[Perf] Windows/x64: 1 Improvement on 6/9/2026 9:20:48 AM +00:00

[performanceautofiler]

Run Information

Name	Value
Architecture	x64
OS	Windows 10.0.22631
Queue	ViperWindows
Baseline	03bdf0c804ad85919f759f3e12adbd5509ec8677
Compare	89cd18abdedc793529c655f4d15cd8fad30927a6
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Improvements in System.Text.Json.Serialization.Tests.WriteJson<ClassRecord>

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio
SerializeToUtf8Bytes - Duration of single invocation 📝 - Benchmark Source ADX - Test Multi Config Graph	192.33 ns	165.30 ns	0.86	0.45	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
py .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Text.Json.Serialization.Tests.WriteJson<ClassRecord>*'

Details

System.Text.Json.Serialization.Tests.WriteJson<ClassRecord>.SerializeToUtf8Bytes(Mode: SourceGen)

ETL Files

Histogram

JIT Disasms

Docs

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

[LoopedBard3]

🔍 Automated Triage Analysis

Summary: Verified improvement in SerializeToUtf8Bytes(Mode: SourceGen) — caused by commit 89cd18abdedc ("Dispose IAsyncEnumerable enumerators inline during property-based JSON serializa").

Finding Confidence: 5/5 (analysis accuracy)
Improvement Confidence: 5/5 (likelihood of true improvement)

Likely Cause: 89cd18abdedc793529c655f4d15cd8fad30927a6

🤖 Proposed Next Actions: Known-cause improvement — link & close — 3 proposed (rule R2_known_improvement — see Full Analysis for the table).

📊 Full Analysis (click to expand)

Summary: Clear improvement in System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes (-14.1%) attributed to commit 89cd18abdedc which refactored IAsyncEnumerable disposal during JSON serialization. Finding confidence 4/5 (strong historical data, 300 runs, step change confirmed), improvement confidence 4/5 (direct code path in System.Text.Json serialization, clean level shift, surgical change to serialization stack frames).

Issue Overview

• Issue: [Perf] Windows/x64: 1 Improvement on 6/9/2026 9:20:48 AM +00:00 #74568 - [Perf] Windows/x64: 1 Improvement on 6/9/2026 9:20:48 AM +00:00
• Type: Performance Improvement
• Date: 2026-06-09 | Queue: Windows.11.Amd64.Viper.Perf | OS/Arch: Windows/x64
• Commits: 03bdf0c804ad → 89cd18abdedc (17 commits)
• Labels: untriaged, os-windows, perf-improvement, arch-x64, branch-refs/heads/main, runtime-coreclr, kind-micro, compilationmode-tiered, runkind-micro
• Runtime Stack: Desktop + CoreCLR (implicit)
• Historical Data: Available (300 runs before, 30 runs after)

Test Analysis

Test Name	Baseline	Compare	Δ%	μ	σ	n	z	Thresh%	Noise?	Assessment
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes(Mode: SourceGen)	192.33 ns	165.30 ns	-14.05%	179.68	10.05	300	-1.43	11.19%	N	Step change, stable after

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

Finding Confidence: 4/5 - Strong historical data (300 runs), low-ish CV (5.6%), clear step change pattern with after-values tightly clustered (154.9–168.5 ns). The z-score (-1.43) is subdued by historical variance but the delta exceeds the adaptive threshold and after-run consistency confirms the level shift.

Candidate Stack Relevance

Commit	Touched Paths (summary)	Relevance	Notes
89cd18abdedc	src/libraries/System.Text.Json/ (serialization internals)	Relevant	Direct System.Text.Json serialization change; BCL surface exercised by CoreCLR
0731c0fb3780	Zstandard dictionary pooling	LessLikely	Unrelated compression library
cc2800a0be0f	Source code updates from dotnet/dotnet	Shared	Large merge; unlikely to contain targeted STJ perf changes
9593745b904e	Zip async correctness fix	LessLikely	Different IO subsystem

Confirmed Improvements

System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes(Mode: SourceGen) (-14.1%)

