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

[Nate Yonkee <nathan.yonkee@xxxxxxxxx>]

Thanks for clearing that up Christoph. I'm always impressed with how beautiful Eigen is.

On Oct 5, 2015 11:30 AM, "Christoph Hertzberg" <chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

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