Speed up libcudf examples and avoid JIT cache preloading

[vyasr]

Description

This PR contains four distinct sets of changes:

1. Consistent with our general policy changes across RAPIDS, use the async rather than pool allocator in the examples. This also removes the need for preallocating a large pool up front..
2. Reduce multifile hybrid-scan source counts from ten to four. The two threads still process multiple files, preserving the IO modes, filters, iterations, and invocations exercised by CI.
3. Validate the final benchmark outputs in the ordinary hybrid-scan and pipeline examples instead of performing extra reads.
4. Stop enabling JIT cache preloading in PR and nightly C++ test workflows. Disk caching remains enabled, but kernels are loaded on demand instead of all preloaded at once. This change turned out to have the biggest impact, but the issue was particularly evident when looking at the examples because each run of an example was a separate executable preloading the cache, which therefore magnified the cost dramatically.

Measured CI impact

The impact first three points above were all benchmarked concurrently prior to the change to JIT cache preloading (I didn't notice the preloading impact until after I had applied these other changes). The impact is shown in the below table:

GPU / CUDA	Before	After	Time saved
V100 / 12.2	114.1s	100.2s	13.9s (12.1%)
ARM A100 / 12.2	146.9s	116.5s	30.5s (20.7%)
H100 / 12.9	99.2s	92.3s	6.8s (6.9%)
ARM L4 / 13.0	102.3s	94.4s	7.8s (7.6%)
RTX Pro 6000 / 13.0	34.5s	33.3s	1.2s (3.4%)
RTX Pro 6000 / 13.3	59.8s	80.0s	-20.2s (-33.8%)
Sum across matrix	556.8s	516.8s	39.9s (7.2%)

After the above, I profiled and noted the impact of preloading, so I tested out removing it in CI. The impact was actually much larger in CI than it was locally, which suggests to me that (as we've been seeing on a few other fronts recently) slow disk access in CI is probably making the preload extra expensive (and is also likely leading to I/O contention, making a bad situation even worse). Once I saw the impact the change had on examples, I also tried applying the change to the test runs. The table below includes both timings. The example comparison uses the preload-enabled run, attempt 2 and the preload-disabled examples run for comparison. The libcudf CTest comparison uses that latter run as its preload-enabled test baseline and the preload-disabled test run for the after.

GPU / CUDA	Examples: preload on → off	Saved	libcudf CTest: preload on → off	Saved
V100 / 12.2	109.5s → 41.7s	67.7s (61.9%)	318.7s → 235.3s	83.4s (26.2%)
ARM A100 / 12.2	105.4s → 53.5s	51.9s (49.3%)	324.4s → 213.0s	111.4s (34.3%)
H100 / 12.9	78.1s → 34.5s	43.7s (55.9%)	352.9s → 227.4s	125.5s (35.6%)
ARM L4 / 13.0	71.9s → 33.7s	38.2s (53.1%)	322.9s → 176.3s	146.6s (45.4%)
RTX Pro 6000 / 13.0	34.4s → 9.8s	24.6s (71.6%)	187.3s → 146.6s	40.7s (21.7%)
RTX Pro 6000 / 13.3	68.8s → 9.1s	59.8s (86.8%)	263.3s → 122.2s	141.1s (53.6%)
Sum across matrix	468.1s → 182.2s	285.9s (61.1%)	1769.5s → 1120.9s	648.7s (36.7%)

Interestingly, even JIT-heavy test binaries like AST, Parquet, join, and transform/LTO executable times improved on every matrix entry.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[vyasr]

/ok to test

[vyasr]

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[vyasr]

/ok to test

[vyasr]

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[vyasr]

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[vyasr]

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[vyasr]

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[vyasr]

/ok to test

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• cpp/examples/nested_types/README.md

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📝 Summary

Summary by CodeRabbit

• Updates
  • C++ examples now use CUDA’s asynchronous memory resource instead of configurable pool-based options.
  • Hybrid scan benchmarks retain results for comparison and rerun reads when needed, including for verbose output.
  • Hybrid scan examples use a smaller argument value, and test jobs no longer preload the kernel cache.

📝 Summary

Walkthrough

Example programs now use CUDA async memory resources instead of configurable or pooled CUDA resources. Hybrid-scan benchmarks retain timed table results and use conditional follow-up reads. CI example invocations change their second argument to 4, and C++ test workflows no longer set the kernel-cache preload variable.