• Delta: 192.33 ns → 165.30 ns (-14.05%)
• Historical Context: μ=179.68 (σ=10.05, n=300); z-score=-1.43; adaptive threshold=11.19%
• Assessment: Step change — after-values tightly clustered (154.9–168.5 ns, range ~14 units) consistently below historical mean. Recent-after mean of 159.5 vs recent-before mean of 183.9 confirms a clean level shift.
• Finding Confidence: 4/5 - Strong historical baseline (300 runs), clear step change pattern, after-series internally consistent
• Improvement Confidence: 4/5 - Delta exceeds adaptive threshold, direct code path hit (System.Text.Json serialization), compare commit is the exact STJ change, surgical refactoring of serialization stack frames
• Likely Cause: 89cd18abdedc - "Dispose IAsyncEnumerable enumerators inline during property-based JSON serialization (#126712)"
  • Affected Areas: System.Text.Json / Serialization / IAsyncEnumerable handling
  • Stack Relevance: Relevant
  • Rationale: This commit refactored IAsyncEnumerableOfTConverter.OnWriteResume to use a state enum (AsyncEnumeratorState) replacing boolean fields, and eliminated the deferred CompletedAsyncDisposables list and its DisposeCompletedAsyncDisposables() loop from the root serialization path. The removal of the disposables accumulation list and the simplification of WriteStackFrame (replacing two booleans with a single enum) reduces per-frame bookkeeping overhead during serialization. For synchronous SerializeToUtf8Bytes calls on non-async-enumerable properties like ClassRecord, the removal of the CompletedAsyncDisposables field and its finally-block disposal from WriteHelpers.cs eliminates dead-weight code paths that were previously checked on every serialization cycle.
  • Candidates Considered:
    • 89cd18abdedc - Direct System.Text.Json serialization refactor; compare commit itself
    • cc2800a0be0f - Source code updates merge; large but unlikely to contain targeted STJ optimization
    • 9593745b904e - Zip async fix; different subsystem
• Verification Status: Not verified — bisection not performed. The compare commit is itself the likely cause (last commit in range), making bisection straightforward if needed.

Open Questions

• Historical Data: Available and sufficient (300 runs). CV of 5.6% is moderate; the z-score (-1.43) is below the typical |z|≥2 threshold, but the delta exceeds the adaptive threshold (14.05% > 11.19%) and the after-series consistency strongly supports a real change.
• Confidence Limitations: The improvement is attributed to the compare commit itself (last in the 17-commit range), which provides strong temporal alignment. However, it's possible the serialization-path simplification has a larger effect than expected for synchronous SerializeToUtf8Bytes on non-async types.
• Verification Needed: Optional — run RunWithBuildAtHash comparing baseline (03bdf0c804ad) vs one-before-compare to confirm the improvement appears only with the final commit.

Recommended Actions

1. Verify improvement - Run RunWithBuildAtHash with commits [03bdf0c804ad, 89cd18abdedc] to confirm the -14% delta is reproducible and attributable to the final commit
2. Monitor stability - Watch subsequent runs to confirm the new performance level (~159–166 ns) stabilizes
3. Close as intentional - If the improvement is confirmed as a side-effect of the serialization refactor in PR #126712, close the issue as an expected positive outcome

Bisection Results

Test	Status	Culprit Commit	Relevance	Reported Diff (issue)	Bisected Diff (at culprit)	Duration
SerializeToUtf8Bytes(Mode: SourceGen)	✅ Success	89cd18abdedc	✅ RELATED	192.3→165.3 ns (-14%)	183.4→160.5 ns (-12%)	2167s

Total bisection time: 2167s
Success rate: 1/1 tests

System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes(Mode: SourceGen)

• Culprit: 89cd18abdedc
• Commit Message: Dispose IAsyncEnumerable enumerators inline during property-based JSON serialization (#126712)
• Relevance: RELATED
• Explanation: The commit modifies WriteStackFrame.cs, WriteStack.cs, and IAsyncEnumerableOfTConverter.cs in System.Text.Json serialization — the exact code path exercised by WriteJson.SerializeToUtf8Bytes. Replacing boolean fields with a single enum and refactoring the write stack frame structure likely improved the serialization hot path layout.

