Better tie-breaking: favor lower featureID, kLeftDir

dmlc · Sep 15, 2021 · 7b8bf95 · 7b8bf95
1 parent ce86fdc
commit 7b8bf95
Showing 1 changed file with 18 additions and 0 deletions.
diff --git a/src/tree/gpu_hist/evaluate_splits.cu b/src/tree/gpu_hist/evaluate_splits.cu
@@ -68,6 +68,24 @@ void EvaluateSplits(common::Span<DeviceSplitCandidate> out_splits,
       reduce_val, thrust::make_discard_iterator(), out_reduce.data(),
       thrust::equal_to<int>{},
       [param] __device__(DeviceSplitCandidate l, DeviceSplitCandidate r) {
+        if (l.loss_chg == r.loss_chg
+            && l.left_sum.GetHess() >= param.min_child_weight
+            && l.right_sum.GetHess() >= param.min_child_weight
+            && r.left_sum.GetHess() >= param.min_child_weight
+            && r.right_sum.GetHess() >= param.min_child_weight) {
+          // tie-breaking logic
+          // 1. Favor lower feature ID
+          if (l.findex != r.findex) {
+            return (l.findex < r.findex) ? l : r;
+          }
+          // 2. If using same feature ID, favor kLeftDir direction
+          if (l.dir == DefaultDirection::kLeftDir) {
+            return l;
+          }
+          if (r.dir == DefaultDirection::kLeftDir) {
+            return r;
+          }
+        }
         l.Update(r, param);
         return l;
       });