Changes

Example Resource and Benchmark Updates

Layer / File(s)	Summary
Async resource helpers and call sites cpp/examples/billion_rows/*, cpp/examples/hybrid_scan_io/common_utils.*, cpp/examples/hybrid_scan_io/hybrid_scan_multifile_*.cpp, cpp/examples/parquet_inspect/*, cpp/examples/parquet_io/*	Resource helpers remove pool-selection options and return CUDA async memory resources. Their callers use the updated interfaces.
Direct example resource setup cpp/examples/basic/src/process_csv.cpp, cpp/examples/nested_types/deduplication.cpp, cpp/examples/nested_types/README.md, cpp/examples/pack_unpack/pack_unpack.cpp, cpp/examples/string_transforms/common.hpp, cpp/examples/strings/common.hpp	These examples replace pool or CUDA resource selection with CUDA async memory resources. String transforms accepts async and async-stats. The deduplication README reflects the updated invocation.
Hybrid-scan benchmark results cpp/examples/hybrid_scan_io/hybrid_scan_io.cpp, cpp/examples/hybrid_scan_io/hybrid_scan_pipeline.cpp, ci/run_cudf_examples.sh	Benchmarks retain timed table results and conditionally rerun readers for verbose output or missing results. Four multifile scan invocations change their second argument from 10 to 4.

C++ Test Cache Settings

Layer / File(s)	Summary
Remove cache preload setting .github/workflows/pr.yaml, .github/workflows/test.yaml	The C++ test jobs retain their cache path settings and no longer set LIBCUDF_KERNEL_CACHE_PRELOAD=1.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

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Merge Risk: ⚪ Minimal · up to e0e35

No actionable merge-blocking risk is established for this change.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 23 files. (1 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly summarizes the two primary changes: speeding up libcudf examples and disabling JIT cache preloading.
Description check		The description is directly related to the changeset and explains the allocator updates, reduced multifile inputs, benchmark validation changes, cache-preloading change, and measured CI impact.

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Full details: Docstring Coverage

Explanation

Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 23 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 1

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Inline comments:
Review comments at @cpp/examples/nested_types/deduplication.cpp:
- Line 146: Update the deduplication README command to omit the obsolete pool
argument, and change its default-resource description from pool to async. Use
the argument check in the deduplication example as the reference for the current
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📥 Commits

Reviewing files that changed from the base of the PR and between 5c2c5fe and 14553a1.

📒 Files selected for processing (25)

• .github/workflows/pr.yaml
• .github/workflows/test.yaml
• ci/run_cudf_examples.sh
• cpp/examples/basic/src/process_csv.cpp
• cpp/examples/billion_rows/brc.cpp
• cpp/examples/billion_rows/brc_chunks.cpp
• cpp/examples/billion_rows/brc_pipeline.cpp
• cpp/examples/billion_rows/common.hpp
• cpp/examples/hybrid_scan_io/common_utils.cpp
• cpp/examples/hybrid_scan_io/common_utils.hpp
• cpp/examples/hybrid_scan_io/hybrid_scan_io.cpp
• cpp/examples/hybrid_scan_io/hybrid_scan_multifile_single_step.cpp
• cpp/examples/hybrid_scan_io/hybrid_scan_multifile_two_step.cpp
• cpp/examples/hybrid_scan_io/hybrid_scan_pipeline.cpp
• cpp/examples/nested_types/deduplication.cpp
• cpp/examples/pack_unpack/pack_unpack.cpp
• cpp/examples/parquet_inspect/parquet_inspect.cpp
• cpp/examples/parquet_inspect/parquet_inspect_utils.cpp
• cpp/examples/parquet_inspect/parquet_inspect_utils.hpp
• cpp/examples/parquet_io/common_utils.cpp
• cpp/examples/parquet_io/common_utils.hpp
• cpp/examples/parquet_io/parquet_io.cpp
• cpp/examples/parquet_io/parquet_io_multithreaded.cpp
• cpp/examples/string_transforms/common.hpp
• cpp/examples/strings/common.hpp

💤 Files with no reviewable changes (2)

• .github/workflows/pr.yaml
• .github/workflows/test.yaml

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