Re: [Toon-members] Should dynamic really be this slow?

[Gerhard Reitmayr]

Observed the same on my G4 powerbook.

multiplication with dynamic vector (result of slice() ) produced a  
dynamic vector temporary which allocates the data on the heap! the  
profiler shows most time is spend allocating and deleting the data  
store per loop.

a small fix to linoperators.h rectifies this for your example because  
the result size is known for the fixed matrix * dyn vec case. that  
brings it to comparable speed on my machine.

however, combinations really requiring a dynamic temporary are still  
slow. for example change to:
Matrix<> m2(2,2); Identity(m2);

what about a dedicated memory manager for small double arrays ?

Gerhard

On 20 Jun 2007, at 18:35, Georg Klein wrote:

> I was surprised by this:
>
> static.cc:
> #include <TooN/numerics.h>
> #include <TooN/helpers.h>
> int main()
> {
>   Vector<2> v2;  Zero(v2);
>   Matrix<2> m2;  Identity(m2);
>   Vector<3> v3((double[]){1.0,1.0,1.0});
>   for(int i=0; i<100000000; i++)
>       v2 += m2 * v3.slice<0,2>();
>   return v2[0];
> }
>
> compiling with O3 and running this on my machine takes 0.27  
> seconds. Pretty cool.
>
> If however I chance the crunchy line to
> v2 += m2 * v3.slice(0,2);
>
> it takes 4.3 seconds. That's 16 times slower. That's a lot! Can  
> anyone reproduce this? Compiling with -DNDEBUG to get rid of the  
> assert makes hardly any difference.
>
>
>
>
>
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--
Gerhard Reitmayr
MIL, Engineering Department, Cambridge University
http://mi.eng.cam.ac.uk/~gr281/