diff --git a/include/xgboost/collective/socket.h b/include/xgboost/collective/socket.h
index c5dd977f6255..84885cf317f5 100644
--- a/include/xgboost/collective/socket.h
+++ b/include/xgboost/collective/socket.h
@@ -548,13 +548,10 @@ class TCPSocket {
   [[nodiscard]] HandleT const &Handle() const { return handle_; }
   /**
    * @brief Listen to incoming requests. Should be called after bind.
+   *
+   *   Both the default and minimum backlog is set to 256.
    */
-  [[nodiscard]] Result Listen(std::int32_t backlog = 16) {
-    if (listen(handle_, backlog) != 0) {
-      return system::FailWithCode("Failed to listen.");
-    }
-    return Success();
-  }
+  [[nodiscard]] Result Listen(std::int32_t backlog = 256);
   /**
    * @brief Bind socket to INADDR_ANY, return the port selected by the OS.
    */
diff --git a/src/collective/socket.cc b/src/collective/socket.cc
index 5145c13a1366..dd6c05e6f964 100644
--- a/src/collective/socket.cc
+++ b/src/collective/socket.cc
@@ -3,6 +3,7 @@
  */
 #include "xgboost/collective/socket.h"
 
+#include <algorithm>     // for max
 #include <array>         // for array
 #include <cstddef>       // std::size_t
 #include <cstdint>       // std::int32_t
@@ -58,6 +59,14 @@ SockAddrV4 SockAddrV4::InaddrAny() { return MakeSockAddress("0.0.0.0", 0).V4();
 SockAddrV6 SockAddrV6::Loopback() { return MakeSockAddress("::1", 0).V6(); }
 SockAddrV6 SockAddrV6::InaddrAny() { return MakeSockAddress("::", 0).V6(); }
 
+[[nodiscard]] Result TCPSocket::Listen(std::int32_t backlog) {
+  backlog = std::max(backlog, 256);
+  if (listen(this->handle_, backlog) != 0) {
+    return system::FailWithCode("Failed to listen.");
+  }
+  return Success();
+}
+
 std::size_t TCPSocket::Send(StringView str) {
   CHECK(!this->IsClosed());
   CHECK_LT(str.size(), std::numeric_limits<std::int32_t>::max());
diff --git a/src/collective/tracker.cc b/src/collective/tracker.cc
index c8776f294690..9bffbc5590e5 100644
--- a/src/collective/tracker.cc
+++ b/src/collective/tracker.cc
@@ -120,7 +120,8 @@ RabitTracker::RabitTracker(Json const& config) : Tracker{config} {
     listener_ = TCPSocket::Create(addr.IsV4() ? SockDomain::kV4 : SockDomain::kV6);
     return listener_.Bind(host_, &this->port_);
   } << [&] {
-    return listener_.Listen();
+    CHECK_GT(this->n_workers_, 0);
+    return listener_.Listen(this->n_workers_);
   };
   SafeColl(rc);
 }
diff --git a/src/common/device_helpers.cuh b/src/common/device_helpers.cuh
index f4fce42f84f8..03b8f2c0a40c 100644
--- a/src/common/device_helpers.cuh
+++ b/src/common/device_helpers.cuh
@@ -224,13 +224,6 @@ __global__ void LaunchNKernel(size_t begin, size_t end, L lambda) {
     lambda(i);
   }
 }
-template <typename L>
-__global__ void LaunchNKernel(int device_idx, size_t begin, size_t end,
-                              L lambda) {
-  for (auto i : GridStrideRange(begin, end)) {
-    lambda(i, device_idx);
-  }
-}
 
 /* \brief A wrapper around kernel launching syntax, used to guard against empty input.
  *
diff --git a/src/tree/gpu_hist/row_partitioner.cuh b/src/tree/gpu_hist/row_partitioner.cuh
index fde6c4dd0fa9..cf1f0e4edf6e 100644
--- a/src/tree/gpu_hist/row_partitioner.cuh
+++ b/src/tree/gpu_hist/row_partitioner.cuh
@@ -146,10 +146,11 @@ void SortPositionBatch(common::Span<const PerNodeData<OpDataT>> d_batch_info,
 
   // Value found by experimentation
   const int kItemsThread = 12;
-  const int grid_size = xgboost::common::DivRoundUp(total_rows, kBlockSize * kItemsThread);
 