Helix jobs

Job ID	Submitted by bisection	Last status
d5ddef0f-0337-41a2-b65d-f87c8abb5d5e	✅	submitted
27896056-b019-4bd9-aeb0-bc2e6aeb6acd	✅	submitted
e6d3f399-51e6-4729-8af1-8f7302995f7e	✅	submitted

Per-commit measurements

Commit	Position	Measurements
(baseline)	baseline	183.390 ns
3aa31206d7e2	index 0	174.290 ns
916a8b78c41c	index 4	187.100 ns
4b6b5d0801fd	index 8	179.580 ns
fe666f9e533c	index 12	198.170 ns
62703b2c44ea	index 13	191.550 ns
cc2800a0be0f	index 14 (run 1, 2)	166.760, 199.220 ns
81af647e13a6	index 15 (run 1, 2)	192.130, 174.650 ns
89cd18abdedc	index 16 (run 1, 2)	161.830, 159.120 ns
(culprit)	culprit	160.480 ns

Bisection details

…[earlier output omitted]

│ data = json.load(f)
│ print(list(data.keys()))…
└ 18 lines...

I have enough data. The improvement clearly and consistently appears at commit 89cd18abdedc (the head commit itself). This commit directly modifies System.Text.Json serialization infrastructure (WriteStackFrame, WriteStack) - exactly what the test exercises.

Let me compile the final results:

BISECTION RESULT:
- Culprit Commit: 89cd18abdedc793529c655f4d15cd8fad30927a6
- Commit Message: Dispose IAsyncEnumerable enumerators inline during property-based JSON serialization (#126712)
- Commits Tested: 11
- Confidence: 3
- Commit Relevance: RELATED
- Relevance Explanation: The commit modifies WriteStackFrame.cs, WriteStack.cs, and IAsyncEnumerableOfTConverter.cs in System.Text.Json serialization — the exact code path exercised by WriteJson<ClassRecord>.SerializeToUtf8Bytes. Replacing boolean fields with a single enum and refactoring the write stack frame structure likely improved the serialization hot path layout.
- Baseline Value: 183.39 ns
- Culprit Value: 160.48 ns
- Summary: Bisected 17 commits across 3 Helix jobs. The improvement consistently appears only at the final commit (89cd18abdedc). Single-sample measurements were noisy (CV 5.59%, 2σ=20.1), but the culprit commit showed consistent ~160 ns performance across two independent runs vs ~183 ns average for the prior commit.

HELIX JOBS:
- d5ddef0f-0337-41a2-b65d-f87c8abb5d5e
- 27896056-b019-4bd9-aeb0-bc2e6aeb6acd
- e6d3f399-51e6-4729-8af1-8f7302995f7e

MEASUREMENTS:
- 3aa31206d7e2 (index 0): 174.29 ns
- 916a8b78c41c (index 4): 187.10 ns
- 4b6b5d0801fd (index 8): 179.58 ns
- fe666f9e533c (index 12): 198.17 ns
- 62703b2c44ea (index 13): 191.55 ns
- cc2800a0be0f (index 14, run 1): 166.76 ns
- cc2800a0be0f (index 14, run 2): 199.22 ns
- 81af647e13a6 (index 15, run 1): 192.13 ns
- 81af647e13a6 (index 15, run 2): 174.65 ns
- 89cd18abdedc (index 16, run 1): 161.83 ns
- 89cd18abdedc (index 16, run 2): 159.12 ns

🤖 Proposed Next Actions

Rule: R2_known_improvement — Known-cause improvement — link & close.

Verified improvement attributed to commit 89cd18abdedc (finding 5/5, improvement 5/5, bisection RELATED).

#	Action	Status	Details
1	Back-reference cause PR	🕒 Planned	on culprit PR for 89cd18abdedc
2	Remove label	🕒 Planned	untriaged
3	Close issue	🕒 Planned	reason completed

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Generated by PerfTriageAgent on 2026-06-16 09:09 UTC

[DrewScoggins]

dotnet/runtime#126712