Thank you very much Mi and Lenny for your detailed replies. I believe I can summarize the infos to allow for 'Working with a QS22 CellBlade cluster' like this: - Yes, messages are efficiently handled with "-mca btl openib,sm,self" - Better to go to the OMPI-1.3 version ASAP - It is currently more efficient/easy to use numactl to control processor affinity on a QS22.
So far so good. One question remains: how could I monitor in details message passing thru IB (on one side) and thru SM (on the other side) thru the use of mca parameters, please ? Additionnal info about the verbosity level of this monitoring will be highly appreciated ... A lengthy travel inside the list of such parameters provided by ompi_info did not enlighten me (there are so many xxx_sm_yyy type params that I don't know which could be the right one ;-) Thanks in advance for your hints, Best Regards, Gilbert. On Thu, 23 Oct 2008, Mi Yan wrote: > > 1. MCA BTL parameters > With "-mca btl openib,self", both message between two Cell processors on > one QS22 and messages between two QS22s go through IB. > > With "-mca btl openib,sm,slef", message on one QS22 go through shared > memory, message between QS22 go through IB, > > Depending on the message size and other MCA parameters, it does not > guarantee message passing on shared memory is faster than on IB. E.g. > the bandwidth for 64KB message is 959MB/s on shared-memory and is 694MB/s > on IB; the bandwidth for 4MB message is 539 MB/s and 1092 MB/s on IB. > The bandwidth of 4MB message on shared memory may be higher if you tune > some MCA parameter. > > 2. mpi_paffinity_alone > "mpi_paffinity_alone =1" is not a good choice for QS22. There are two > sockets with two physical Cell/B.E. on one QS22. Each Cell/B.E. has two > SMT threads. So there are four logical CPUs on one QS22. CBE Linux > kernel maps logical cpu 0 and 1 to socket1 and maps logical cpu 1 and 2 to > socket 2. If mpi_paffinity_alone is set to 1, the two MPI instances > will be assigned to logical cpu 0 and cpu 1 on socket 1. I believe this is > not what you want. > > A temporaily solution to force the affinity on QS22 is to use > "numactl", E.g. assuming the hostname is "qs22" and the executable is > "foo". the following command can be used > mpirun -np 1 -H qs22 numactl -c0 -m0 foo : -np 1 -H qs22 > numactl -c1 -m1 foo > > In the long run, I wish CBE kernel export CPU topology in /sys and > use PLPA to force the processor affinity. > > Best Regards, > Mi > > > > > "Lenny > Verkhovsky" > <lenny.verkhovsky To > @gmail.com> "Open MPI Users" > Sent by: <us...@open-mpi.org> > users-bounces@ope cc > n-mpi.org > Subject > Re: [OMPI users] Working with a > 10/23/2008 05:48 CellBlade cluster > AM > > > Please respond to > Open MPI Users > <users@open-mpi.o > rg> > > > > > > > Hi, > > > If I understand you correctly the most suitable way to do it is by > paffinity that we have in Open MPI 1.3 and the trank. > how ever usually OS is distributing processes evenly between sockets by it > self. > > There still no formal FAQ due to a multiple reasons but you can read how to > use it in the attached scratch ( there were few name changings of the > params, so check with ompi_info ) > > shared memory is used between processes that share same machine, and openib > is used between different machines ( hostnames ), no special mca params are > needed. > > Best Regards > Lenny, > > > > > > > > On Sun, Oct 19, 2008 at 10:32 AM, Gilbert Grosdidier <gro...@mail.cern.ch> > wrote: > Working with a CellBlade cluster (QS22), the requirement is to have one > instance of the executable running on each socket of the blade (there are > 2 > sockets). The application is of the 'domain decomposition' type, and each > instance is required to often send/receive data with both the remote > blades and > the neighbor socket. > > Question is : which specification must be used for the mca btl component > to force 1) shmem type messages when communicating with this neighbor > socket, > while 2) using openib to communicate with the remote blades ? > Is '-mca btl sm,openib,self' suitable for this ? > > Also, which debug flags could be used to crosscheck that the messages > are > _actually_ going thru the right channel for a given channel, please ? > > We are currently using OpenMPI 1.2.5 shipped with RHEL5.2 (ppc64). > Which version do you think is currently the most optimised for these > processors and problem type ? Should we go towards OpenMPI 1.2.8 > instead ? > Or even try some OpenMPI 1.3 nightly build ? > > Thanks in advance for your help, Gilbert. > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > (See attached file: RANKS_FAQ.doc) > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- *---------------------------------------------------------------------* Gilbert Grosdidier gilbert.grosdid...@in2p3.fr LAL / IN2P3 / CNRS Phone : +33 1 6446 8909 Faculté des Sciences, Bat. 200 Fax : +33 1 6446 8546 B.P. 34, F-91898 Orsay Cedex (FRANCE) ---------------------------------------------------------------------