-  SortPositionCopyKernel<kBlockSize, RowIndexT, OpDataT>
-      <<<grid_size, kBlockSize, 0>>>(batch_info_itr, ridx, ridx_tmp, total_rows);
+  std::uint32_t const kGridSize =
+      xgboost::common::DivRoundUp(total_rows, kBlockSize * kItemsThread);
+  dh::LaunchKernel{kGridSize, kBlockSize, 0}(SortPositionCopyKernel<kBlockSize, RowIndexT, OpDataT>,
+                                             batch_info_itr, ridx, ridx_tmp, total_rows);
 }
 
 struct NodePositionInfo {
@@ -328,11 +329,13 @@ class RowPartitioner {
                                   sizeof(NodePositionInfo) * ridx_segments_.size(),
                                   cudaMemcpyDefault));
 
-    constexpr int kBlockSize = 512;
+    constexpr std::uint32_t kBlockSize = 512;
     const int kItemsThread = 8;
-    const int grid_size = xgboost::common::DivRoundUp(ridx_.size(), kBlockSize * kItemsThread);
+    const std::uint32_t grid_size =
+        xgboost::common::DivRoundUp(ridx_.size(), kBlockSize * kItemsThread);
     common::Span<const RowIndexT> d_ridx(ridx_.data().get(), ridx_.size());
-    FinalisePositionKernel<kBlockSize><<<grid_size, kBlockSize, 0>>>(
+    dh::LaunchKernel{grid_size, kBlockSize}(
+        FinalisePositionKernel<kBlockSize, RowIndexT, FinalisePositionOpT>,
         dh::ToSpan(d_node_info_storage), d_ridx, d_out_position, op);
   }
 };
diff --git a/tests/cpp/tree/gpu_hist/test_row_partitioner.cu b/tests/cpp/tree/gpu_hist/test_row_partitioner.cu
index 14ea6fd70a4e..54bf17247432 100644
--- a/tests/cpp/tree/gpu_hist/test_row_partitioner.cu
+++ b/tests/cpp/tree/gpu_hist/test_row_partitioner.cu
@@ -6,15 +6,12 @@
 #include <thrust/host_vector.h>
 #include <thrust/sequence.h>
 
-#include <algorithm>
 #include <vector>
 
 #include "../../../../src/tree/gpu_hist/row_partitioner.cuh"
 #include "../../helpers.h"
 #include "xgboost/base.h"
-#include "xgboost/context.h"
-#include "xgboost/task.h"
-#include "xgboost/tree_model.h"
+#include "../../helpers.h"                 // for RandomDataGenerator
 
 namespace xgboost::tree {
 void TestUpdatePositionBatch() {
@@ -55,7 +52,9 @@ void TestSortPositionBatch(const std::vector<int>& ridx_in, const std::vector<Se
   thrust::device_vector<uint32_t> ridx_tmp(ridx_in.size());
   thrust::device_vector<bst_uint> counts(segments.size());
 
-  auto op = [=] __device__(auto ridx, int split_index, int data) { return ridx % 2 == 0; };
+  auto op = [=] __device__(auto ridx, int split_index, int data) {
+    return ridx % 2 == 0;
+  };
   std::vector<int> op_data(segments.size());
   std::vector<PerNodeData<int>> h_batch_info(segments.size());
   dh::TemporaryArray<PerNodeData<int>> d_batch_info(segments.size());
@@ -73,7 +72,9 @@ void TestSortPositionBatch(const std::vector<int>& ridx_in, const std::vector<Se
                                                  dh::ToSpan(ridx_tmp), dh::ToSpan(counts),
                                                  total_rows, op, &tmp);
 
-  auto op_without_data = [=] __device__(auto ridx) { return ridx % 2 == 0; };
+  auto op_without_data = [=] __device__(auto ridx) {
+    return ridx % 2 == 0;
+  };
   for (size_t i = 0; i < segments.size(); i++) {
     auto begin = ridx.begin() + segments[i].begin;
     auto end = ridx.begin() + segments[i].end;
@@ -87,11 +88,10 @@ void TestSortPositionBatch(const std::vector<int>& ridx_in, const std::vector<Se
   }
 }
 
-TEST(GpuHist, SortPositionBatch) {
+TEST(RowPartitioner, SortPositionBatch) {
   TestSortPositionBatch({0, 1, 2, 3, 4, 5}, {{0, 3}, {3, 6}});
   TestSortPositionBatch({0, 1, 2, 3, 4, 5}, {{0, 1}, {3, 6}});
   TestSortPositionBatch({0, 1, 2, 3, 4, 5}, {{0, 6}});
   TestSortPositionBatch({0, 1, 2, 3, 4, 5}, {{3, 6}, {0, 2}});
 }
-
 }  // namespace xgboost::tree