More collective aggregators (#9060)

src/metric/survival_metric.cu

@@ -7,6 +7,7 @@
 
 #include <dmlc/registry.h>
 
+#include <array>
 #include <memory>
 #include <vector>
 
@@ -211,10 +212,8 @@ struct EvalEWiseSurvivalBase : public MetricNoCache {
     auto result = reducer_.Reduce(*ctx_, info.weights_, info.labels_lower_bound_,
                                   info.labels_upper_bound_, preds);
 
-    double dat[2]{result.Residue(), result.Weights()};
-    if (info.IsRowSplit()) {
-      collective::Allreduce<collective::Operation::kSum>(dat, 2);
-    }
+    std::array<double, 2> dat{result.Residue(), result.Weights()};
+    collective::GlobalSum(info, &dat);
     return Policy::GetFinal(dat[0], dat[1]);
   }