Your Intel processors are I assume not the new Nehalem/I7 ones? The older quad-core ones are seriously memory bandwidth limited when running a memory intensive application. That might explain why using all 8 cores per node slows down your calculation.
Why do you get such a difference between cpu time and elapsed time? Is your code doing any file IO or maybe waiting for one of the processors? Do you use non-blocking communication wherever possible? Regards, Mattijs On Wednesday 04 March 2009 05:46, Sangamesh B wrote: > Hi all, > > Now LAM-MPI is also installed and tested the fortran application by > running with LAM-MPI. > > But LAM-MPI is performing still worse than Open MPI > > No of nodes:3 cores per node:8 total core: 3*8=24 > > CPU TIME : 1 HOURS 51 MINUTES 23.49 SECONDS > ELAPSED TIME : 7 HOURS 28 MINUTES 2.23 SECONDS > > No of nodes:6 cores used per node:4 total core: 6*4=24 > > CPU TIME : 0 HOURS 51 MINUTES 50.41 SECONDS > ELAPSED TIME : 6 HOURS 6 MINUTES 38.67 SECONDS > > Any help/suggetsions to diagnose this problem. > > Thanks, > Sangamesh > > On Wed, Feb 25, 2009 at 12:51 PM, Sangamesh B <forum....@gmail.com> wrote: > > Dear All, > > > > A fortran application is installed with Open MPI-1.3 + Intel > > compilers on a Rocks-4.3 cluster with Intel Xeon Dual socket Quad core > > processor @ 3GHz (8cores/node). > > > > The time consumed for different tests over a Gigabit connected > > nodes are as follows: (Each node has 8 GB memory). > > > > No of Nodes used:6 No of cores used/node:4 total mpi processes:24 > > CPU TIME : 1 HOURS 19 MINUTES 14.39 SECONDS > > ELAPSED TIME : 2 HOURS 41 MINUTES 8.55 SECONDS > > > > No of Nodes used:6 No of cores used/node:8 total mpi processes:48 > > CPU TIME : 4 HOURS 19 MINUTES 19.29 SECONDS > > ELAPSED TIME : 9 HOURS 15 MINUTES 46.39 SECONDS > > > > No of Nodes used:3 No of cores used/node:8 total mpi processes:24 > > CPU TIME : 2 HOURS 41 MINUTES 27.98 SECONDS > > ELAPSED TIME : 4 HOURS 21 MINUTES 0.24 SECONDS > > > > But the same application performs well on another Linux cluster with > > LAM-MPI-7.1.3 > > > > No of Nodes used:6 No of cores used/node:4 total mpi processes:24 > > CPU TIME : 1hours:30min:37.25s > > ELAPSED TIME 1hours:51min:10.00S > > > > No of Nodes used:12 No of cores used/node:4 total mpi processes:48 > > CPU TIME : 0hours:46min:13.98s > > ELAPSED TIME 1hours:02min:26.11s > > > > No of Nodes used:6 No of cores used/node:8 total mpi processes:48 > > CPU TIME : 1hours:13min:09.17s > > ELAPSED TIME 1hours:47min:14.04s > > > > So there is a huge difference between CPU TIME & ELAPSED TIME for Open > > MPI jobs. > > > > Note: On the same cluster Open MPI gives better performance for > > inifiniband nodes. > > > > What could be the problem for Open MPI over Gigabit? > > Any flags need to be used? > > Or is it not that good to use Open MPI on Gigabit? > > > > Thanks, > > Sangamesh > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Mattijs Janssens OpenCFD Ltd. 9 Albert Road, Caversham, Reading RG4 7AN. Tel: +44 (0)118 9471030 Email: m.janss...@opencfd.co.uk URL: http://www.OpenCFD.co.uk
