Clarified non-use of CPU platform for BB relaxer

modelling/src/backbone_relaxer.cc

@@ -314,6 +314,8 @@ Real BackboneRelaxer::Run(loop::BackboneList& bb_list, int steps,
 }
 
 void BackboneRelaxer::Init() {
+  core::ScopedTimerPtr prof = core::StaticRuntimeProfiler::StartScoped(
+                                "BackboneRelaxer::Init", 2);
 
   ost::mol::EntityHandle dummy_ent = ost::mol::CreateEntity();
   ost::mol::XCSEditor ed = dummy_ent.EditXCS(ost::mol::BUFFERED_EDIT);
@@ -336,6 +338,14 @@ void BackboneRelaxer::Init() {
     settings->nonbonded_method = ost::mol::mm::CutoffNonPeriodic;
     settings->nonbonded_cutoff = nonbonded_cutoff_;
   }
+  // NOTE: for OpenMM 6.1 and 7.1.1, using CPU is slower so we don't do this...
+  // settings->platform = ost::mol::mm::CPU;
+  // if (ost::mol::mm::Simulation::IsPlatformAvailable(settings)) {
+  //   settings->cpu_properties["CpuThreads"] = "1";
+  // } else {
+  //   // fallback to reference
+  //   settings->platform = ost::mol::mm::Reference;
+  // }
 
   simulation_ = ost::mol::mm::SimulationPtr(
                   new ost::mol::mm::Simulation(top_, dummy_ent, settings));