Re: [eigen] Performance difference icc <-> gcc, EIGEN_STRONG_INLINE

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi!

We could easily remove EIGEN_COMP_ICC from the cases where 
EIGEN_STRONG_INLINE is a __force_inline:
https://bitbucket.org/eigen/eigen/src/default/Eigen/src/Core/util/Macros.h#Macros.h-755

But I don't know the history of this, i.e., if it was necessary for 
older ICC versions. Or if it is necessary at other places.

Did you try to reduce your code to a minimal example where the 
performance drop occurs?


Regarding mbsolve: Sure, please give us a small description text and 
tell which category you want to get listed in.

Cheers,
Christoph


On 13/03/2019 03.10, Michael Riesch wrote:
> Hello all,
>
> Thank you very much for your work on Eigen. We found it very useful for 
> our simulation software mbsolve [1] (BTW maybe you would like to add it 
> to the projects list that uses the Eigen library).
>
> The code I am working on at the moment consists mostly of dense 
> matrix-matrix and matrix-vector multiplications. I compiled the code 
> with both Intel compiler 19 and gcc 6.3.0 and found that there is a 
> strange performance difference. Unless I define
>
> #EIGEN_STRONG_INLINE inline
>
> the binary compiled by icc is ~13x slower. The gcc binary performance 
> remains the same, as inline seems to be the standard setting of this 
> macro for gcc.
>
> Why can this behavior occur? Or, alternatively, which possible 
> anti-pattern could be the cause of this performance difference?
>
> Any hints are welcome. If you need more information, please let me know.
>
> Thanks in advance and best regards,
> Michael
>
> [1] https://github.com/mriesch-tum/mbsolve


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