Re: [eigen] two things

[Benoît Jacob <jacob@xxxxxxxxxxxxxxx>]

Thanks a lot for the experimental data, very useful!
Benoit

On Wednesday 25 June 2008 22:51:40 Gael Guennebaud wrote:
> ok, so I benched a = a + b, 400x400 (10000 repetitions)
>
> hand coded vector with loop peeling:
> 1.0101 sec 1.47521 GFlops
>
> VectorXf(400*400):
> 1.50368 0.990978 GFlops
>
> MatrixXf, various configuration inner/outer:
> 400 x 400  1.69703s   0.878074 GFlops
> 320 x 500  1.61007s   0.925497 GFlops
> 256 x 625  1.65798s   0.898753 GFlops
> 250 x 640  1.72979s   0.861445 GFlops
> 200 x 800  1.7328s   0.859946 GFlops
> 160 x 1000  1.78083s   0.836755 GFlops
> 128 x 1250  1.70838s   0.872238 GFlops
> 125 x 1280  1.83812s   0.810676 GFlops
> 100 x 1600  1.79399s   0.830616 GFlops
> 80 x 2000  1.90025s   0.78417 GFlops
> 64 x 2500  1.91228s   0.779236 GFlops
> 50 x 3200  2.40844s   0.618706 GFlops
> 40 x 4000  2.08198s   0.715722 GFlops
> 32 x 5000  2.30892s   0.645372 GFlops
> 25 x 6400  3.05263s   0.488142 GFlops
> 20 x 8000  2.89561s   0.514611 GFlops
> 16 x 10000  3.36251s   0.443156 GFlops
> 10 x 16000  6.72561s   0.221559 GFlops
> 8 x 20000  8.03166s   0.18553 GFlops
> 5 x 32000  8.08158s   0.184384 GFlops
> 4 x 40000  9.30723s   0.160103 GFlops
>
> so .... yeah why not !
>
> gael.
>
> On Wed, Jun 25, 2008 at 10:17 PM, Benoît Jacob <jacob@xxxxxxxxxxxxxxx> 
wrote:
> > On Wednesday 25 June 2008 22:09:17 Gael Guennebaud wrote:
> >> right, an intermediate solution would be to specialize Matrix<> if one
> >> of the dim is 1, e.g. let's add an additional "hidden" template
> >> parameter:
> >>
> >> template <typename T, int R, int C, ...,  int IsVector = R==1 || C==1>
> >> class Matrix {....};
> >>
> >> template <typename T, int R, int C, ..., int Flags>
> >> class Matrix<T,R,C, ...,  MaxSize,1,Flags,true> {  /* vector */ };
> >>
> >> but this only allows to improve a bit the constructors and this does
> >> not offer any template Vector<> class, so I'm not sure it's  worth it,
> >> just an idea....
> >
> > It's interesting, I'm not opposed to it; on the other hand like you i'm
> > not sure if it's worth the effort, as the problems with the matrix
> > constructors are essentially "virtual problems" which don't cause harm in
> > practice.
> >
> >> > 2) about linear vectorization: i remember you suggested adding a
> >> > packet(int) method. I think this is still a good idea and would still
> >> > improve linear vectorization despite the improvements you already
> >> > made. OK?
> >>
> >> actually I'm not sure that's worth it: I've done some bench and if I
> >> remember well the overhead between a MatrixXf(R,C); versus a
> >> VectorXf(R*C); was negligible, like x1.1 or x1.2.....
> >
> > so it was a 10% or 20% speed difference? Not what I call negligible!
> >
> > Also, the speed difference becomes bigger as the InnerSize is small. What
> > sizes did you test?
> >
> > Cheers,
> >
> > Benoit

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