2a7ca101d7
Sparse-checkout from NVIDIA/cccl main branch to complete cccl_upstream: Added: - python/cuda_cccl/ (226 files) — Python bindings for device-level algorithms Critical for muh toolchain: cuda.compute.reduce_into, scan, radix_sort, etc. Includes 204 .py files with full test coverage for all 27 algorithms - ci/ (163 files) — Build/test infrastructure build_cub.sh, test_cub.sh, build_and_test_targets.sh, matrix.yaml Directly maps to our [INFRA-CI] and [INFRA-BUILD] items - .agent/skills/ (7 files) — NVIDIA's own agent skills for CCCL cccl-style/SKILL.md, cccl-test/SKILL.md, sass-diff/SKILL.md - docs/ (491 files) — Official CCCL documentation CI references, CMake guides, Python compute docs, libcudacxx PTX docs - test/ (12 files) — Top-level integration tests (cuda_smoke, stdpar) - Root configs: .clang-format, .clang-tidy, CONTRIBUTING.md, pyproject.toml - CLAUDE.md symlink → AGENTS.md (NVIDIA's standard) cccl_upstream now mirrors full NVIDIA/cccl structure: Before: 42M (cub + thrust + libcudacxx + cudax + c + examples + benchmarks) After: 53M (+python +ci +docs +.agent +test +configs) This completes the CCCL base needed for: - [muh-bench] items: ci/util/build_and_test_targets.sh for targeted builds - [CCCL-verify] items: python/cuda_cccl/tests/ as reference implementations - [CCCL-test] items: ci/test_cub.sh, ci/test_thrust.sh - Agent workflow: .agent/skills/ for consistent style and test patterns
77 lines
2.8 KiB
ReStructuredText
77 lines
2.8 KiB
ReStructuredText
.. _cub-determinism:
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Determinism
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===============
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Several ``cub`` device algorithms let you request a reproducibility guarantee for a call. The concepts
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behind the three guarantees — ``not_guaranteed``, ``run_to_run``, and ``gpu_to_gpu`` — and the meaning
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of *reproducibility* are described in the :ref:`CCCL determinism overview <cccl-determinism>`. This
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page documents how to request a guarantee for a CUB algorithm and which algorithms support which
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guarantees.
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Requesting a guarantee
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----------------------
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A determinism guarantee is passed to a device algorithm through its execution environment using
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``cuda::execution::require``. The example below requests run-to-run reproducibility for
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``cub::DeviceReduce::Sum``:
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.. literalinclude:: ../../cub/test/catch2_test_device_reduce_env_api.cu
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:language: c++
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:dedent:
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:start-after: example-begin sum-env-determinism
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:end-before: example-end sum-env-determinism
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The general rules for requesting a guarantee are described in the
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:ref:`CCCL determinism overview <cccl-determinism>`.
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Each CUB algorithm has its own default guarantee, applied when none is requested, and its own type and
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operator constraints for each guarantee, summarized below. Requesting a guarantee that an algorithm
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does not support is rejected at compile time.
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Support matrix
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--------------
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.. list-table::
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:header-rows: 1
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:widths: 30 18 18 18 16
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* - Algorithm
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- ``not_guaranteed``
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- ``run_to_run``
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- ``gpu_to_gpu``
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- Default
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* - ``cub::DeviceReduce`` (``Reduce``, ``Sum``, ``Min``, ``Max``, ``TransformReduce``, ...)
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- Yes
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- Yes
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- Yes (partial)
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- ``run_to_run``
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* - ``cub::DeviceScan`` (``ExclusiveSum``, ``ExclusiveScan``, ``InclusiveSum``, ``InclusiveScan``, ...)
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- Yes
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- Yes (partial)
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- Yes (partial)
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- ``not_guaranteed``
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* - ``cub::DeviceSegmentedReduce``
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- Yes
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- Yes
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- No
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- ``run_to_run``
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.. note::
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The set of algorithms that accept determinism requirements, and the type/operator constraints for
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each guarantee, are expanding over time. The matrix above reflects the current implementation.
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Algorithm-specific determinism models
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--------------------------------------
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The three guarantees describe the *scope* of reproducibility and fit most algorithms, where a
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reproducible result means a *bitwise-identical* output. A few algorithms still use the same three
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levels but extend the model with additional, algorithm-specific controls, documented on their own
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pages:
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- :ref:`cub::DeviceTopK <cub-topk-requirements>` — determinism applies to *set membership* (which
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*K* items are selected) rather than a bitwise-identical buffer, and it adds tie-breaking
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(``cuda::execution::tie_break``) and output-ordering (``cuda::execution::output_ordering``)
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controls.
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