Regressions in System.Buffers.Text.Tests.Base64EncodeDecodeInPlaceTests

[performanceautofiler]

Run Information

Name	Value
Architecture	x64
OS	ubuntu 18.04
Queue	TigerUbuntu
Baseline	05a3d360d6079db3cb64636fcdf99f832a58c1d2
Compare	bc1175382857c4af11c27b3134fd22dc8377dfb5
Diff	Diff
Configs	CompilationMode:tiered, RunKind:micro

Regressions in System.Buffers.Text.Tests.Base64EncodeDecodeInPlaceTests

Benchmark	Baseline	Test	Test/Base	Test Quality	Edge Detector	Baseline IR	Compare IR	IR Ratio	Baseline ETL	Compare ETL
Base64DecodeInPlace - Duration of single invocation	113.82 ms	143.74 ms	1.26	0.01	True

Test Report

Repro

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

Payloads

Baseline
Compare

git clone https://github.com/dotnet/performance.git
python3 .\performance\scripts\benchmarks_ci.py -f net8.0 --filter 'System.Buffers.Text.Tests.Base64EncodeDecodeInPlaceTests*'

Payloads

Baseline
Compare

Histogram

System.Buffers.Text.Tests.Base64EncodeDecodeInPlaceTests.Base64DecodeInPlace(NumberOfBytes: 200000000)

Description of detection logic

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.
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 143.736245 > 119.5565114153846.
IsChangePoint: Marked as a change because one of 2/24/2023 8:06:06 PM, 5/8/2023 3:52:55 PM, 5/16/2023 7:34:13 AM falls between 5/7/2023 5:11:33 AM and 5/16/2023 7:34:13 AM.
IsRegressionStdDev: Marked as regression because -207.8542267672069 (T) = (0 -144284018.73783883) / Math.Sqrt((31267341672.962914 / (15)) + (484350566709.22046 / (25))) is less than -2.0243941639098457 = MathNet.Numerics.Distributions.StudentT.InvCDF(0, 1, (15) + (25) - 2, .025) and -0.26747237620001 = (113836026.28912087 - 144284018.73783883) / 113836026.28912087 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 as regression because Edge Detector said so.

JIT Disasms

Docs

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

[EgorBo]

Regressed in #85938 cc @stephentoub

[stephentoub]

I'll take a look. We weren't expecting such regressions for existing input.

[gfoidl]

May this come from

runtime/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Decoder.cs

Line 460 in 80ffe5c

sourceIndex = 0;

which now is the out param, and not a local anymore? (So stack vs. register)