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Fix k-means++ root rank race condition #1359

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Merged
rapids-bot merged 4 commits into from
Sep 25, 2025
Merged

Fix k-means++ root rank race condition #1359

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e031af6
Fix k-means++ root rank race condition
csadorf Sep 23, 2025
afd25c9
Update cpp/src/cluster/detail/kmeans_mg.cuh
csadorf Sep 23, 2025
68e7ef7
Fix linter issues.
csadorf Sep 23, 2025
8141f32
Merge branch 'branch-25.10' into fix/cuml-issue-7425
csadorf Sep 24, 2025
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17 changes: 14 additions & 3 deletions cpp/src/cluster/detail/kmeans_mg.cuh
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Original file line number Diff line number Diff line change
Expand Up @@ -175,9 +175,20 @@ void initKMeansPlusPlus(const raft::resources& handle,
// X which will be used as the initial centroid for kmeans++
// 1.3 - Communicate the initial centroid chosen by rank-r' to all other
// ranks
std::mt19937 gen(params.rng_state.seed);
std::uniform_int_distribution<> dis(0, n_rank - 1);
int rp = dis(gen);
// Choose rp on rank 0 and broadcast to all ranks to guarantee agreement
int rp = 0;
if (my_rank == KMEANS_COMM_ROOT) {
std::mt19937 gen(params.rng_state.seed);
std::uniform_int_distribution<> dis(0, n_rank - 1);
rp = dis(gen);
}
{
rmm::device_scalar<int> rp_d(stream);
raft::copy(rp_d.data(), &rp, 1, stream);
comm.bcast<int>(rp_d.data(), 1, /*root=*/KMEANS_COMM_ROOT, stream);
raft::copy(&rp, rp_d.data(), 1, stream);
raft::resource::sync_stream(handle);
}

// buffer to flag the sample that is chosen as initial centroids
std::vector<std::uint8_t> h_isSampleCentroid(n_samples);
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