dotnet/runtime

Span<ReferenceType>.CopyTo is 10-20% slower than Array<ReferenceType>.CopyTo

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#29,093 opened on Mar 27, 2019

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 (21 comments) (3 reactions) (0 assignees)C# (5,445 forks)batch import
area-CodeGen-coreclrhelp wantedtenet-performance

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Description

How to run the benchmarks:

git clone https://github.com/dotnet/performance.git
# if you have .NET Core 3.0 installed
dotnet run -c Release -f netcoreapp3.0 -p .\performance\src\benchmarks\micro\MicroBenchmarks.csproj --filter *CopyTo<String>*.Array *CopyTo<String>.Span --join --affinity 2
# if you don't have .NET Core 3.0 installed
py .\performance\scripts\benchmarks_ci.py -f netcoreapp3.0 --filter *CopyTo<String>*.Array *CopyTo<String>.Span --bdn-arguments="--join true --affinity 2"
Method Size Mean
Array 2048 511.1 ns
Span 2048 609.9 ns

Full docs for the new benchmarking workflow: https://github.com/dotnet/performance/blob/master/docs/benchmarking-workflow-corefx.md

category:cq theme:optimization skill-level:expert cost:medium

Contributor guide

Research direction
Investigate the implementation of Span<ReferenceType>.CopyTo and Array<ReferenceType>.CopyTo in the dotnet/runtime repository. Compare the JIT generated code for both methods to identify the performance gap. Focus on bounds checking, type checking, and loop structure. Consider removing redundant checks or using intrinsics.
Tech stack
csharp
Domain
performance
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Span<T>BenchmarkingOptimization
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15