[WIP] ANNs for clustering at training time

cpp/bench/ann/CMakeLists.txt

@@ -278,6 +278,57 @@ if(CUVS_KNN_BENCH_USE_CUVS_BRUTE_FORCE)
   )
 endif()
 
+# Cluster assignment benchmark: brute force vs CAGRA for assigning vectors to clusters (IVF
+# training)
+if(CUVS_ANN_BENCH_USE_CUVS_CAGRA)
+  add_executable(CUVS_CLUSTER_ASSIGNMENT_BENCH src/cuvs/cuvs_cluster_assignment_bench.cu)
+  target_link_libraries(
+    CUVS_CLUSTER_ASSIGNMENT_BENCH
+    PRIVATE cuvs benchmark::benchmark $<$<TARGET_EXISTS:CUDA::nvtx3>:CUDA::nvtx3>
+            $<COMPILE_ONLY:nvidia::cutlass::cutlass>
+  )
+  target_include_directories(
+    CUVS_CLUSTER_ASSIGNMENT_BENCH
+    PUBLIC "$<BUILD_INTERFACE:${CUVS_SOURCE_DIR}/include>"
+           "$<BUILD_INTERFACE:${CUVS_SOURCE_DIR}/../c/include>"
+    PRIVATE "$<BUILD_INTERFACE:${CUVS_SOURCE_DIR}/src>"
+  )
+  set_target_properties(
+    CUVS_CLUSTER_ASSIGNMENT_BENCH
+    PROPERTIES CXX_STANDARD 17
+               CXX_STANDARD_REQUIRED ON
+               CUDA_STANDARD 17
+               CUDA_STANDARD_REQUIRED ON
+  )
+  install(
+    TARGETS CUVS_CLUSTER_ASSIGNMENT_BENCH
+    COMPONENT ann_bench
+    DESTINATION bin/ann
+  )
+  add_dependencies(CUVS_ANN_BENCH_ALL CUVS_CLUSTER_ASSIGNMENT_BENCH)
+
+  # IVF-PQ build benchmarks: k-means fit and extend cluster-assignment (brute vs CAGRA)
+  add_executable(CUVS_IVFPQ_BUILD_BENCH src/cuvs/cuvs_ivf_pq_build_bench.cu)
+  target_link_libraries(CUVS_IVFPQ_BUILD_BENCH PRIVATE cuvs benchmark::benchmark)
+  target_include_directories(
+    CUVS_IVFPQ_BUILD_BENCH PUBLIC "$<BUILD_INTERFACE:${CUVS_SOURCE_DIR}/include>"
+                                  "$<BUILD_INTERFACE:${CUVS_SOURCE_DIR}/../c/include>"
+  )
+  set_target_properties(
+    CUVS_IVFPQ_BUILD_BENCH
+    PROPERTIES CXX_STANDARD 17
+               CXX_STANDARD_REQUIRED ON
+               CUDA_STANDARD 17
+               CUDA_STANDARD_REQUIRED ON
+  )
+  install(
+    TARGETS CUVS_IVFPQ_BUILD_BENCH
+    COMPONENT ann_bench
+    DESTINATION bin/ann
+  )
+  add_dependencies(CUVS_ANN_BENCH_ALL CUVS_IVFPQ_BUILD_BENCH)
+endif()
+
 if(CUVS_ANN_BENCH_USE_CUVS_CAGRA)
   ConfigureAnnBench(
     NAME

cpp/bench/ann/src/cuvs/cuvs_cluster_assignment_bench.cu

@@ -0,0 +1,292 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2025-2026, NVIDIA CORPORATION.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Benchmark: brute force vs CAGRA-based cluster assignment for IVF training.
+ * Compares time to assign N vectors to K clusters (nearest centroid) using
+ * (1) brute force 1-NN and (2) CAGRA build on centroids + k=1 search.
+ */
+#include <benchmark/benchmark.h>
+
+// kmeans_balanced.cuh is under cpp/src/; CUVS_CLUSTER_ASSIGNMENT_BENCH adds that to include path
+#include <cluster/kmeans_balanced.cuh>
+#include <cuvs/cluster/kmeans.hpp>
+#include <raft/core/device_mdarray.hpp>
+#include <raft/core/device_resources.hpp>
+#include <raft/core/resources.hpp>
+#include <raft/matrix/init.cuh>
+#include <raft/random/rng.cuh>
+#include <raft/random/rng_state.hpp>
+#include <raft/util/cudart_utils.hpp>
+
+#include <cuvs/neighbors/cagra.hpp>
+#include <rmm/device_uvector.hpp>
+
+#include <optional>
+
+namespace {
+
+using namespace cuvs::cluster::kmeans_balanced;
+
+void init_random_data(raft::resources const& handle,
+                      float* X,
+                      int64_t n_rows,
+                      int64_t dim,
+                      float* centroids,
+                      int64_t n_clusters)
+{
+  raft::random::RngState rng(12345ULL);
+  raft::random::uniform(handle, rng, X, n_rows * dim, float(-1), float(1));
+  raft::random::uniform(handle, rng, centroids, n_clusters * dim, float(-1), float(1));
+  raft::resource::sync_stream(handle);
+}
+
+}  // namespace
+
+static void BM_ClusterAssignment_BruteForce(benchmark::State& state)
+{
+  int64_t n_rows     = static_cast<int64_t>(state.range(0));
+  int64_t n_clusters = static_cast<int64_t>(state.range(1));
+  int64_t dim        = static_cast<int64_t>(state.range(2));
+
+  raft::device_resources handle;
+  rmm::device_uvector<float> X(static_cast<size_t>(n_rows) * static_cast<size_t>(dim),
+                               raft::resource::get_cuda_stream(handle));
+  rmm::device_uvector<float> centroids(static_cast<size_t>(n_clusters) * static_cast<size_t>(dim),
+                                       raft::resource::get_cuda_stream(handle));
+  rmm::device_uvector<uint32_t> labels(static_cast<size_t>(n_rows),
+                                       raft::resource::get_cuda_stream(handle));
+
+  init_random_data(handle, X.data(), n_rows, dim, centroids.data(), n_clusters);
+
+  cuvs::cluster::kmeans::balanced_params params;
+  params.metric = cuvs::distance::DistanceType::L2Expanded;
+
+  auto X_view = raft::make_device_matrix_view<const float, int64_t>(X.data(), n_rows, dim);
+  auto centers_view =
+    raft::make_device_matrix_view<const float, int64_t>(centroids.data(), n_clusters, dim);
+  auto labels_view = raft::make_device_vector_view<uint32_t, int64_t>(labels.data(), n_rows);
+
+  for (auto _ : state) {
+    predict(handle, params, X_view, centers_view, labels_view);
+    raft::resource::sync_stream(handle);
+  }
+  state.SetItemsProcessed(state.iterations() * n_rows);
+}
+
+static void BM_ClusterAssignment_CAGRA(benchmark::State& state)
+{
+  int64_t n_rows     = static_cast<int64_t>(state.range(0));
+  int64_t n_clusters = static_cast<int64_t>(state.range(1));
+  int64_t dim        = static_cast<int64_t>(state.range(2));
+
+  raft::device_resources handle;
+  rmm::device_uvector<float> X(static_cast<size_t>(n_rows) * static_cast<size_t>(dim),
+                               raft::resource::get_cuda_stream(handle));
+  rmm::device_uvector<float> centroids(static_cast<size_t>(n_clusters) * static_cast<size_t>(dim),
+                                       raft::resource::get_cuda_stream(handle));
+  rmm::device_uvector<uint32_t> labels(static_cast<size_t>(n_rows),
+                                       raft::resource::get_cuda_stream(handle));
+
+  init_random_data(handle, X.data(), n_rows, dim, centroids.data(), n_clusters);
+
+  cuvs::cluster::kmeans::balanced_params params;
+  params.metric = cuvs::distance::DistanceType::L2Expanded;
+
+  // Same timing as assign_nearest_centroid_cagra_with_index_reuse with rebuild=true each iteration.
+  // float X/centroids only.
+  std::optional<cuvs::neighbors::cagra::index<float, uint32_t>> cagra_index_opt;
+
+  for (auto _ : state) {
+    cuvs::cluster::kmeans::detail::assign_nearest_centroid_cagra_with_index_reuse<int64_t,
+                                                                                  uint32_t>(
+      handle,
+      params,
+      centroids.data(),
+      n_clusters,
+      dim,
+      X.data(),
+      n_rows,
+      labels.data(),
+      &cagra_index_opt,
+      true);
+    raft::resource::sync_stream(handle);
+  }
+  state.SetItemsProcessed(state.iterations() * n_rows);
+}
+
+// N = vectors to assign, K = number of clusters, D = dimension
+// Small: 10K vectors, 1K clusters, 128 dim
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({10000, 1000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({10000, 1000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// Medium: 100K vectors, 4K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({100000, 4000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({100000, 4000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// Large K: 100K vectors, 16K clusters (brute force starts to hurt)
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({100000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({100000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// Very large K: 500K vectors, 64K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({500000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({500000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// Larger N: amortize CAGRA build over more queries
+// 1M vectors, 4K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({1000000, 4000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({1000000, 4000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 1M vectors, 16K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({1000000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({1000000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 1M vectors, 64K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({1000000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({1000000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 2M vectors, 16K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({2000000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({2000000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 2M vectors, 64K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({2000000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({2000000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 5M vectors, 16K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({5000000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({5000000, 16000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 5M vectors, 64K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({5000000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({5000000, 65536, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// Hundreds of thousands of centroids (K = 100K, 200K, 500K, 1M)
+// 1M vectors, 100K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({1000000, 100000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({1000000, 100000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 2M vectors, 100K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({2000000, 100000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({2000000, 100000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 1M vectors, 200K clusters
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({1000000, 200000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({1000000, 200000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 1M vectors, 500K clusters (~2 vectors per cluster)
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({1000000, 500000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({1000000, 500000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 1M clusters with N > K (realistic: many vectors per cluster)
+// 2M vectors, 1M clusters (~2 per cluster)
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({2000000, 1000000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({2000000, 1000000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+// 5M vectors, 1M clusters (~5 per cluster)
+BENCHMARK(BM_ClusterAssignment_BruteForce)
+  ->Args({5000000, 1000000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+BENCHMARK(BM_ClusterAssignment_CAGRA)
+  ->Args({5000000, 1000000, 128})
+  ->Unit(benchmark::kMillisecond)
+  ->UseRealTime();
+
+BENCHMARK_MAIN();