Get GenXSecAnalyzer in CMSSW: https://twiki.cern.ch/twiki/bin/view/CMS/HowToGenXSecAnalyzer

Calculate the cross section and filter efficiency for a given CMS sample with GenXSecAnalyzer by passing a few root files of this sample:

cmsRun ana.py inputFiles="/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/0256D125-5A44-E811-8C69-44A842CFD64D.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/4EBE7EE6-6444-E811-8AC0-B499BAAC0626.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/38E00F78-7244-E811-9E78-484D7E8DF092.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/C881E0EB-4244-E811-87CB-A4BF0112BE0E.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/7AAF1A9C-4644-E811-A6F7-A4BF0112BE0E.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/BE82E948-4544-E811-A6E0-A4BF0112BE02.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/B2F4F697-4644-E811-822F-A4BF0112BE28.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/28214488-4844-E811-ABE4-001E67E6F805.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/DEA74370-4744-E811-B043-001E677924BA.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/AED9AF8D-4844-E811-909F-001E6779283A.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/DA9DDE4B-4844-E811-8701-A4BF01125B58.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/809FF793-4944-E811-ABD2-001E67E713B3.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/5A654315-4B44-E811-A1C5-001E6779283A.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/DA6C0A21-4B44-E811-BD40-A4BF0108B34A.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/FC493871-4B44-E811-A54F-A4BF0112BE02.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/E63B595F-4C44-E811-9B73-A4BF01125718.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/F23BC775-4D44-E811-96AD-001E6779283A.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/72C3D568-4E44-E811-9FAA-001E6779281E.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/2C75B35B-4E44-E811-96DC-A4BF0112BE02.root,/store/mc/RunIIFall17MiniAODv2/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/MINIAODSIM/PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/70000/D2C06262-5144-E811-8384-A4BF01125718.root"

The output is given here. More examples here.

You can get the list of available root files for a given sample in DAS with the dasgoclient, e.g.:

dasgoclient -query="file dataset=/DYJetsToLL_M-50_TuneCP5_13TeV-madgraphMLM-pythia8/RunIIFall17MiniAODv2-PU2017RECOSIMstep_12Apr2018_94X_mc2017_realistic_v14-v1/MINIAODSIM"