[mpich-discuss] Create account for bug tracker

[n n]

I do not actually need this functionality, but can you show example of
robust code, which will work for mpi_scan in all cases?
And can you clarify, why the order of output is not preserved, as in
openmpi version?

On Wed, Dec 19, 2012 at 1:52 AM, Dave Goodell <goodell at mcs.anl.gov> wrote:

> This scan operator is known to be buggy, unfortunately.  It will not do
> the correct thing for many (entirely valid) scan implementation patterns.
>  It's something that ought to be fixed in the next version of the MPI
> standard (it fell through the cracks in the MPI-3 process).
>
> Do you actually need this functionality?  If so, I can describe how to
> implement it in a way that will be robust.  Alternatively, most segmented
> scan algorithms assume an "edge triggered" segmented scan, rather than a
> "level" triggered one like what is described in the MPI standard.
>
> -Dave
>
> On Dec 18, 2012, at 2:06 PM CST, n n wrote:
>
> > Ok.
> > Here is detailed explanation.
> > There is example 5.22 on page 182 in mpi22-report.pdf, which can be
> found here http://www.mpi-forum.org/docs/docs.html
> >
> > Here is test code http://pastebin.com/ZhYfhDVK (same code here
> http://www.everfall.com/paste/id.php?0b7mgk2zh0xg, just in case)
> >
> > If i run this code using openmpi in archlinux, i get the following
> result (as expected, in accordance with info from mpi22-report.pdf).
> >
> > mpicc code.c -o openmpi_version (mpicc from openmpi package, mpich is
> not installed in archlinux)
> > mpirun -n 8 ./openmpi_version
> > 0       0 1.000000
> > 1       0 2.000000
> > 2       1 1.000000
> > 3       1 2.000000
> > 4       1 3.000000
> > 5       0 1.000000
> > 6       0 2.000000
> > 7       1 1.000000  <===== 1, as expected
> >
> > But if i run this code using mpich2 in ubuntu 10.04, (mpich package
> version 1.2.1.1), i get unexpected result. It was also tested in
> mpich2-1.4.1p1 and mpich2-1.5 in Windows 7 and Ubuntu 10.04.2 respectively.
> > mpicc code.c -o mpich_version (mpicc from mpich2 package, openmpi is not
> installed in ubuntu)
> > mpirun -n 8 ./mpich_version
> > 0       0 1.000000
> > 1       0 2.000000
> > 2       1 1.000000
> > 5       0 1.000000
> > 3       1 2.000000
> > 4       1 3.000000
> > 6       0 2.000000
> > 7       1 3.000000 <===== expected to be 1
> >
> >
> > Also, in openmpi version output is sorted, in accordance with code in
> lines 60-73 (see pastebin), but in mpich2 this does not work as expected
> too.
> >
> > On Tue, Dec 18, 2012 at 11:25 PM, Dave Goodell <goodell at mcs.anl.gov>
> wrote:
> > On Dec 18, 2012, at 4:47 AM CST, n n wrote:
> >
> > > I think, i've found a bug in function mpi_scan
> >
> > Would you care to share any details of the bug on the mailing list?
>  Forgive my caution, but you have a somewhat spammy looking email address
> and email name and wrote a rather terse email...
> >
> > -Dave
> >
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