Why worse performace in euclidean distance with SSE2?

Dario Bahena Tapia dario.mx@gmail.com
Mon Apr 7 17:02:00 GMT 2008


Hello,

I tried with your options but it seems to make no difference. In
another email it was suggested to use _mm_sqrt_sd, because I only
needed one sqrt calculation. That improved time and indeed, almost
reach serial version (now it runs up to 1 second slower for the 10,000
data example, hehe).

But of course, I would wanna/expect the vector version to run faster
... still unsure how to achieve that.

Thanks

On Mon, Apr 7, 2008 at 10:23 AM, jlh <jlh@gmx.ch> wrote:
> Dario Bahena Tapia wrote:
>
> >
> > inline static double dist(int i,int j)
> > {
> >  double xd = C[i][X] - C[j][X];
> >  double yd = C[i][Y] - C[j][Y];
> >  return rint(sqrt(xd*xd + yd*yd));
> > }
> > [...]
> >
> > And in order to activate the SSE2 features, I am using the following
> > flags for gcc (my computer is a laptop):
> >
> > CFLAGS = -O -Wall -march=pentium-m -msse2
> >
>
>  These options do not make dist() use any SSE for me.  Have you
>  tried compiling with this?
>
>  CFLAGS = -O2 -Wall -march=pentium-m -mfpmath=sse
>
>  I think -msse2 is redundant if you say -march-pentium-m.  I don't
>  have an SSE2 machine to try this though.
>
>  jlh
>



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