Re: performance of a program with MakeClass vs MakeSelector, and global variable

> I would make that histogram a member of your class, then later when the
> Loop() is finished you return a pointer of that histogram using a public
> member of your class. Another solution is to make that histogram a
> global var. That would be the very easy solution. Either way you will
> be able to compile your code.

thanks John,

indeed, if i make the histogram a member of the class (like i did in the "option 3"

(option 3 :)
>>>> *if now, i put the histogram in "local variables" in the class of the
>>>> Selector (declaration in the header .h and memory allocation in the Begin())
>>>> then the performance of the MakeSelector approach is twice faster as
>>>> compared to the MakeClass approach

then the code will be very fast

actually, the main point is why is it very fast when the variable is local to the class while it is very slow when it is a global variable of the main program that call the instance of the class

On Tue, 6 Jul 2010, John Idarraga wrote:

> Hello Marc,
>
> I would make that histogram a member of your class, then later when the
> Loop() is finished you return a pointer of that histogram using a public
> member of your class. Another solution is to make that histogram a
> global var. That would be the very easy solution. Either way you will
> be able to compile your code.
>
> Another good reason to compile your code. If you are using a lot of
> stdlib stuff ... compiling is highly recommended.
>
> cheers !
>
> John
>
> On Tue, 2010-07-06 at 22:28 +0200, Marc Escalier wrote:
>> thanks John for your suggestions,
>>
>> my problem is that it doesn't compile for the following reason :
>> when compiling, the histogram is unknown to the method of the class :
>>
>> the reason is that :
>>
>> {
>> TH1F *myhisto
>>
>> InstanceOfClass.Loop(*without parameters*)
>> }
>>
>> with :
>> InstanceOfClass.Loop()
>> {
>> work on myhisto that still is accessible "because of the rules of cint"
>> }
>>
>> so it would not compile (i do interpreted code because it is easier to
>> debug and because the gain in speed when compiling is only 10 %. I
>> showed to Rene some time ago that indeed the gain was only 10 % for the
>> specific way of class that i'm using where there is plenty of vectors,
>> which is not optimized for root. But i don't have the choice about the
>> class : it is an "official" format.)
>>
>> thanks
>> ======================
>> On Tue, 6 Jul 2010, John Idarraga wrote:
>>
>>> By the way, before running valgrind --tool=callgrind, compile your macro
>>> with debugging symbols
>>>
>>> 1) if compiling using ACLIC
>>>
>>> .L mystuff.C++g
>>>
>>> 2) if you are compiling by hand you need to pass this flag to g++
>>>
>>> -g3
>>>
>>> cheers,
>>>
>>> John
>>>
>>> On Tue, 2010-07-06 at 19:14 +0200, Marc Escalier wrote:
>>>> Hello,
>>>>
>>>> i observed a strange phenomena with root (i guess it doesn't depend on
>>>> the version, but just in case, it is root 5.22.)
>>>>
>>>> Let's consider a minimum program developped from a MakeClass() and a
>>>> concurrent one with MakeSelector()
>>>> *if the two programs don't fill histogram, i find the same performance
>>>> in time of execution
>>>>
>>>> *if i fill the histogram with a MakeClass approach or a MakeSelector
>>>> approach, for which the histogram has been declared in the main program
>>>> as a global variable
>>>> then the MakeSelector approach is about 10 times slower than the
>>>> MakeClass approach (doing exactly same stuff) (and with desactivation on
>>>> almost all the branches to speed up the process in the two cases)
>>>>
>>>> the program is something like :
>>>>
>>>> {
>>>> Declaration of a histogram
>>>> Call Instance of a Class and loop on it and fill the histogram with
>>>> dummy values
>>>> or
>>>> Call Instance of a Selector and loop on it and fill the histogram with
>>>> dummy values
>>>> }
>>>>
>>>> *if now, i put the histogram in "local variables" in the class of the
>>>> Selector (declaration in the header .h and memory allocation in the Begin())
>>>> then the performance of the MakeSelector approach is twice faster as
>>>> compared to the MakeClass approach
>>>>
>>>> Would you have an idea of the behaviour
>>>>
>>>> thank you very much
>>>>
>>>> just in case you would need more info on the program, it is here (lxplus) :
>>>> /afs/cern.ch/user/e/escalier/public/ForRene
>>>> time root -b -q -x main.C
>>>> to see the differences to apply, you can replace the differences by
>>>> making comment/uncomment of the parts with "option 1", "option 2",
>>>> "option 3"
>>>> (
>>>> "grep option 1" *
>>>> "grep option 2" *
>>>> "grep option 3" *
>>>> )
>>>>
>>>
>>>
>>
>
>
Received on Tue Jul 06 2010 - 22:47:31 CEST