Re: TH1 and Fill

Hello Marc,

Ok, here's the part that is hard to answer without looking at your code ... when you say

" ... i see that about 90 % of the time consuming is in the Fill part of the program ... "

it means exactly the Fill(...) call ? ... or by "part of the program" you mean a context or a few instructions ?

I think, really, the way to go would be to examine your problem instruction by instruction. I don't know of any tricks to speed up the Fill(...) call apart from not making the argument of Fill a too complex calculation. The Fill should not be taking too much time. So, what I am going to do is to show you how to track down your code instruction by instruction by 'profiling' your code. Here's a nice exercise. (if you already know this, I apologize, I will asume you have not done profiling with valgrind before)

I will use ROOT as an API, meaning that I will provide the main() part of the program. Consider the following code

#include <TROOT.h>
#include <TH1F.h>

#include <iostream>

using namespace std;

int main(){

  TH1F * h1 = new TH1F("h1","h1",100,-3.,3.);

  h1->FillRandom("gaus",1000);   

  cout << "[DONE]" << endl;

  return 0;
}

you can compile like this

g++ histoTest.cpp -g3 -W -Wall -o histoTest `$ROOTSYS/bin/root-config --libs` `$ROOTSYS/bin/root-config --cflags`

test it

./histoTest

now let's profile. Run it like this

valgrind --tool=callgrind ./histoTest

it will run quite slow ... valgrind is some sort of virtual machine, patience. At the end you will get a file called

callgrind.out.XXXX

where XXXX is the pid ... you can open it with

kcachegrind callgrind.out.XXXX

magic's here ;) ! .... In the search box look for "FillRandom", and at the right side select the "callee map" ... you will see what's going on by yourself. FillRandom() is calling Fill() at some point. Check how much time the Fill() function takes ... not much, almost negligible in fact. Fill() is really not very heavy. That's why I tend to think in your code Fill() is not the issue.

let me know if this helps

cheers !

John Idarraga

On Fri, 2010-04-23 at 23:11 +0200, Marc Escalier wrote:
>
> i use a TBenchmark to see the time "global", and the time for the
> "filling of the histogram", and i see that about 90 % of the time
> consuming is in the Fill part of the program
Received on Sat Apr 24 2010 - 03:41:33 CEST