Thanks Jeff Ian Hutchinson http://www.psfc.mit.edu/people/hutch/ -
Date: Sat, 8 Dec 2012 14:46:03 -0600 From: Jeff Hammond <[email protected]> Reply-To: [email protected] To: [email protected] Subject: Re: [mpich-discuss] Bug fix for dims_create
Hi Ian,
I have created https://trac.mpich.org/projects/mpich/ticket/1765 on your behalf so that this issue can be tracked by the developers.
Best,
Jeff
On Sat, Dec 8, 2012 at 2:07 PM, Ian Hutchinson <[email protected]> wrote:
The file src/mpi/topo/dims_create.c contains the code that determines the result of
MPI_DIMS_CREATE
It contains a bug which causes it to produce improper distributions of the processes among dimensions that do not satisfy the objective of being "as close to each other as possible". For example, if called in 3-dimensions, with 16 nodes, the topology returned is 4, 4, 1. It ought to be 4, 2, 2.
This bug is caused by some longstanding cobbled-together code that is called when all the factors of the nnodes are 2 (which is not an unusual case).
I attach (and include below) a patch to correct this bug. It would be great if it could find its way into the distribution.
Thanks Ian Hutchinson http://www.psfc.mit.edu/people/hutch/
=========================================================================
--- dims_create.c.dist 2012-12-08 13:46:46.000000000 -0500 +++ dims_create.c 2012-12-08 13:48:02.000000000 -0500 @@ -317,28 +317,22 @@ int cnt = factors[0].cnt; /* Numver of factors left */ int cnteach = ( cnt + dims_needed - 1 ) / dims_needed; int factor_each; - - factor_each = factor; - for (i=1; i<cnteach; i++) factor_each *= factor;
- for (i=0; i<ndims; i++) { - if (dims[i] == 0) { - if (cnt > cnteach) { - dims[i] = factor_each; - cnt -= cnteach; - } - else if (cnt > 0) { - factor_each = factor; - for (j=1; j<cnt; j++) - factor_each *= factor; - dims[i] = factor_each; - cnt = 0; - } - else { - dims[i] = 1; - } + for (i=0;i<ndims;i++){ + if(dims[i]==0)dims[i]=-1; + } + i=0; + while(cnt > 0){ + if(dims[i] < 0){ + dims[i]=dims[i]*factor; + cnt--; } + if(++i >= ndims)i=0; + } + for (i=0;i<ndims;i++){ + if(dims[i] < 0)dims[i]=-dims[i]; } + } else { /* Here is the general case. */ _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss