Convert non-type template parameters to runtime parameters in CAGRA search to cut binary size

cpp/src/neighbors/detail/cagra/cagra_search.cuh

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2023-2025, NVIDIA CORPORATION.
+ * SPDX-FileCopyrightText: Copyright (c) 2023-2026, NVIDIA CORPORATION.
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -9,7 +9,6 @@
 #include "factory.cuh"
 #include "sample_filter_utils.cuh"
 #include "search_plan.cuh"
-#include "search_single_cta_inst.cuh"
 
 #include <raft/core/device_mdspan.hpp>
 #include <raft/core/host_mdspan.hpp>

cpp/src/neighbors/detail/cagra/search_multi_cta_kernel-inl.cuh

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2023-2025, NVIDIA CORPORATION.
+ * SPDX-FileCopyrightText: Copyright (c) 2023-2026, NVIDIA CORPORATION.
  * SPDX-License-Identifier: Apache-2.0
  */
 #pragma once
@@ -114,14 +114,14 @@ RAFT_DEVICE_INLINE_FUNCTION void topk_by_bitonic_sort(float* distances,  // [num
                                                       INDEX_T* indices,  // [num_elements]
                                                       const uint32_t num_elements)
 {
-  const unsigned warp_id = threadIdx.x / 32;
+  const unsigned warp_id = threadIdx.x / raft::warp_size();
   if (warp_id > 0) { return; }
-  const unsigned lane_id = threadIdx.x % 32;
-  constexpr unsigned N   = (MAX_ELEMENTS + 31) / 32;
+  const unsigned lane_id = threadIdx.x % raft::warp_size();
+  constexpr unsigned N   = (MAX_ELEMENTS + (raft::warp_size() - 1)) / raft::warp_size();
   float key[N];
   INDEX_T val[N];
   for (unsigned i = 0; i < N; i++) {
-    unsigned j = lane_id + (32 * i);
+    unsigned j = lane_id + (raft::warp_size() * i);
     if (j < num_elements) {
       key[i] = distances[j];
       val[i] = indices[j];
@@ -142,13 +142,34 @@ RAFT_DEVICE_INLINE_FUNCTION void topk_by_bitonic_sort(float* distances,  // [num
   }
 }
 
+RAFT_DEVICE_INLINE_FUNCTION void topk_by_bitonic_sort_wrapper_64(
+  float* distances,   // [num_elements]
+  uint32_t* indices,  // [num_elements]
+  const uint32_t num_elements)
+{
+  topk_by_bitonic_sort<64, uint32_t>(distances, indices, num_elements);
+}
+
+RAFT_DEVICE_INLINE_FUNCTION void topk_by_bitonic_sort_wrapper_128(
+  float* distances,   // [num_elements]
+  uint32_t* indices,  // [num_elements]
+  const uint32_t num_elements)
+{
+  topk_by_bitonic_sort<128, uint32_t>(distances, indices, num_elements);
+}
+
+RAFT_DEVICE_INLINE_FUNCTION void topk_by_bitonic_sort_wrapper_256(
+  float* distances,   // [num_elements]
+  uint32_t* indices,  // [num_elements]
+  const uint32_t num_elements)
+{
+  topk_by_bitonic_sort<256, uint32_t>(distances, indices, num_elements);
+}
+
 //
 // multiple CTAs per single query
 //
-template <std::uint32_t MAX_ELEMENTS,
-          class DATASET_DESCRIPTOR_T,
-          class SourceIndexT,
-          class SAMPLE_FILTER_T>
+template <class DATASET_DESCRIPTOR_T, class SourceIndexT, class SAMPLE_FILTER_T>
 RAFT_KERNEL __launch_bounds__(1024, 1) search_kernel(
   typename DATASET_DESCRIPTOR_T::INDEX_T* const
     result_indices_ptr,  // [num_queries, num_cta_per_query, itopk_size]
@@ -157,6 +178,7 @@ RAFT_KERNEL __launch_bounds__(1024, 1) search_kernel(
   const DATASET_DESCRIPTOR_T* dataset_desc,
   const typename DATASET_DESCRIPTOR_T::DATA_T* const queries_ptr,  // [num_queries, dataset_dim]
   const typename DATASET_DESCRIPTOR_T::INDEX_T* const knn_graph,   // [dataset_size, graph_degree]
+  const uint32_t max_elements,
   const uint32_t graph_degree,
   const SourceIndexT* source_indices_ptr,  // [num_queries, search_width]
   const unsigned num_distilation,
@@ -211,7 +233,7 @@ RAFT_KERNEL __launch_bounds__(1024, 1) search_kernel(
   // |<---        result_buffer_size_32                 --->|
   const auto result_buffer_size    = itopk_size + graph_degree;
   const auto result_buffer_size_32 = raft::round_up_safe<uint32_t>(result_buffer_size, 32);
-  assert(result_buffer_size_32 <= MAX_ELEMENTS);
+  assert(result_buffer_size_32 <= max_elements);
 
