Re: performance : TTree::Project vs Loop() from MakeClass() with a Fill() instruction

Instead of
  time -q -x -b TheMacro.C
could you do
  time -q -x -b TheMacro.C+

Rene Brun

Marc Escalier wrote:
> Dear rooters,
>
> i compared performance of filling an histograms in two ways from a
> TChain list of files
>
> 1) using a direct filling using the TTree::Project() method
> 2) using a MakeClass created from a TChain () and filling the
> histogram in a loop on the events
> (of course i deactivated the branchs that are not useful to speed up
> the Loop() )
>
> but from performance (time -q -x -b TheMacro.C)
> i see that the Project() is much faster than the Loop() method of a
> class generated from a MakeClass() instruction
>
> ==>would you know why and how to make the Loop() as fast as the
> Project() method
>
> i see that if i do many Project(), at a given threshold of number of
> histograms to fill, the Loop() method becomes more faster,
> because in the Project() method, one loop each time on the whole
> events while in the Loop() method from MakeClass() filling the
> histograms on the fly, whereas in the Project() method,
> it loops each time again on the events. So my goal would be to
> understand the fact that individual Project() method is so fast, in
> order to improve the Loop() method that is automaticaly generated from
> the MakeClass() instruction (sorry for redundance of the observed
> behaviour, it is to explains the phenomena)
>
> thank you
>
> here is a minimal example :
> {
> #include "PAUReco.C"
>
> TChain *mychain_data_7000=new TChain("PAUReco");
> gROOT->ProcessLine(".x menu_ChooseDatasets.C");
>
> TH1F *hist1=new TH1F("hist1","hist1",1,0,2000);
>
> //first method :
> mychain_data_7000->Project("hist1","ph_pt/1000");
>
> //second method : (i comment the first or the second method to
> compare performances)
> PAUReco myPAUReco(mychain_data_7000);
> myPAUReco.Loop();
> }
>
>
> mychain_data_7000->Add("/sps/atlas/l/lal-photon/Trash/PAU-00-01-73/data_cutPt9/L1Calo/Run152166/*root*");
>
>
> -------------------------------------
> PAUReco.C :
>
> void PAUReco::Loop()
> {
> if (fChain == 0) return;
>
> fChain->SetBranchStatus("*",0);
> fChain->SetBranchStatus("ph_pt",1);
>
> Long64_t nentries = fChain->GetEntries();
>
> for (Long64_t jentry=0; jentry<nentries;jentry++) {
> Long64_t ientry = LoadTree(jentry);
>
> if (ientry < 0) break;
> fChain->GetEntry(jentry); // nbytes += nb;
> int mysize=ph_pt->size();
> for (int i_photon=0;i_photon<mysize;i_photon++) {
> float myph_pt=ph_pt->at(i_photon)/1000.;
>
> hist1->Fill(myph_pt); }
> } //end loop en entries
> }
>
Received on Thu May 20 2010 - 16:27:57 CEST