Flows: fix bottleneck from refiner construction

Author: N-Maas

mt-kahypar/partition/refinement/flows/flow_refinement_scheduler.cpp

@@ -219,6 +219,10 @@ HyperedgeWeight FlowRefinementScheduler<GraphAndGainTypes>::runFlowSearch(Partit
   auto start = std::chrono::high_resolution_clock::now();
   if ( sub_hg.numNodes() > 0 ) {
     auto partitioned_hg = utils::partitioned_hg_const_cast(phg);
+
+    if (_refiner[refiner_idx] == nullptr) {
+      _refiner[refiner_idx] = constructFlowRefiner();
+    }
     _refiner[refiner_idx]->initialize(partitioned_hg);
     _refiner[refiner_idx]->updateTimeLimit(time_limit);
     MoveSequence sequence = _refiner[refiner_idx]->refine(partitioned_hg, sub_hg, start);
@@ -366,13 +370,6 @@ void FlowRefinementScheduler<GraphAndGainTypes>::initializeImpl(mt_kahypar_parti
       phg.partWeight(i), _context.partition.max_part_weights[i]);
   }
 
-  // Initialize Refiners
-  for (auto& refiner: _refiner) {
-    if ( refiner == nullptr ) {
-      refiner = constructFlowRefiner();
-    }
-  }
-
   // Initialize Quotient Graph and Scheduler
   _stats.reset();
   utils::Timer& timer = utils::Utilities::instance().getTimer(_context.utility_id);

mt-kahypar/partition/refinement/flows/flow_refiner.cpp

@@ -157,10 +157,18 @@ FlowProblem FlowRefiner<GraphAndGainTypes>::constructFlowHypergraph(const Partit
 
   const bool sequential = _context.shared_memory.num_threads == _context.refinement.flows.num_parallel_searches;
   if ( sequential ) {
-    flow_problem = _sequential_construction.constructFlowHypergraph(
+    if ( _sequential_construction == nullptr ) {
+      _sequential_construction = std::make_unique<SequentialConstruction<GraphAndGainTypes>>(
+        _num_hyperedges, _flow_hg, _sequential_hfc, _context);
+    }
+    flow_problem = _sequential_construction->constructFlowHypergraph(
       phg, sub_hg, _block_0, _block_1, _whfc_to_node);
   } else {
-    flow_problem = _parallel_construction.constructFlowHypergraph(
+    if ( _parallel_construction == nullptr ) {
+      _parallel_construction = std::make_unique<ParallelConstruction<GraphAndGainTypes>>(
+        _num_hyperedges, _flow_hg, _parallel_hfc, _context);
+    }
+    flow_problem = _parallel_construction->constructFlowHypergraph(
       phg, sub_hg, _block_0, _block_1, _whfc_to_node);
   }
 

mt-kahypar/partition/refinement/flows/flow_refiner.h

@@ -27,6 +27,8 @@
 
 #pragma once
 
+#include <memory>
+
 #include <tbb/concurrent_vector.h>
 
 #include "WHFC/algorithm/hyperflowcutter.h"
@@ -57,14 +59,15 @@ class FlowRefiner final : public IFlowRefiner {
                        const Context& context) :
     _phg(nullptr),
     _context(context),
+    _num_hyperedges(num_hyperedges),
     _block_0(kInvalidPartition),
     _block_1(kInvalidPartition),
     _flow_hg(),
     _sequential_hfc(_flow_hg, context.partition.seed),
     _parallel_hfc(_flow_hg, context.partition.seed),
     _whfc_to_node(),
-    _sequential_construction(num_hyperedges, _flow_hg, _sequential_hfc, context),
-    _parallel_construction(num_hyperedges, _flow_hg, _parallel_hfc, context) {
+    _sequential_construction(nullptr),
+    _parallel_construction(nullptr) {
       _sequential_hfc.find_most_balanced = _context.refinement.flows.find_most_balanced_cut;
       _sequential_hfc.timer.active = false;
       _sequential_hfc.forceSequential(true);
@@ -111,14 +114,15 @@ class FlowRefiner final : public IFlowRefiner {
   const Context& _context;
   using IFlowRefiner::_time_limit;
 
+  HyperedgeID _num_hyperedges;
   PartitionID _block_0;
   PartitionID _block_1;
   FlowHypergraphBuilder _flow_hg;
   whfc::HyperFlowCutter<whfc::SequentialPushRelabel> _sequential_hfc;
   whfc::HyperFlowCutter<whfc::ParallelPushRelabel> _parallel_hfc;
 
   vec<HypernodeID> _whfc_to_node;
-  SequentialConstruction<GraphAndGainTypes> _sequential_construction;
-  ParallelConstruction<GraphAndGainTypes> _parallel_construction;
+  std::unique_ptr<SequentialConstruction<GraphAndGainTypes>> _sequential_construction;
+  std::unique_ptr<ParallelConstruction<GraphAndGainTypes>> _parallel_construction;
 };
 }  // namespace mt_kahypar