Performance of the default node allocator.

[Dhruv Matani]

On Tue, 2003-11-11 at 11:58, Loren James Rittle wrote:
> > I have here a program that allocates lots of list node, deallocates
> > them, and then reallocates them. It appears that the default node
> > allocator fails to preserve the locality or something, and it's
> > performance is reflected while sorting the list, when the 2nd time
is 
> > observered to perform much worse compared to the first (double the
> > time). I wonder if the allocation starategy of the default node
> > allocator can be changed? BTW, an allocator calling malloc and free
> > performs better in terms of preserving order of elements in memory.
> 
> Hi, This is the best answer I can give quickly.
> 
> I think your test is somewhat interesting.  However, the library
> doesn't make performance guarantees regarding interactions with the
> cache architecture on any given platform.  I believe that is the
> effect you are seeing.  Based on your report, I assume that malloc
> implementations which do coalescing and/or ordering upon free() will
> perform better, with your case mapped directly to malloc, than those
> that don't.  Hint: the library does no coalescing or ordering of its
> free list.

Ok. Yes, that's what I was getting at.


> Dhruv, do I have your permission to install this modified version of
> your performance test case?
> 
Yes, sure...


> Regards,
> Loren
> 
> #include <iostream>
> #include <algorithm>
> #include <list>
> #include <memory>
> #include <testsuite_performance.h>
> 
> template <class T>
> void clear_container (T& _cont) { T temp; std::swap (temp, _cont); }
> 
> int main ()
> {
>   std::list <double> il;
>   using namespace __gnu_test;
>   time_counter time;
>   resource_counter resource;
> 
>   for (int x = 3; x--;)
>     {
>       srand(0);
>       start_counters(time, resource);
>       for (int i = 0; i < 700000; ++i)
>       il.push_back(rand()%300);
>       stop_counters(time, resource);
>       report_performance(__FILE__, "insert", time, resource);
> 
>       start_counters(time, resource);
>       il.sort();
>       stop_counters(time, resource);
>       report_performance(__FILE__, "sort", time, resource);
> 
>       start_counters(time, resource);
>       clear_container(il);
>       stop_counters(time, resource);
>       report_performance(__FILE__, "clear", time, resource);
>     }
> }



-- 
	-Dhruv Matani.
http://www.geocities.com/dhruvbird/