Merge branch '22.0.18-OnlinePrescalingBiasInvestigation' into 'master'

Prescaling of the costmon chain

See merge request atlas/athena!37183

Trigger/TrigSteer/L1Decoder/python/L1DecoderMonitoring.py

@@ -34,4 +34,7 @@ def PrescalingMonitoring():
     tool.defineHistogram('LB,HLTPSK', path='EXPERT', type='TH2I', opt='kAddBinsDynamically',
                          title='HLT prescale key used in LB;Lumiblock;HLTPSK',
                          xbins=100, xmin=0, xmax=100, ybins=5, ymin=0, ymax=5)
+    tool.defineHistogram('Random', path='EXPERT', type='TH1F',
+                         title='Random number distribution;random number',
+                         xbins=100, xmin=0, xmax=1)
     return tool

Trigger/TrigSteer/L1Decoder/src/PrescalingTool.cxx

@@ -91,7 +91,12 @@ StatusCode PrescalingTool::prescaleChains( const EventContext& ctx,
       try {
          const auto & prescale = hltPrescaleSet->prescale( ch.numeric() );
          if( prescale.enabled ) {
-            decisionToKeep = engine->flat() < 1./prescale.prescale;
+            auto flat = engine->flat();
+            if(ch.numeric() == 843341480) { // this is to explicitly monitor the chain HLT_costmonitor_CostMonDS_L1All (hash 843341480)
+               auto mon_rndm = Monitored::Scalar<double>("Random", flat);
+               Monitored::Group(m_monTool, mon_rndm);
+            }
+            decisionToKeep = flat < 1./prescale.prescale;
             ATH_MSG_DEBUG("Prescaling decision for chain " << ch << " " << decisionToKeep );
          } else {
             decisionToKeep = false;