Regression in System.Text.Json.Tests.Perf_Get.GetDateTime

[performanceautofiler]

Run Information

Architecture	x86
OS	Windows 10.0.18362
Baseline	dd74d3e529bad0da272a473eee48eb127accc15b
Compare	e3860440c151897968eca2227ae98c1912580c44
Diff	Diff

Regressions in System.Text.Encodings.Web.Tests.Perf_Encoders

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio	Baseline ETL	Compare ETL
EncodeUtf16 - Duration of single invocation	25.83 ns	28.71 ns	1.11	0.15	False

Test Report

Repro

git clone https://github.com/dotnet/performance.git
py .\performance\scripts\benchmarks_ci.py -f net6.0 --filter 'System.Text.Encodings.Web.Tests.Perf_Encoders*'

Payloads

Baseline
Compare

Histogram

System.Text.Encodings.Web.Tests.Perf_Encoders.EncodeUtf16(arguments: UnsafeRelaxed,no <escaping /> required,16)

Description of detection logic

IsRegressionChecked: Marked as regression because the three check build points were 0.05 greater than the baseline.
IsImprovementBase: Marked as not an improvement because the compare was not 5% less than the baseline, or the value was too small.
IsRegressionBase: Marked as regression because the compare was 5% greater than the baseline, and the value was not too small.
IsRegressionChecked: Marked as regression because the three check build points were 0.05 greater than the baseline.
IsRegressionWindowed: Marked as regression because 28.71028453319609 > 27.188776668213432.
IsChangePoint: Marked as a change because one of 4/16/2022 5:36:25 PM, 5/6/2022 8:15:32 AM, 5/10/2022 8:56:34 AM falls between 5/1/2022 6:14:18 PM and 5/10/2022 8:56:34 AM.
IsRegressionStdDev: Marked as regression because -27.95515472631434 (T) = (0 -28.77797836917573) / Math.Sqrt((0.14568110947679258 / (45)) + (0.1429620815659853 / (20))) is less than -1.9983405425199077 = MathNet.Numerics.Distributions.StudentT.InvCDF(0, 1, (45) + (20) - 2, .025) and -0.10987211103896709 = (25.92909406673554 - 28.77797836917573) / 25.92909406673554 is less than -0.05.
IsImprovementBase: Marked as not an improvement because the compare was not 5% less than the baseline, or the value was too small.
IsChangeEdgeDetector: Marked not as a regression because Edge Detector said so.

Docs

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

### Run Information

Architecture	x86
OS	Windows 10.0.18362
Baseline	dd74d3e529bad0da272a473eee48eb127accc15b
Compare	e3860440c151897968eca2227ae98c1912580c44
Diff	Diff

Regressions in System.Text.Json.Tests.Perf_Get

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio	Baseline ETL	Compare ETL
GetDateTime - Duration of single invocation	5.54 μs	5.99 μs	1.08	0.02	False

Test Report

Repro

git clone https://github.com/dotnet/performance.git
py .\performance\scripts\benchmarks_ci.py -f net6.0 --filter 'System.Text.Json.Tests.Perf_Get*'

Payloads

Baseline
Compare

Histogram

System.Text.Json.Tests.Perf_Get.GetDateTime

Description of detection logic

IsRegressionChecked: Marked as regression because the three check build points were 0.05 greater than the baseline.
IsImprovementBase: Marked as not an improvement because the compare was not 5% less than the baseline, or the value was too small.
IsRegressionBase: Marked as regression because the compare was 5% greater than the baseline, and the value was not too small.
IsRegressionChecked: Marked as regression because the three check build points were 0.05 greater than the baseline.
IsRegressionWindowed: Marked as regression because 5.992477860601427 > 5.815712837146978.
IsChangePoint: Marked as a change because one of 5/6/2022 8:15:32 AM, 5/10/2022 8:56:34 AM falls between 5/1/2022 6:14:18 PM and 5/10/2022 8:56:34 AM.
IsRegressionStdDev: Marked as regression because -46.53808097630608 (T) = (0 -5977.2266789527885) / Math.Sqrt((1243.9279498020999 / (44)) + (1071.6586271467781 / (21))) is less than -1.9983405425199077 = MathNet.Numerics.Distributions.StudentT.InvCDF(0, 1, (44) + (21) - 2, .025) and -0.07450040593610108 = (5562.796110575174 - 5977.2266789527885) / 5562.796110575174 is less than -0.05.
IsImprovementBase: Marked as not an improvement because the compare was not 5% less than the baseline, or the value was too small.
IsChangeEdgeDetector: Marked not as a regression because Edge Detector said so.

Docs

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

[AndyAyersMS]

GetDateTime regression has persisted, seems like it could be from #68712.

cc @SingleAccretion

[SingleAccretion]

Will take a look.

[SingleAccretion]

Finally started looking at this. The first-order cause is that physical VN removed one CSE, causing the RA to not enregister an argument in a loop. Notably, the overall perfscore of the affected method (JsonHelpers.TryParseDateTimeOffset) improves, as we see better allocation outside said loop.

 G_M19235_IG33:
        cmp      eax, 7
        jge      SHORT G_M19235_IG34
-       mov      edi, dword ptr [ecx+24]
-       lea      edi, [edi+4*edi]
-       add      edi, edi
-       add      edi, ebx
-       add      edi, -48
-       mov      dword ptr [ecx+24], edi
+       mov      ecx, bword ptr [ebp-1CH]
+       mov      ecx, dword ptr [ecx+24]
+       lea      ecx, [ecx+4*ecx]
+       add      ecx, ecx
+       add      ebx, ecx
+       add      ebx, -48
+       mov      ecx, bword ptr [ebp-1CH]
+       mov      dword ptr [ecx+24], ebx
        inc      eax
-                                               ;; size=22 bbWeight=2    PerfScore 11.50
+       mov      bword ptr [ebp-1CH], ecx
+                                               ;; size=31 bbWeight=2    PerfScore 17.50
 G_M19235_IG34:
        inc      edx
+       mov      ecx, bword ptr [ebp-1CH]
        mov      ebx, dword ptr [ebp-14H]
-       mov      edi, bword ptr [ebp-5CH]
                                                ;; size=7 bbWeight=2    PerfScore 4.50
 G_M19235_IG35:
        cmp      edx, ebx
        jge      SHORT G_M19235_IG37
+       mov      bword ptr [ebp-1CH], ecx
        cmp      edx, esi
        jae      G_M19235_IG49
        movzx    ebx, byte  ptr [edi+edx]
-       lea      edi, [ebx-48]
-       cmp      edi, 9
+       lea      ecx, [ebx-48]
+       cmp      ecx, 9
        jbe      SHORT G_M19235_IG33

[AndyAyersMS]

Perf_Encoders was noise

System.Text.Json.Tests.Perf_Get.GetDateTime has persisted. Will transfer this one.