It would also help to have some idea how you installed and ran this - e.g., did you set mpi_paffinity_alone so that the processes would bind to their processors? That could explain the cpu vs. elapsed time since it helps the processes from being swapped out as much.
Ralph > 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 > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users >
