optimize-for-gpu

GPU Optimization for Python with NVIDIA

Treat GPU acceleration as an evidence-driven optimization, not an automatic rewrite. Preserve the
user's numerical and algorithmic contract, measure with representative data, and keep the GPU
version only when synchronized end-to-end benchmarks show a useful improvement.

When This Skill Applies

• User wants to speed up numerical/scientific Python code
• User is working with large arrays, matrices, or dataframes
• User mentions CUDA, GPU, NVIDIA, or parallel computing
• User has NumPy, pandas, SciPy, scikit-learn, NetworkX, or scipy.sparse.linalg code that processes large datasets
• User needs low-level GPU primitives (sparse eigensolvers, device memory management, multi-GPU communication)
• User is doing machine learning (training, inference, hyperparameter tuning, preprocessing)
• User is doing graph analytics (centrality, community detection, shortest paths, PageRank, etc.)
• User is doing vector search, nearest neighbor search, similarity search, or building a RAG pipeline
• User has Faiss, Annoy, ScaNN, or sklearn NearestNeighbors code that could be GPU-accelerated
• User wants GPU-accelerated interactive dashboards, cross-filtering, or exploratory data analysis on large datasets
• User is doing geospatial analysis (point-in-polygon, spatial joins, trajectory analysis, distance calculations) with GeoPandas or shapely
• User is doing image processing, computer vision, or medical imaging (filtering, segmentation, morphology, feature detection) with scikit-image or OpenCV
• User is working with whole-slide images (WSI), digital pathology, microscopy, or remote sensing imagery
• User is loading large binary data files into GPU memory (numpy.fromfile → cupy, or Python open() → GPU array)
• User needs to read files from S3, HTTP, or WebHDFS directly into GPU memory
• User mentions GPUDirect Storage (GDS) or wants to bypass CPU-memory staging for file IO
• User is doing physics simulation (particles, cloth, fluids, rigid bodies) or differentiable simulation
• User needs mesh operations (ray casting, closest-point queries, signed distance fields) or geometry processing on GPU
• User is doing robotics (kinematics, dynamics, control) with transforms and quaternions
• User has Python simulation loops that could be JIT-compiled to GPU kernels
• User mentions NVIDIA Warp or wants differentiable GPU simulation integrated with PyTorch/JAX
• User is doing simulations, signal processing, financial modeling, bioinformatics, physics, or any compute-intensive work
• User wants to optimize existing code and GPU acceleration is the right answer

Choose the Smallest Suitable Layer

Prefer a maintained library implementation over a custom kernel:

Existing workload	Preferred path	Use for
NumPy / SciPy	CuPy	arrays, sparse matrices, linear algebra, FFTs, signal processing
pandas	cudf.pandas, then cuDF	accelerator mode first; native API for more control
scikit-learn	cuml.accel, then cuML	accelerator mode first; native estimators as needed
NetworkX	nx-cugraph, then cuGraph	backend dispatch first; native graph API at scale
scikit-image	cuCIM	GPU image processing and whole-slide imaging
Faiss / Annoy / k-NN	cuVS	exact and approximate vector search
Raw or remote file I/O	KvikIO	GPU buffers and GPUDirect Storage
Custom array kernels	Numba-CUDA-MLIR for new work; Numba-CUDA for existing code	explicit SIMT kernels and shared memory
Spatial or differentiable kernels	Warp	geometry, simulation kernels, robotics, autodiff
High-level physics simulation	Newton	maintained engine that succeeds the removed warp.sim module
Low-level RAPIDS primitives	RAFT (pylibraft)	sparse eigensolvers, resources, multi-GPU building blocks

Do not move code out of PyTorch, JAX, TensorFlow, or another GPU-native framework merely to use
one of these libraries. First remove CPU round trips and use the framework's compiler, profiler,
mixed-precision, and batching facilities.

Treat these as legacy-only:

Project	Status	Guidance
cuxfilter	Final release 26.06	Maintain existing dashboards only. For new work, combine cuDF with HoloViews/hvPlot/Datashader and serve with Panel, Dash, Streamlit, or Bokeh.
cuSpatial	Archived at 25.04	Use only in an isolated legacy environment. For new work, keep geometry in GeoPandas/Shapely and accelerate compatible tabular stages with cuDF.

Full per-library guidance, including when each is the wrong choice and how to combine
them, is in references/decision_framework.md.
Install commands and CUDA version selection are in
references/installation.md. Before/after conversions for
every library are in
references/code_transformation_patterns.md.

Optimization Workflow

1. Define the contract and baseline

• Capture a representative input, expected output, and acceptable numerical tolerance.
• Measure the current end-to-end path, including input, transfers, compute, and output.
• Profile before changing code. Use CPU profilers for CPU code and identify whether the real limit
  is compute, memory bandwidth, allocation, transfer, synchronization, or storage.
• Record hardware, package versions, dtypes, shapes, batch size, and warm-up policy with results.

