[gmx-users] GROMACS compilation problem on IBM AIX

[Gerrit Groenhof]

Hi again Jithesh,

> WHen you get everything running it could still be owrthwhile to
> recompile everything for power4.

ANd then compare the outcome with the outcome obtained from gromacs
compiled with -O2. That it just runs fine doesn't say anything yet.  I
had the same. The simulations would just go and produce output which
did not seem too bad. But only when I compared with results obtained
on other platforms I saw that there was something wrong. The problem
with the -O3 option of the xlc compiler I experienced was that the
statements in certain functions were re-ordered. For instance in
sum_ekin (tgroup.c), it was clear that the statement were executed in
the wrong order. ONly after adding print statements, the function
would work fine with -O3. IN fact I remember that when using -O3 the
compiler by default warns the user that this can happen.

Have fun,

Gerrit

 
> 
> > thanks & regards
> > Jithesh
> >  
> > gmx-users at gromacs.org wrote:
> > 
> > On Monday, Feb 3, 2003, at 09:43 US/Pacific, David van der Spoel wrote:
> > 
> > > On Mon, 2003-02-03 at 15:16, Gerrit Groenhof wrote:
> > >> Hi Jithesh,
> > >>
> > >> I am not sure, but from your benchmark it seems gromacs is not
> > >> compiled properly. I had the same problem on an IBM SP3 (4?). changing
> > >> the optimization from O3 to O2 did the trick. What also works is to
> > >> change from the IBM xlc compiler to the gnu gcc compiler.
> > >>
> > > And it is also very important to check that all libraries are compiled
> > > with the same options (for hardware specifics: the processor type). If
> > > you compile part for power3 (e.g. fftw) and part for power4 (gromacs)
> > > your simulations will die.
> > >
> > > Check an option in fftw compilation, it could be that they default for
> > > the wrong architecture.,
> > 
> > Yeah, but I think it will just default to pwr2 which should be fine 
> > (although not as fast).
> > 
> > There might indeed be a problem with the IBM compilers; if anybody can 
> > provide
> > access to a power4 system I'll have a go at debugging it.
> > 
> > Cheers,
> > 
> > Erik
> > 
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> -- 
> Groeten, David.
> ________________________________________________________________________
> Dr. David van der Spoel, 	Dept. of Cell & Mol. Biology
> Husargatan 3, Box 596,  	75124 Uppsala, Sweden
> phone:	46 18 471 4205		fax: 46 18 511 755
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