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Optimize left_semi_join by materializing the gather mask #10511

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merged 3 commits into from
May 5, 2022
Merged

Optimize left_semi_join by materializing the gather mask #10511

merged 3 commits into from
May 5, 2022

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cheinger
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@cheinger cheinger commented Mar 24, 2022 •
edited by jrhemstad
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Closes #10464

Updates the left_semi_join to materialize the gather mask instead of generating it via a transform iterator.

Including the map.contains in the gather call reduced occupancy due to increasing register usage. As a result, explicitly materializing the gather mask is faster.

@cheinger cheinger requested a review from a team as a code owner March 24, 2022 20:02
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Can one of the admins verify this patch?

@github-actions github-actions bot added the libcudf Affects libcudf (C++/CUDA) code. label Mar 24, 2022
@cheinger cheinger mentioned this pull request Mar 24, 2022
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@PointKernel PointKernel added improvement Improvement / enhancement to an existing function non-breaking Non-breaking change labels Mar 29, 2022
Optimized left_semi_join
52df19b 
Up to 20x faster. Separated hash table lookup from copy_if because
increased register usage significantly limited occupancy of this
kernel.
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jrhemstad commented Apr 5, 2022 •
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@cheinger so to be clear, the performance improvement didn't come from using cub::DeviceSelect::Flagged, but instead from pulling the map::contains function out of the copy_if by materializing the predicate as a separate array?

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cheinger commented Apr 5, 2022

@jrhemstad correct. I updated the gitlab issue with a more detailed explanation

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@cheinger could you update the PR description to provide a short summary? The PR description goes into the CHANGELOG.

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ok to test

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PointKernel reviewed Apr 5, 2022
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Nice work. Can you please update the PR title accordingly? It would be useful to also include your performance analysis (here) in the PR description. Did you notice any performance changes in semi join benchmarks?

cpp/src/join/semi_join.cu Show resolved Hide resolved
cpp/src/join/semi_join.cu Outdated Show resolved Hide resolved
@PointKernel PointKernel added the Performance Performance related issue label Apr 5, 2022
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sevagh commented Apr 5, 2022

ok to test

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sevagh commented Apr 5, 2022

ok to test

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@PointKernel can you re-review/approve?

@PointKernel PointKernel changed the title Optimize left_semi_join by using cub::DeviceSelect::Flagged instead of thrust::copy_if Optimize left_semi_join by materializing the gather mask May 5, 2022
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add to whitelist

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add to allowlist

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rerun tests

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@gpucibot merge

@rapids-bot rapids-bot bot merged commit ee26fbe into rapidsai:branch-22.06 May 5, 2022
@jrhemstad jrhemstad mentioned this pull request May 26, 2022
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Thank you @cheinger for adding this optimization! I'm seeing a 15-30% reduction in compute time for our JOIN benchmarks as a result of this change.
image

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@GregoryKimball Sweet! Happy to help!

@ttnghia ttnghia mentioned this pull request Jun 23, 2022
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@ttnghia ttnghia mentioned this pull request Jul 6, 2022
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@jrhemstad jrhemstad jrhemstad approved these changes

@PointKernel PointKernel PointKernel approved these changes

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[BUG] Left Semi Join much slower than Inner join
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@cheinger @GPUtester @jrhemstad @PointKernel @sevagh @ajschmidt8 @GregoryKimball