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From: Sylvain Le Gall <sylvain@le-gall.net>
Subject: Re: ocamlmpi reduce_int_array, showstopper?
Date: Mon, 6 Sep 2010 10:51:37 +0000 (UTC)
Message-ID: <slrni89htp.skq.sylvain@gallu.homelinux.org>
References: <AANLkTimEra9gdaJRz4nwrRfMrz-VovAQLB7vPuN9fK9G@mail.gmail.com>
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X-Spam: no; 0.00; le-gall:01 ocamlmpi:01 showstopper:01 mikelin:01 ocamlmpi:01 trivial:01 mikelin:01 uname:01 usr:01 bug:01 commited:01 2009:98 1.2:98 wrote:01 integer:01 

On 04-09-2010, Mike Lin <mikelin@MIT.EDU> wrote:
> Hi Sylvain, Xavier,
> I have encountered what seems to be a serious problem with
> reduce_int_array in ocamlmpi, namely, in a trivial test case it
> successfully returns incorrect results. This is my test code
>

[...]

>
> [mikelin@honest3 ~/]$ uname -a
> Linux honest3.ncsa.uiuc.edu 2.6.18-92.1.10.el5_lustre.1.6.6smp-perfctr
> #7 SMP Tue Nov 10 10:41:00 CST 2009 x86_64 x86_64 x86_64 GNU/Linux
> [mikelin@honest3 ~/]$ which mpiexec
> /usr/local/mvapich2-1.2-intel-ofed-1.2.5.5/bin/mpiexec
>
> see also: http://www.ncsa.illinois.edu/UserInfo/Resources/Hardware/Intel64Cluster/
>
> I know the ocamlmpi code has been stable for some time, but I wonder
> if it's been tested on x86_64? Let me know if you're able to reproduce
> this.
>

I can confirm the bug. I have commited a fix in the svn. Though, I am
not an MPI expert.

I think the problem was related to a double in-place re-encoding of
integer in the array. I'll wait for Xavier review to do a release.

Regards,
Sylvain Le Gall