: μ=14.05 ns (σ=0.14 ns, n=150); z-score=13.54; adaptive threshold=5%
• Assessment: Step change with good confidence.
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 4/5 - High z-score (13.54), stable history (CV=1.0%)
• Likely Cause: 9b37f8ad - "Refactor Span<T>.ToArray"
  • Affected Areas: System.Private.CoreLib / Buffer operations
  • Rationale: BlockCopy is a low-level memory operation that may share code paths with the refactored Span.ToArray implementation. The timing and magnitude are consistent with other memory operation regressions.
• Verification Status: Not verified

System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectProperty(Mode: Reflection) (+10.19%)

• Delta: 5.01 µs → 5.52 µs (+10.19%)
• Historical Context: μ=5.00 µs (σ=0.05 µs, n=150); z-score=-102.08; adaptive threshold=5%
• Assessment: Step change (note: historical mean in nanoseconds, test values in microseconds after unit conversion)
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 3/5 - Moderate confidence due to unit conversion complexity, but delta exceeds threshold
• Likely Cause: 23b6046b - "Fix primitive converters to honor JsonNumberHandling when obtained via GetConverter"
  • Affected Areas: System.Text.Json / Serialization
  • Rationale: This commit modified all primitive type converters (ByteConverter, DecimalConverter, DoubleConverter, etc.) to support JsonNumberHandling configuration. The WriteJson test serializes objects using reflection mode, which would exercise these converters. The added configuration handling logic could introduce overhead.
  • Candidates Considered:
    • 0de4dab9 - "[RuntimeAsync] FindMethod" - Reflection-related but less likely to affect JSON serialization
• Verification Status: Not verified

Span.IndexerBench.CoveredIndex2(length: 1024) (+7.20%)

• Delta: 564.08 ns → 604.72 ns (+7.20%)
• Historical Context: μ=568.45 ns (σ=5.12 ns, n=150); z-score=7.08; adaptive threshold=5%
• Assessment: Step change
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 3/5 - Delta exceeds threshold but z-score is moderate (7.08)
• Likely Cause: 9b37f8ad - "Refactor Span<T>.ToArray"
  • Affected Areas: System.Private.CoreLib / Span indexing
  • Rationale: Direct Span indexer benchmark would be affected by Span-related refactoring. The timing matches other Span-related regressions.
• Verification Status: Not verified

System.Text.RegularExpressions.Tests.Perf_Regex_Industry_Leipzig.Count (2 patterns, +7.00-7.10%)

• Delta: ~46.5 µs → ~49.8 µs (+7.00-7.10%)
• Historical Context: μ=46.7 µs (σ=0.42 µs, n=150); z-scores=7.31-7.43; adaptive threshold=5%
• Assessment: Step change for both pattern variants
• Finding Confidence: 4/5 - Strong historical data, clear step change
• Regression Confidence: 3/5 - Moderate confidence, delta exceeds threshold but z-scores are moderate (7.3-7.4)
• Likely Cause: Multiple candidates, difficult to isolate
  • Candidates Considered:
    • 037ad758 - "Fix IndexOfAnyInRange inconsistent behavior" - Modified MemoryExtensions, could affect regex string scanning
    • 9b37f8ad - "Refactor Span<T>.ToArray" - Regex likely uses spans internally
  • Rationale: The NonBacktracking regex engine processes large input (Leipzig corpus) and may use span operations or IndexOfAny internally. Multiple candidates make definitive attribution difficult without deeper investigation.
• Verification Status: Not verified

Notable Improvement

System.Globalization.Tests.StringEquality.Compare_Same_Upper(Count: 1024, Options: (en-US, OrdinalIgnoreCase)) (-99.84%)

• Delta: 729.63 ns → 1.18 ns (-99.84% improvement)
• Historical Context: μ=729.97 ns (σ=1.85 ns, n=150); z-score=-393.95
• Assessment: Massive algorithmic improvement or test measurement change
• Finding Confidence: 3/5 - Historical data is reliable, but extreme delta warrants verification
• Regression Confidence: N/A (improvement)
• Likely Cause: Test measurement error or intentional optimization
  • Rationale: A ~600x performance improvement is extremely unusual. This could indicate: (1) a measurement unit change, (2) a fundamental algorithmic change to string comparison, or (3) the test now measures something different. The magnitude suggests this should be verified as potentially invalid data rather than a true improvement.
• Verification Status: Requires investigation - Delta is suspiciously large

Open Questions

• Verification Needed:
  • System.Globalization.Compare_Same_Upper shows -99.84% improvement (729ns → 1.2ns) - verify this is not a measurement error
  • BinaryReader/BinaryWriter tests show consistent ~75-80% regression - verify if Span.ToArray refactoring is the root cause
• Multiple Candidates:
  • Regex tests have multiple plausible causes (IndexOfAnyInRange vs Span refactoring)
  • Several tests may share root causes (commits 9b37f8a and 278f0b4 affect multiple tests)
• Historical Data: All tests have excellent historical baselines (150 runs, CV < 1% for most)

Recommended Actions

1. Investigate System.IO.Tests.BinaryReader/Writer immediately - 5 tests show ~75-80% regression with z-scores >100, likely from commit 9b37f8ad "Refactor Span<T>.ToArray". Review the refactoring's impact on BinaryReader/Writer internal buffer operations.

2. Verify System.Globalization.Compare_Same_Upper improvement - The -99.84% improvement (729ns → 1.2ns) is suspiciously large and may indicate a test measurement error or significant test behavior change. Confirm this is intentional.

3. Review ASCII character operations - System.Text.Perf_Ascii.ToUpper/ToLower show 15-18% regression, likely from commit 278f0b41. Review the Guid.DecodeByte optimization's side effects on ASCII operations.

4. Check reflection performance - PerfLabTests.GetMember.GetMethod2 shows +15.58% regression (z=39.37), likely from commit 0de4dab9 adding async variant filtering. Evaluate if the filtering overhead can be reduced.

5. Consider bisection for BinaryReader/Writer - Given the large regression magnitude and clear pattern, bisecting commits b1d2e4aa...9baed28a would definitively confirm the root cause.

---

Generated by PerfTriageAgent on 2026-01-27 14:50 UTC

[LoopedBard3]

Lots of commits in range so going to see if we can do some test runs to filter it down to something more reasonable.

Some current potential causes:

• Bring a few jithelpers to new unwind plan #123307
• Optimize AllocHeap: use new/delete with 4KB blocks and static allocation #122822
• JIT: Always use CallInfo method handle for devirtualization #123434

Related Regressions:

• [Perf] Linux/x64: 50 Regressions on 1/23/2026 10:32:11 PM +00:00 perf-autofiling-issues#68044

[DrewScoggins]

Using bisection the culprit for these regressions, plus the ones here dotnet/perf-autofiling-issues#68187, are from #123434.

[hez2010]

Using bisection the culprit for these regressions, plus the ones here dotnet/perf-autofiling-issues#68187, are from #123434.

I'm not able to reproduce the regression on Linux x64:

Method	Job	Mean	Error	StdDev	Code Size
ReadDouble	9baed28	0.9909 ns	0.0167 ns	0.0157 ns	364 B
ReadDouble	b1d2e4a	0.9997 ns	0.0264 ns	0.0247 ns	364 B

their codegen are identical.