   // Set smem working buffer for the distance calculation
   dataset_desc = dataset_desc->setup_workspace(smem, queries_ptr, query_id);
@@ -268,8 +290,33 @@ RAFT_KERNEL __launch_bounds__(1024, 1) search_kernel(
     _CLK_START();
     if (threadIdx.x < 32) {
       // [1st warp] Topk with bitonic sort
-      topk_by_bitonic_sort<MAX_ELEMENTS, INDEX_T>(
-        result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+      if constexpr (std::is_same_v<INDEX_T, uint32_t>) {
+        // use a non-template wrapper function to avoid pre-inlining the topk_by_bitonic_sort
+        // function (vs post-inlining, this impacts register pressure)
+        if (max_elements <= 64) {
+          topk_by_bitonic_sort_wrapper_64(
+            result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+        } else if (max_elements <= 128) {
+          topk_by_bitonic_sort_wrapper_128(
+            result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+        } else {
+          assert(max_elements <= 256);
+          topk_by_bitonic_sort_wrapper_256(
+            result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+        }
+      } else {
+        if (max_elements <= 64) {
+          topk_by_bitonic_sort<64, INDEX_T>(
+            result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+        } else if (max_elements <= 128) {
+          topk_by_bitonic_sort<128, INDEX_T>(
+            result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+        } else {
+          assert(max_elements <= 256);
+          topk_by_bitonic_sort<256, INDEX_T>(
+            result_distances_buffer, result_indices_buffer, result_buffer_size_32);
+        }
+      }
     }
     __syncthreads();
     _CLK_REC(clk_topk);
@@ -487,17 +534,12 @@ struct search_kernel_config {
   // Search kernel function type. Note that the actual values for the template value
   // parameters do not matter, because they are not part of the function signature. The
   // second to fourth value parameters will be selected by the choose_* functions below.
-  using kernel_t =
-    decltype(&search_kernel<128, DATASET_DESCRIPTOR_T, SourceIndexT, SAMPLE_FILTER_T>);
+  using kernel_t = decltype(&search_kernel<DATASET_DESCRIPTOR_T, SourceIndexT, SAMPLE_FILTER_T>);
 
   static auto choose_buffer_size(unsigned result_buffer_size, unsigned block_size) -> kernel_t
   {
-    if (result_buffer_size <= 64) {
-      return search_kernel<64, DATASET_DESCRIPTOR_T, SourceIndexT, SAMPLE_FILTER_T>;
-    } else if (result_buffer_size <= 128) {
-      return search_kernel<128, DATASET_DESCRIPTOR_T, SourceIndexT, SAMPLE_FILTER_T>;
-    } else if (result_buffer_size <= 256) {
-      return search_kernel<256, DATASET_DESCRIPTOR_T, SourceIndexT, SAMPLE_FILTER_T>;
+    if (result_buffer_size <= 256) {
+      return search_kernel<DATASET_DESCRIPTOR_T, SourceIndexT, SAMPLE_FILTER_T>;
     }
     THROW("Result buffer size %u larger than max buffer size %u", result_buffer_size, 256);
   }
@@ -536,6 +578,17 @@ void select_and_run(const dataset_descriptor_host<DataT, IndexT, DistanceT>& dat
                          SourceIndexT,
                          SampleFilterT>::choose_buffer_size(result_buffer_size, block_size);
 
