From a7d17af5141aa8640cfbae3ac7fe0c176d9664ba Mon Sep 17 00:00:00 2001
From: Felix Schlepper <felix.schlepper@cern.ch>
Date: Wed, 27 Aug 2025 10:31:49 +0200
Subject: [PATCH] ITS: skip processing entirely if no clusters/rofs in TF

Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>
---
 .../ITS/tracking/src/TrackingInterface.cxx    | 25 +++++++++++--------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/Detectors/ITSMFT/ITS/tracking/src/TrackingInterface.cxx b/Detectors/ITSMFT/ITS/tracking/src/TrackingInterface.cxx
index d6ac3b5229509..f673d8f446350 100644
--- a/Detectors/ITSMFT/ITS/tracking/src/TrackingInterface.cxx
+++ b/Detectors/ITSMFT/ITS/tracking/src/TrackingInterface.cxx
@@ -99,7 +99,7 @@ void ITSTrackingInterface::run(framework::ProcessingContext& pc)
   irFrames.reserve(trackROFvec.size());
   int nBCPerTF = alpParams.roFrameLengthInBC;
 
-  LOGP(info, "ITSTracker pulled {} clusters, {} RO frames", compClusters.size(), trackROFvec.size());
+  LOGP(info, "ITSTracker pulled {} clusters, {} RO frames {}", compClusters.size(), trackROFvec.size(), compClusters.empty() ? " -> received no processable data will skip" : "");
   const dataformats::MCTruthContainer<MCCompLabel>* labels = nullptr;
   gsl::span<itsmft::MC2ROFRecord const> mc2rofs;
   if (mIsMC) {
@@ -157,7 +157,9 @@ void ITSTrackingInterface::run(framework::ProcessingContext& pc)
   if (mRunVertexer) {
     vertROFvec.reserve(trackROFvec.size());
     // Run seeding vertexer
-    vertexerElapsedTime = mVertexer->clustersToVertices(logger);
+    if (!compClusters.empty()) {
+      vertexerElapsedTime = mVertexer->clustersToVertices(logger);
+    }
   } else { // cosmics
     mTimeFrame->resetRofPV();
   }
@@ -226,7 +228,7 @@ void ITSTrackingInterface::run(framework::ProcessingContext& pc)
       mTimeFrame->addPrimaryVertices(vtxVecLoc, 0);
     }
   }
-  if (mRunVertexer) {
+  if (mRunVertexer && !compClusters.empty()) {
     LOG(info) << fmt::format(" - Vertex seeding total elapsed time: {} ms for {} ({} + {}) vertices found in {}/{} ROFs",
                              vertexerElapsedTime,
                              mTimeFrame->getPrimaryVerticesNum(),
@@ -244,14 +246,15 @@ void ITSTrackingInterface::run(framework::ProcessingContext& pc)
   if (mCosmicsProcessing && compClusters.size() > 1500 * trackROFspan.size()) {
     LOG(error) << "Cosmics processing was requested with an average detector occupancy exceeding 1.e-7, skipping TF processing.";
   } else {
-
-    mTimeFrame->setMultiplicityCutMask(processingMask);
-    mTimeFrame->setROFMask(processUPCMask);
-    // Run CA tracker
-    if (mMode == o2::its::TrackingMode::Async && o2::its::TrackerParamConfig::Instance().fataliseUponFailure) {
-      mTracker->clustersToTracks(logger, fatalLogger);
-    } else {
-      mTracker->clustersToTracks(logger, errorLogger);
+    if (!compClusters.empty()) {
+      mTimeFrame->setMultiplicityCutMask(processingMask);
+      mTimeFrame->setROFMask(processUPCMask);
+      // Run CA tracker
+      if (mMode == o2::its::TrackingMode::Async && o2::its::TrackerParamConfig::Instance().fataliseUponFailure) {
+        mTracker->clustersToTracks(logger, fatalLogger);
+      } else {
+        mTracker->clustersToTracks(logger, errorLogger);
+      }
     }
     size_t totTracks{mTimeFrame->getNumberOfTracks()}, totClusIDs{mTimeFrame->getNumberOfUsedClusters()};
     if (totTracks) {