I/O slow (buffered?) ; can I change this?

[Rob]

--- Jerry DeLisle <jvdelisle@verizon.net> wrote:

> Rob wrote:
> > Hi,
> > 
> > When I compile my software with Gfortran (from
> > SVN, 4.1.2 20061215 (prerelease)), the print
> > output to the terminal is extremely slow and
> > comes in bursts.
> > I guess Gfortran defaults to some kind of
> > buffering.
> > 
> > When I use another compiler (e.g. Intel's ifort),
> > then output comes immediately without delay. So
> > obviously the slow I/O is related to Gfortran.
> > 
> > Is there a way to tell Gfortran to stop or reduce
> > the I/O buffering?
> 
> What system are you running on?
> 
> Can you give an example of the code producing the
> output that you are observing?

This is on an alpha system, for which at present
the only available compiler is GFortran.

I myself know almost nothing about fortran, but I
compile the physics ab initio package VASP written
in fortran: http://cms.mpi.univie.ac.at/vasp
(this is commercial software).

I need the compiler flag "-mfp-trap-mode=su", in
order to prevent a segfault signal when running
the executable.

So I don't have a short piece of code that
demonstrates the slow I/O. I only compare the
behaviour of the executable on my alpha system with
Gfortran, and the same executable on Linux/Pentium
system compiled with Intel's ifort.

On the Linux system, the output comes gradually,
but on the alpha system it comes in bursts.

Hence I wondered whether a compiler flag could
change this behaviour.

Rob.


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