Re: [gentoo-dev] Re: [gentoo-commits] gentoo-x86 commit in sys-cluster/openmpi: ChangeLog openmpi-1.1.1.ebuild openmpi-1.2.4.ebuild

[Matthias Langer]

On Fri, 2007-12-14 at 12:13 +0000, Sébastien Fabbro wrote: 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 14/12/07 10:24, Matthias Langer wrote:
> >> On 02:10 Thu 13 Dec     , Justin Bronder (jsbronder) wrote:
> >>> 1.1                  sys-cluster/openmpi/openmpi-1.2.4.ebuild
> >>>
> >>> file : http://sources.gentoo.org/viewcvs.py/gentoo-x86/sys-cluster/openmpi/openmpi-1.2.4.ebuild?rev=1.1&view=markup
> >>> plain: http://sources.gentoo.org/viewcvs.py/gentoo-x86/sys-cluster/openmpi/openmpi-1.2.4.ebuild?rev=1.1&content-type=text/plain
> >
> > Why have you removed the "ifc" USE flag (as well as a few others), that
> > was present in the ebuilds that can still be found at bug 166787?
>
> For icc and  f90-typesafe, I advised him to do so on #gentoo-science.

Well, too bad that gfortran generates code that is often not even half
as fast as the code generated by ifc. Thus, there is a *very valid*
reason to prefer icc over gfortran when it comes to performance critical
software, which programs that use MPI almost always are. However, the
fortran eclass prefers gfortran over ifc even if both are installed
(which is fine by me as long as it can be overridden) and the
fortran-compiler-wrapper "mpif90/opal_wrapper" (which is a binary for
some reason) wrapps gfortran then.

For sure, something like
F77="ifort" FC="ifort" FFLAGS="-O3 -xO" emerge -av openmpi
still does the trick, but if i want that "f90-typesave" stuff back, this
line would have to be certainly a bit longer...

Maybe someone can explain to me what positive side effects the removal
of the ifc USE flag has - and why this flag is generally discouraged.

>
> ifc/icc use flags should be avoided (see bug #97929).
> Disabling f90-typesafe did not make much sense as a use flag once you
> have the fortran one enabled, but why --with-mpi-f90-size=medium"
> and "--with-f90-max-array-dim=4" disappeared I don't know.

The reason it disappeared is that it makes gfortran horribly slow when
compiling against mpi. This is not the case with ifc, and therefore the
old ebuild in bugzilla emitted a bold warning when emerging with
USE="-ifc f90-typesafe" but kept quiet if USE="ifc f90-typesave". Thus
it *did make sense* to control it with a USE flag, at least with the
"ifc" USE flag being around also.

> For the gm and gx flags, I don't know, and there is still a nocxx one.

I'm not qualified to talk about these flags as I've never used them.

Matthias