EventPlaneHelper: avoid copying FT0 Geometry on every call

GetPhiFT0 and SumQvectors took o2::ft0::Geometry by value,
causing a full copy (TObject heap allocation + destruction) on
every invocation. SumQvectors is called ~208 times per event,
so this was ~14% of CPU in Q-vector trains.

Additionally, calculateChannelCenter() was called inside
GetPhiFT0 on every channel, recomputing all 208 channel
positions from scratch each time despite the geometry being
constant.

Fix:
- Pass ft0::Geometry by const reference
- Call calculateChannelCenter() once at init time
- Remove the per-call calculateChannelCenter() from GetPhiFT0

Author: ktf

Common/Core/EventPlaneHelper.cxx

@@ -61,7 +61,7 @@ double EventPlaneHelper::GetPhiFV0(int chno, o2::fv0::Geometry* fv0geom)
   return TMath::ATan2(chPos.y + offsetY, chPos.x + offsetX);
 }
 
-double EventPlaneHelper::GetPhiFT0(int chno, o2::ft0::Geometry ft0geom)
+double EventPlaneHelper::GetPhiFT0(int chno, const o2::ft0::Geometry& ft0geom)
 {
   /* Calculate the azimuthal angle in FT0 for the channel number 'chno'. The offset
     of FT0-A is taken into account if chno is between 0 and 95. */
@@ -74,14 +74,12 @@ double EventPlaneHelper::GetPhiFT0(int chno, o2::ft0::Geometry ft0geom)
     offsetY = mOffsetFT0AY;
   }
 
-  ft0geom.calculateChannelCenter();
   auto chPos = ft0geom.getChannelCenter(chno);
-  /// printf("Channel id: %d X: %.3f Y: %.3f\n", chno, chPos.X(), chPos.Y());
 
   return TMath::ATan2(chPos.Y() + offsetY, chPos.X() + offsetX);
 }
 
-void EventPlaneHelper::SumQvectors(int det, int chno, float ampl, int nmod, TComplex& Qvec, float& sum, o2::ft0::Geometry ft0geom, o2::fv0::Geometry* fv0geom)
+void EventPlaneHelper::SumQvectors(int det, int chno, float ampl, int nmod, TComplex& Qvec, float& sum, const o2::ft0::Geometry& ft0geom, o2::fv0::Geometry* fv0geom)
 {
   /* Calculate the complex Q-vector for the provided detector and channel number,
     before adding it to the total Q-vector given as argument. */

Common/Core/EventPlaneHelper.h

@@ -60,12 +60,12 @@ class EventPlaneHelper
   }
 
   // Methods to calculate the azimuthal angles for each part of FIT, given the channel number.
-  double GetPhiFT0(int chno, o2::ft0::Geometry ft0geom);
+  double GetPhiFT0(int chno, const o2::ft0::Geometry& ft0geom);
   double GetPhiFV0(int chno, o2::fv0::Geometry* fv0geom);
 
   // Method to get the Q-vector and sum of amplitudes for any channel in FIT, given
   // the detector and amplitude.
-  void SumQvectors(int det, int chno, float ampl, int nmod, TComplex& Qvec, float& sum, o2::ft0::Geometry ft0geom, o2::fv0::Geometry* fv0geom);
+  void SumQvectors(int det, int chno, float ampl, int nmod, TComplex& Qvec, float& sum, const o2::ft0::Geometry& ft0geom, o2::fv0::Geometry* fv0geom);
 
   // Method to get the bin corresponding to a centrality percentile, according to the
   // centClasses[] array defined in Tasks/qVectorsQA.cxx.

Common/TableProducer/qVectorsTable.cxx

@@ -257,6 +257,7 @@ struct qVectorsTable {
     AxisSpec axisChID = {220, 0, 220};
 
     fv0geom = o2::fv0::Geometry::instance(o2::fv0::Geometry::eUninitialized);
+    ft0geom.calculateChannelCenter();
 
     histosQA.add("ChTracks", "", {HistType::kTHnSparseF, {axisPt, axisEta, axisPhi, axixCent}});
     histosQA.add("FT0Amp", "", {HistType::kTH2F, {axisFITamp, axisChID}});

PWGCF/JCorran/Tasks/jEPFlowAnalysis.cxx

@@ -442,6 +442,7 @@ struct JEPFlowAnalysis {
     ccdb->setCreatedNotAfter(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count());
 
     fv0geom = o2::fv0::Geometry::instance(o2::fv0::Geometry::eUninitialized);
+    ft0geom.calculateChannelCenter();
 
     detId = getdetId(cfgDetName);
     refAId = getdetId(cfgRefAName);