2. Check suitability before porting

GPU execution is promising when the hot path exposes substantial independent work, runs often
enough to amortize initialization and transfer, and has a working set that fits available device
memory with room for temporaries. Keep a CPU path when the workload is small, mostly sequential,
dominated by unsupported operations, or requires frequent host-device round trips.

Do not use fixed row-count thresholds as proof. Benchmark the user's actual shapes and hardware.
For out-of-core data, estimate peak working memory and choose chunking, Dask, or a streaming design
before allocating.

3. Try the least disruptive implementation

1. If the code already uses a GPU-native framework, optimize within that framework.
2. Try accelerator or backend modes (cudf.pandas, cuml.accel, nx-cugraph).
3. Move to a native GPU API only where accelerator coverage or performance is insufficient.
4. Write a custom kernel only when profiling shows an operation without a suitable library
   implementation.

Read the relevant library reference before writing code; compatible names can still differ in
defaults, dtypes, output types, and supported arguments.

4. Keep a coherent GPU data path

• Transfer inputs once and keep intermediates device-resident.
• Reuse allocations and prefer out= or in-place forms when semantics allow.
• Batch small operations; fuse elementwise work when it removes intermediate arrays.
• Use pinned host memory and non-default streams only after profiling shows transfer overlap matters.
• Choose float32, mixed precision, or reduced-precision storage only when the contract permits it.

5. Validate semantics before speed

• Compare CPU and GPU outputs on small deterministic fixtures and representative data.
• Use explicit tolerances for floating-point results and test edge cases, NaNs, ordering, and dtypes.
• For approximate nearest-neighbor indexes, report recall@k against exact search; do not compare an
  exact CPU algorithm with an approximate GPU algorithm as if they were equivalent.
• Check accelerator warnings and logs for CPU fallback.

6. Benchmark GPU code correctly

GPU work is asynchronous, so a CPU timer around an unsynchronized call measures enqueue time.
Warm up context creation and JIT compilation, then use CUDA events or a library-aware timer:

from cupyx.profiler import benchmark

print(benchmark(gpu_function, (arg1, arg2), n_warmup=10, n_repeat=100))

Use %gpu_timeit in notebooks, Nsight Systems (nsys) for end-to-end timelines, and Nsight
Compute (ncu) for kernel analysis. Report both synchronized kernel/region time and realistic
end-to-end latency; include transfer and conversion costs when production pays them.

7. Keep, revise, or reject the port

Retain the GPU path only when it passes correctness checks and improves the metric the user cares
about on representative data. If it does not, explain whether the limiting factor is problem size,
transfers, unsupported fallback, memory pressure, launch granularity, or the algorithm itself.

Important Notes

• Provide a CPU fallback when the application requires portability; otherwise fail early with a
  clear hardware and dependency error.
• Test numerical correctness against CPU results (GPU floating point may differ slightly due to operation ordering)
• GPU memory is limited — for datasets larger than GPU memory, consider chunking or using RAPIDS Dask for multi-GPU
• Prefer the CUDA Array Interface or DLPack for supported zero-copy interchange, but verify device,
  dtype, contiguity, ownership, and stream semantics rather than assuming every conversion is free.

Reference Files

Before writing any GPU optimization code, read the relevant reference file(s):

File	When to Read
references/cupy.md	User has NumPy/SciPy code, or needs array operations on GPU
references/numba.md	User has existing Numba-CUDA code or needs explicit SIMT kernels; note the migration path to Numba-CUDA-MLIR
references/cudf.md	User has pandas code, or needs dataframe operations on GPU
references/cuml.md	User has scikit-learn code, or needs ML training/inference/preprocessing on GPU
references/cugraph.md	User has NetworkX code, or needs graph analytics on GPU
references/warp.md	User needs GPU kernels for simulation, spatial computing, mesh/volume queries, differentiable programming, or robotics; use Newton for a high-level physics engine
references/kvikio.md	User needs high-performance file IO to/from GPU, GPUDirect Storage, reading S3/HTTP to GPU, or Zarr on GPU
references/cuxfilter.md	User maintains or explicitly requests cuxfilter (sunset — 26.06 is the final release)
references/cucim.md	User has scikit-image code, or needs image processing, digital pathology, or WSI reading on GPU
references/cuvs.md	User needs vector search, nearest neighbors, similarity search, or RAG retrieval on GPU
references/cuspatial.md	User maintains or explicitly requests cuSpatial (archived — frozen at 25.04 and isolated from current RAPIDS)
references/raft.md	User needs sparse eigensolvers, device memory management, or multi-GPU primitives

Read the specific reference before writing code — they contain detailed API patterns, optimization techniques, and pitfalls specific to each library.