+  uint32_t max_elements{};
+  if (result_buffer_size <= 64) {
+    max_elements = 64;
+  } else if (result_buffer_size <= 128) {
+    max_elements = 128;
+  } else if (result_buffer_size <= 256) {
+    max_elements = 256;
+  } else {
+    THROW("Result buffer size %u larger than max buffer size %u", result_buffer_size, 256);
+  }
+
   RAFT_CUDA_TRY(
     cudaFuncSetAttribute(kernel, cudaFuncAttributeMaxDynamicSharedMemorySize, smem_size));
   // Initialize hash table
@@ -560,6 +613,7 @@ void select_and_run(const dataset_descriptor_host<DataT, IndexT, DistanceT>& dat
                                                        dataset_desc.dev_ptr(stream),
                                                        queries_ptr,
                                                        graph.data_handle(),
+                                                       max_elements,
                                                        graph.extent(1),
                                                        source_indices_ptr,
                                                        ps.num_random_samplings,

cpp/src/neighbors/detail/cagra/search_plan.cuh

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2023-2025, NVIDIA CORPORATION.
+ * SPDX-FileCopyrightText: Copyright (c) 2023-2026, NVIDIA CORPORATION.
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -10,7 +10,6 @@
 #include "compute_distance-ext.cuh"
 #include <cuvs/neighbors/common.hpp>
 #include <raft/core/resource/cuda_stream.hpp>
-// #include "search_single_cta_inst.cuh"
 // #include "topk_for_cagra/topk.h"
 
 #include <raft/core/device_mdspan.hpp>

cpp/src/neighbors/detail/cagra/search_single_cta.cuh

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2023-2025, NVIDIA CORPORATION.
+ * SPDX-FileCopyrightText: Copyright (c) 2023-2026, NVIDIA CORPORATION.
  * SPDX-License-Identifier: Apache-2.0
  */
 #pragma once
@@ -117,7 +117,7 @@ struct search
     //
     // Determine the thread block size
     //
-    constexpr unsigned min_block_size       = 64;  // 32 or 64
+    constexpr unsigned min_block_size       = 64;
     constexpr unsigned min_block_size_radix = 256;
     constexpr unsigned max_block_size       = 1024;
     //
@@ -129,13 +129,17 @@ struct search
       sizeof(std::uint32_t) * topk_ws_size + sizeof(std::uint32_t);
 
     std::uint32_t additional_smem_size = 0;
-    if (num_itopk_candidates > 256) {
-      // Tentatively calculate the required share memory size when radix
-      // sort based topk is used, assuming the block size is the maximum.
+    if (num_itopk_candidates > 256) {  // radix sort
+      // Tentatively calculate the required shared memory size when radix sort based topk is used,
+      // assuming the block size is the maximum.
       if (itopk_size <= 256) {
-        additional_smem_size += topk_by_radix_sort<256, INDEX_T>::smem_size * sizeof(std::uint32_t);
+        constexpr unsigned MAX_ITOPK = 256;
+        additional_smem_size +=
+          topk_by_radix_sort<INDEX_T>::smem_size(MAX_ITOPK) * sizeof(std::uint32_t);
       } else {
-        additional_smem_size += topk_by_radix_sort<512, INDEX_T>::smem_size * sizeof(std::uint32_t);
+        constexpr unsigned MAX_ITOPK = 512;
+        additional_smem_size +=
+          topk_by_radix_sort<INDEX_T>::smem_size(MAX_ITOPK) * sizeof(std::uint32_t);
       }
     }
 
@@ -152,7 +156,7 @@ struct search
     if (block_size == 0) {
       block_size = min_block_size;
 
-      if (num_itopk_candidates > 256) {
+      if (num_itopk_candidates > 256) {  // radix sort
         // radix-based topk is used.
         block_size = min_block_size_radix;
 
@@ -190,19 +194,6 @@ struct search
                  max_block_size);
     thread_block_size = block_size;
 
-    if (num_itopk_candidates <= 256) {
-      RAFT_LOG_DEBUG("# bitonic-sort based topk routine is used");
-    } else {
-      RAFT_LOG_DEBUG("# radix-sort based topk routine is used");
-      smem_size = base_smem_size;
-      if (itopk_size <= 256) {
-        constexpr unsigned MAX_ITOPK = 256;
-        smem_size += topk_by_radix_sort<MAX_ITOPK, INDEX_T>::smem_size * sizeof(std::uint32_t);
-      } else {
-        constexpr unsigned MAX_ITOPK = 512;
-        smem_size += topk_by_radix_sort<MAX_ITOPK, INDEX_T>::smem_size * sizeof(std::uint32_t);
-      }
-    }
     RAFT_LOG_DEBUG("# smem_size: %u", smem_size);
     hashmap_size = 0;
     if (small_hash_bitlen == 0 && !this->persistent) {