[CppAD] Preformance Issue during destruction of man ADFun objects

[Brad Bell]

In summary, when doing speed tests with CppAD, it is important to make
sure that the compiler flag NDEBUG is defined; see heading Speed at
      http://www.coin-or.org/CppAD/Doc/faq.xml#Speed


On Tue, 15 Jun 2010, Dominik Skanda wrote:

> Yes I tried it out and it is much faster now!! Thank you very much for
> your help !!! Sure you can put this thread to the mailing list.
>
> regards
> Dominik
>

On Mon, 7 Jun 2010, Dominik Skanda wrote:

> Hello, the reason why I came to the conclusion that it is a problem with 
> CppAD is that If I prevent the CppAD::ADFUN objects from being 
> destructed I don't get any additional delay in the runtime. This is 
> impossible to do with the smart pointer implementation because there the 
> adfun objects get forced to be deleted. I had an implementation without 
> a smartpointer list, but an ordinary pointer list to construct the adfun 
> objects before. I putted the files in the assigned zip file (without 
> atlas_enum.h but makefile is not modified.). If you look at the 
> destructor in the File BDF_integrator.cpp at the lines 1536-1537 , 1619 
> and 1550 this is the place where the CppAD::ADFun Objects gets deleted. 
> By commenting them out the delay in the example vanishes.
> 
> In the example I construct 3 BDF_integrator objects with the first 
> having 586 ADFun objects after taping, the second has 1474 and the last 
> 2732 Objects.
> 
> The f.size_var() is 576 for each adfun object.
> 
> Kind regards
> 
> Dominik
>

I modified you example so that it could be built with or without deleting the 
CppAD tape objects. Below are the results I obtained:
---------------------------------------------------------------------------
DELETE_CPPAD_TAPE = true
Running Time without destruction of integration objects in seconds: 4.75067
Running Time with destruction of integration objects: in seconds: 139.544

DELETE_CPPAD_TAPE = false
Running Time without destruction of integration objects in seconds: 6.72507
Running Time with destruction of integration objects: in seconds: 6.73154
----------------------------------------------------------------------------

This indicates that you are correct in your assessment above. Then I recalled 
that CppAD uses its memory tracking allocator; see
 	http://www.coin-or.org/CppAD/Doc/tracknewdel.xml
and that this tracking can take a long time when a lot of different pieces of 
memory are allocated. Note the discussion of NDEBUG in the documentation for 
the tracking allocator.

I changed the compiler flags for you test case from
 	-g
to
 	-O2 -DNDEBUG
and got the following results:
---------------------------------------------------------------------------
DELETE_CPPAD_TAPE = false
Running Time without destruction of integration objects in seconds: 3.6148
Running Time with destruction of integration objects: in seconds: 3.61623


DELETE_CPPAD_TAPE = true
Running Time without destruction of integration objects in seconds: 4.4784
Running Time with destruction of integration objects: in seconds: 4.75017
----------------------------------------------------------------------------