From d0c6a3ba14ecc66174e638c59c86f2a84c8cc0df Mon Sep 17 00:00:00 2001
From: fis <jm.yuan@outlook.com>
Date: Wed, 20 Oct 2021 17:35:00 +0800
Subject: [PATCH 1/2] Avoid omp reduction in rank metric.

---
 src/metric/rank_metric.cc | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/metric/rank_metric.cc b/src/metric/rank_metric.cc
index 193938c0f8e6..470b6cc1aac0 100644
--- a/src/metric/rank_metric.cc
+++ b/src/metric/rank_metric.cc
@@ -192,24 +192,27 @@ struct EvalRank : public Metric, public EvalRankConfig {
       }
     }
 
+    CHECK(tparam_);
+    std::vector<double> sum_tloc(tparam_->Threads(), 0.0);
+
     if (!rank_gpu_ || tparam_->gpu_id < 0) {
       const auto &labels = info.labels_.ConstHostVector();
       const auto &h_preds = preds.ConstHostVector();
 
       dmlc::OMPException exc;
-      #pragma omp parallel reduction(+:sum_metric)
+#pragma omp parallel num_threads(tparam_->Threads())
       {
         exc.Run([&]() {
           // each thread takes a local rec
           PredIndPairContainer rec;
-          #pragma omp for schedule(static)
+#pragma omp for schedule(static)
           for (bst_omp_uint k = 0; k < ngroups; ++k) {
             exc.Run([&]() {
               rec.clear();
               for (unsigned j = gptr[k]; j < gptr[k + 1]; ++j) {
                 rec.emplace_back(h_preds[j], static_cast<int>(labels[j]));
               }
-              sum_metric += this->EvalGroup(&rec);
+              sum_tloc[omp_get_thread_num()] += this->EvalGroup(&rec);
             });
           }
         });
@@ -217,6 +220,8 @@ struct EvalRank : public Metric, public EvalRankConfig {
       exc.Rethrow();
     }
 
+    sum_metric = std::accumulate(sum_tloc.cbegin(), sum_tloc.cend(), 0.0);
+
     if (distributed) {
       bst_float dat[2];
       dat[0] = static_cast<bst_float>(sum_metric);

From 61cbae96d954bc1e851a9f2e11307a64de93d57a Mon Sep 17 00:00:00 2001
From: fis <jm.yuan@outlook.com>
Date: Thu, 21 Oct 2021 13:53:31 +0800
Subject: [PATCH 2/2] Fix.

---
 src/metric/rank_metric.cc | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/metric/rank_metric.cc b/src/metric/rank_metric.cc
index 470b6cc1aac0..797a1d54ac84 100644
--- a/src/metric/rank_metric.cc
+++ b/src/metric/rank_metric.cc
@@ -217,11 +217,10 @@ struct EvalRank : public Metric, public EvalRankConfig {
           }
         });
       }
+      sum_metric = std::accumulate(sum_tloc.cbegin(), sum_tloc.cend(), 0.0);
       exc.Rethrow();
     }
 
-    sum_metric = std::accumulate(sum_tloc.cbegin(), sum_tloc.cend(), 0.0);
-
     if (distributed) {
       bst_float dat[2];
       dat[0] = static_cast<bst_float>(sum_metric);