[gmx-developers] bOptFFT

Erik Lindahl lindahl at cbr.su.se
Fri Dec 22 19:03:07 CET 2006


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 :-)



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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