In principle if you use -ax... you get all the code paths so it will run on
multiple chip versions. This should be perfectly good. In practice though
you should be compiling specifically for each architecture you have these
days since the idea of a global 'i386/x86' instruction set is long dead. :-(
These days the acronyms include:
x86,x86_64,ia64,mmx,sse,sse2,sse3,ssse3,sse4.1,sse4.2,3dnow and lots more...
The issue is that these can make such a big performance improvement that we
should definitely be including them if we can.
> -----Original Message-----
> From: amber-developers-bounces.ambermd.org [mailto:amber-developers-
> bounces.ambermd.org] On Behalf Of Ben Roberts
> Sent: Friday, October 23, 2009 5:06 PM
> To: AMBER Developers Mailing List
> Subject: Re: [AMBER-Developers] SSE2 / SSE3 settings no longer used for
> ifort?
>
> On Fri, 2009-10-23 at 16:45 -0700, Ross Walker wrote:
> > Hi All,
> >
> > It seems that the config.h prepared by ./configure is no longer
> setting the
> > SSE2 / SSE3 optimization flags for the Intel compiler. This can
> reduce
> > performance by >30% in some cases. Does anyone know why this was
> turned off?
> >
> > Specifically this is things like:
> >
> > ifort -axWPS
> >
> > The problem is that different versions of the Intel compilers use
> different
> > sets of flags. Once again an example of the patients running the
> asylum.
> > However, we could set -fast as the default option which would turn
> on:
> >
> > -xP -O3 -ipo
> >
> > The ipo is a problem since it means all the optimization is done at
> link
> > stage and you lose all the benefits of parallel builds and each new
> make is
> > very expensive. We could specify
> >
> > -axWPS
> >
> > but a lot of this is now changed and deprecated in ifort >11.0
> >
> > Hence should we have an intel9 and intel10 target which uses -O3 -ip
> -axWPS
> > and an Intel11 target which uses -O3 -ip -
> axSSE4.2,SSE4.1,SSSE3,SSE3,SSE2
> >
> > Comments?
>
> Hi Ross,
>
> My immediate question (perhaps influenced by my recent development
> efforts on the Mac) is: How well supported are these new flags between
> platforms?
>
> Cheers,
> Ben
>
>
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Received on Fri Oct 23 2009 - 17:30:04 PDT
