Integrate KNN implementation: ivf-flat

cpp/bench/CMakeLists.txt

@@ -30,6 +30,7 @@ add_executable(${RAFT_CPP_BENCH_TARGET}
   bench/random/permute.cu
   bench/random/rng.cu
   bench/spatial/fused_l2_nn.cu
+  bench/spatial/knn.cu
   bench/spatial/selection.cu
   bench/main.cpp
 )

cpp/bench/common/benchmark.hpp

@@ -122,6 +122,13 @@ class fixture {
   virtual void run_benchmark(::benchmark::State& state) = 0;
   virtual void generate_metrics(::benchmark::State& state) {}
 
+ protected:
+  /** The helper that writes zeroes to some buffer in GPU memory to flush the L2 cache.  */
+  void flush_L2_cache()
+  {
+    RAFT_CUDA_TRY(cudaMemsetAsync(scratch_buf_.data(), 0, scratch_buf_.size(), stream));
+  }
+
   /**
    * The helper to be used inside `run_benchmark`, to loop over the state and record time using the
    * cuda_event_timer.
@@ -130,9 +137,7 @@ class fixture {
   void loop_on_state(::benchmark::State& state, Lambda benchmark_func, bool flush_L2 = true)
   {
     for (auto _ : state) {
-      if (flush_L2) {
-        RAFT_CUDA_TRY(cudaMemsetAsync(scratch_buf_.data(), 0, scratch_buf_.size(), stream));
-      }
+      if (flush_L2) { flush_L2_cache(); }
       cuda_event_timer timer(state, stream);
       benchmark_func();
     }
@@ -147,9 +152,9 @@ class Fixture : public ::benchmark::Fixture {
 
  public:
   explicit Fixture(const std::string name, const Params&... params)
-    : ::benchmark::Fixture(), params_(params...)
+    : ::benchmark::Fixture(), params_(params...), name_(name)
   {
-    SetName(name.c_str());
+    SetName(name_.c_str());
   }
   Fixture() = delete;
 
@@ -165,6 +170,7 @@ class Fixture : public ::benchmark::Fixture {
  private:
   std::unique_ptr<Class> fixture_;
   std::tuple<Params...> params_;
+  const std::string name_;
 
  protected:
   void BenchmarkCase(State& state) override