[SYCL] Add sampling initialization (#10216)

---------

Co-authored-by: Dmitry Razdoburdin <>

tests/ci_build/conda_env/linux_sycl_test.yml

@@ -18,3 +18,4 @@ dependencies:
 - pytest-timeout
 - pytest-cov
 - dpcpp_linux-64
+- onedpl-devel

tests/cpp/plugin/test_sycl_hist_updater.cc

@@ -0,0 +1,104 @@
+/**
+ * Copyright 2020-2024 by XGBoost contributors
+ */
+#include <gtest/gtest.h>
+
+#include <oneapi/dpl/random>
+
+#include "../../../plugin/sycl/tree/hist_updater.h"
+#include "../../../plugin/sycl/device_manager.h"
+
+#include "../helpers.h"
+
+namespace xgboost::sycl::tree {
+
+template <typename GradientSumT>
+class TestHistUpdater : public HistUpdater<GradientSumT> {
+ public:
+  TestHistUpdater(::sycl::queue qu,
+                  const xgboost::tree::TrainParam& param,
+                  std::unique_ptr<TreeUpdater> pruner,
+                  FeatureInteractionConstraintHost int_constraints_,
+                  DMatrix const* fmat) : HistUpdater<GradientSumT>(qu, param, std::move(pruner),
+                                                                   int_constraints_, fmat) {}
+
+  void TestInitSampling(const USMVector<GradientPair, MemoryType::on_device> &gpair,
+                    USMVector<size_t, MemoryType::on_device>* row_indices) {
+    HistUpdater<GradientSumT>::InitSampling(gpair, row_indices);
+  }
+};
+
+template <typename GradientSumT>
+void TestHistUpdaterSampling(const xgboost::tree::TrainParam& param) {
+  const size_t num_rows = 1u << 12;
+  const size_t num_columns = 1;
+
+  Context ctx;
+  ctx.UpdateAllowUnknown(Args{{"device", "sycl"}});
+
+  DeviceManager device_manager;
+  auto qu = device_manager.GetQueue(ctx.Device());
+  ObjInfo task{ObjInfo::kRegression};
+
+  auto p_fmat = RandomDataGenerator{num_rows, num_columns, 0.0}.GenerateDMatrix();
+
+  FeatureInteractionConstraintHost int_constraints;
+  std::unique_ptr<TreeUpdater> pruner{TreeUpdater::Create("prune", &ctx, &task)};
+
+  TestHistUpdater<GradientSumT> updater(qu, param, std::move(pruner), int_constraints, p_fmat.get());
+
+  USMVector<size_t, MemoryType::on_device> row_indices_0(&qu, num_rows);
+  USMVector<size_t, MemoryType::on_device> row_indices_1(&qu, num_rows);
+  USMVector<GradientPair, MemoryType::on_device> gpair(&qu, num_rows);
+  auto* gpair_ptr = gpair.Data();
+  qu.submit([&](::sycl::handler& cgh) {
+    cgh.parallel_for<>(::sycl::range<1>(::sycl::range<1>(num_rows)),
+                                        [=](::sycl::item<1> pid) {
+      uint64_t i = pid.get_linear_id();
+
+      constexpr uint32_t seed = 777;
+      oneapi::dpl::minstd_rand engine(seed, i);
+      oneapi::dpl::uniform_real_distribution<GradientPair::ValueT> distr(-1., 1.);
+      gpair_ptr[i] = {distr(engine), distr(engine)};
+    });
+  }).wait();
+
+  updater.TestInitSampling(gpair, &row_indices_0);
+  
+  size_t n_samples = row_indices_0.Size();
+  // Half of gpairs have neg hess
+  ASSERT_LT(n_samples, num_rows * 0.5 * param.subsample * 1.2);
+  ASSERT_GT(n_samples, num_rows * 0.5 * param.subsample / 1.2);
+
+  // Check if two lanunches generate different realisations:
+  updater.TestInitSampling(gpair, &row_indices_1);
+  if (row_indices_1.Size() == n_samples) {
+    std::vector<size_t> row_indices_0_host(n_samples);
+    std::vector<size_t> row_indices_1_host(n_samples);
+    qu.memcpy(row_indices_0_host.data(), row_indices_0.Data(), n_samples * sizeof(size_t)).wait();
+    qu.memcpy(row_indices_1_host.data(), row_indices_1.Data(), n_samples * sizeof(size_t)).wait();
+
+    // The order in row_indices_0 and row_indices_1 can be different
+    std::set<size_t> rows;
+    for (auto row : row_indices_0_host) {
+      rows.insert(row);
+    }
+
+    size_t num_diffs = 0;
+    for (auto row : row_indices_1_host) {
+      if (rows.count(row) == 0) num_diffs++;
+    }
+
+    ASSERT_NE(num_diffs, 0);
+  }
+
+}
+
+TEST(SyclHistUpdater, Sampling) {
+  xgboost::tree::TrainParam param;
+  param.UpdateAllowUnknown(Args{{"subsample", "0.7"}});
+
+  TestHistUpdaterSampling<float>(param);
+  TestHistUpdaterSampling<double>(param);
+}
+}  // namespace xgboost::sycl::tree