Support column split with GPU quantile (#9370)

src/common/hist_util.cu

@@ -352,7 +352,7 @@ HistogramCuts DeviceSketch(int device, DMatrix* dmat, int max_bins,
       }
     }
   }
-  sketch_container.MakeCuts(&cuts);
+  sketch_container.MakeCuts(&cuts, dmat->Info().IsColumnSplit());
   return cuts;
 }
 }  // namespace common

src/common/quantile.cu

@@ -501,10 +501,10 @@ void SketchContainer::FixError() {
   });
 }
 
-void SketchContainer::AllReduce() {
+void SketchContainer::AllReduce(bool is_column_split) {
   dh::safe_cuda(cudaSetDevice(device_));
   auto world = collective::GetWorldSize();
-  if (world == 1) {
+  if (world == 1 || is_column_split) {
     return;
   }
 
@@ -582,13 +582,13 @@ struct InvalidCatOp {
 };
 }  // anonymous namespace
 
-void SketchContainer::MakeCuts(HistogramCuts* p_cuts) {
+void SketchContainer::MakeCuts(HistogramCuts* p_cuts, bool is_column_split) {
   timer_.Start(__func__);
   dh::safe_cuda(cudaSetDevice(device_));
   p_cuts->min_vals_.Resize(num_columns_);
 
   // Sync between workers.
-  this->AllReduce();
+  this->AllReduce(is_column_split);
 
   // Prune to final number of bins.
   this->Prune(num_bins_ + 1);

src/common/quantile.cuh

@@ -154,9 +154,9 @@ class SketchContainer {
              Span<SketchEntry const> that);
 
   /* \brief Merge quantiles from other GPU workers. */
-  void AllReduce();
+  void AllReduce(bool is_column_split);
   /* \brief Create the final histogram cut values. */
-  void MakeCuts(HistogramCuts* cuts);
+  void MakeCuts(HistogramCuts* cuts, bool is_column_split);
 
   Span<SketchEntry const> Data() const {
     return {this->Current().data().get(), this->Current().size()};