[gmx-developers] bOptFFT

[Erik Lindahl]

Hi,

The reason for this is that the optimization in FFTW2 uses slow  
wallclock timers, so it frequently took several minutes at the start  
of each run, which of course was a nuisance for short tests - that's  
why I enabled it optionally a long time ago.

However, FFTW3 uses step counters with cycle accuracy and thus does  
the same optimization in less than a second, which is thus always a  
good idea to use.

We also support Intel MKL and the Built-in FFTPACK now, so it's a bit  
unlogical to have an FFTW2-specific option in the mdp file - that's  
why it was disabled. My primary feeling is to remove the option, but  
I'm open to suggestions :-)

Cheers,

Erik



On Dec 22, 2006, at 2:59 PM, Ansgar Esztermann wrote:

> Hello everyone,
>
> the bOptFFT flag should tell fftw whether or not different algorithms
> are to be timed at runtime. However, that option is not passed on to
> the library. Instead, optimization is always on for fftw3 and always
> off for fftw2. Back in August, there has been some discussion on this
> via private email between Carsten Kutzner and David van der Spoel,
> among others.
>
> Unless someone else is already working on the problem, I would like to
> create a patch to fix this.
>
> Any objection?
>
>
>
> A.
>
>
> -- 
> Ansgar Esztermann
> Researcher & Sysadmin
> http://www.mpibpc.mpg.de/groups/grubmueller/start/people/aeszter/ 
> index.shtml
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