Re: [eigen] Speed issues, array min,max

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 05.10.2015 19:20, Nate Yonkee wrote:
> Christoph,
>
> You were right about moving the operations outside of main. For long long
> ints the two times are within 1%, even with vectors of length 300. But with
> doubles Eigen is twice as fast at a length of 300; the times are close only
> when I use a tiny length of 3. Do we expect a discrepancy between long
> longs and doubles?

Yes, because doubles are SSE-optimized (if the size is even or Dynamic 
at compile time -- i.e. you might get faster times for 4d than for 3d 
vectors ...)
If you use int32 instead of uint64 you should get a speedup of about 4 
(if the size is a multiple of 4).


Christoph


> On Mon, Oct 5, 2015 at 11:02 AM, Christoph Hertzberg <
> chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > On 05.10.2015 18:08, Gabriel wrote:
> >
> > > Thanks a lot!
> > > I thought something is flawed, but
> > > I compared the assembler output with comments of the following
> > > (hopefully unflawed problem, random numbers, all the same )
> > >
> > > http://pastebin.com/qDvLGBfU
> > >
> > > I get close timings, but Eigen3 is still slower what can also be seen
> > > from the assembler output below
> > > Is my example still flawed, the Eigen internal dense assignment loop is
> > > not inlined?
> >
> > Unfortunately, GCC sometimes fails to properly optimize code inside the
> > main function. After moving your code into a different function, I get
> > exactly the same assembly (except for a cmovle/cmovs difference, because
> > you put the zero in front and not at the end, in the Eigen version).
> > If you still experience speed-differences, it's because the second loop
> > can work with already initialized caches.
> >
> > Christoph
> >
> >
> >
> >
> >
> > --
> >   Dipl. Inf., Dipl. Math. Christoph Hertzberg
> >
> >   Universität Bremen
> >   FB 3 - Mathematik und Informatik
> >   AG Robotik
> >   Robert-Hooke-Straße 1
> >   28359 Bremen, Germany
> >
> >   Zentrale: +49 421 178 45-6611
> >
> >   Besuchsadresse der Nebengeschäftstelle:
> >   Robert-Hooke-Straße 5
> >   28359 Bremen, Germany
> >
> >   Tel.:    +49 421 178 45-4021
> >   Empfang: +49 421 178 45-6600
> >   Fax:     +49 421 178 45-4150
> >   E-Mail:  chtz@xxxxxxxxxxxxxxxxxxxxxxxx
> >
> >   Weitere Informationen: http://www.informatik.uni-bremen.de/robotik

--
 Dipl. Inf., Dipl. Math. Christoph Hertzberg

 Universität Bremen
 FB 3 - Mathematik und Informatik
 AG Robotik
 Robert-Hooke-Straße 1
 28359 Bremen, Germany

 Zentrale: +49 421 178 45-6611

 Besuchsadresse der Nebengeschäftstelle:
 Robert-Hooke-Straße 5
 28359 Bremen, Germany

 Tel.:    +49 421 178 45-4021
 Empfang: +49 421 178 45-6600
 Fax:     +49 421 178 45-4150
 E-Mail:  chtz@xxxxxxxxxxxxxxxxxxxxxxxx

 Weitere Informationen: http://www.informatik.uni-bremen.de/robotik