JuliaGPU / JuliaGPU/CUDA.jl

Base.stack is underperforming.

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good first issue performance
Dominant language
Julia
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Avg merge
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Merged PRs (30d)
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Description

Describe the bug
Stacking arrays of CuArrays is slow.

To reproduce

The Minimal Working Example (MWE) for this bug:

using BenchmarkTools, CUDA;
N=100;
M=1000;
x=randn(N);
x_cu=cu(x);
@btime stack(fill($x,M));
@btime stack(fill($x_cu,M));
@btime cu(stack(fill(collect($x_cu),M)));

As timing I am getting:

70.800 μs (3 allocations: 789.23 KiB)
15.774 ms (8 allocations: 8.19 KiB)
318.900 μs (12 allocations: 399.83 KiB)
Manifest.toml

CUDA v5.1.2

CUDA v5.1.2

Version info

Details on Julia: 1.10

Julia Version 1.10.0
Commit 3120989f39 (2023-12-25 18:01 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 8 × Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, skylake)
  Threads: 1 on 8 virtual cores

Details on CUDA:

CUDA runtime 12.3, artifact installation
CUDA driver 12.0
Unknown NVIDIA driver

CUDA libraries:
- CUBLAS: 12.3.4
- CURAND: 10.3.4
- CUFFT: 11.0.12
- CUSOLVER: 11.5.4
- CUSPARSE: 12.2.0
- CUPTI: 21.0.0
- NVML: missing

Julia packages:
- CUDA: 5.1.2
- CUDA_Driver_jll: 0.7.0+1
- CUDA_Runtime_jll: 0.10.1+0

Toolchain:
- Julia: 1.10.0
- LLVM: 15.0.7

1 device:
  0: NVIDIA GeForce MX150 (sm_61, 1.491 GiB / 2.000 GiB available)

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

No project files or tests are named. Start by running the Julia MWE with BenchmarkTools and inspect the Base.stack path for CuArrays; done means stacking CuArrays no longer has the reported performance gap relative to the comparison cases.

Written by the indexing model from the issue text.

Assessment

Tech stack
julia
Domain
performance
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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