Hi all, It just depends on how it is implemented with MPI. There will be lower latency if it spins in a loop waiting for a message. Here is a link to the FAQ which shows how you can stop this for OpenMPI:
http://www.open-mpi.org/faq/?category=running#oversubscribing http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded Regards, Paul 2008/12/5 John M. Patchett <[EMAIL PROTECTED]> > Hi Jens, > If I recall correctly, your observation lies in the type of hardware you > are using. I think some hardware allows a developer to leverage an > interrupt while some requires polling for a received message. Design > requirements for MPI to be fast with low latency usually (I presume) > outweigh lowering heat production. > > I think I first noticed this issue with mvapich when infiniband was new. I > don't think we had it with Myrinet 2000 or Gig-E. > > I also think ParaView is a normal mpi application, we just don't notice > machines spinning while waiting during batch processing, we just assume > they're working hard. > > > -John. > > On Dec 5, 2008, at 9:42 AM, Jens wrote: > > Hi John, >> >> thanks for your answer. That makes sense. "Normal" mpi-apps are probably >> not written to wait for more things to do - they are simply always busy. >> >> It is just a pity that the cluster has to run 100% producing a lot of >> heat for nothing. >> >> So the MPI-lib will probably not change this behavior :( ? (I am using >> open-mpi 1.2.8) >> >> Greetings >> Jens >> >> >> John M. Patchett schrieb: >> >>> Hi Jens, >>> Your pvserver is probably waiting on an MPI_Recv and your MPI >>> implementation is spinning. >>> You will note that process 0 probably isn't doing this, as the other >>> nodes are waiting on process 0 to send. >>> I have searched this problem all the way to the MPI developers as it's >>> easy to replicate without paraview and the MPI guys assure me the >>> alternatives are worse. >>> -John. >>> >>> On Dec 5, 2008, at 8:42 AM, Jens wrote: >>> >>> Hi, >>>> >>>> if I run "mpirun -np 4 ./pvserver" on our cluster-node and connect from >>>> my client, this pvserver always shows 100% cpu usage - even if I do >>>> nothing at the client. >>>> >>>> Seems to me as if there is a loop waiting for the client to ask for >>>> action - but this loop is calling no wait/sleep function. >>>> >>>> Greetings >>>> Jens >>>> _______________________________________________ >>>> ParaView mailing list >>>> [email protected] >>>> http://www.paraview.org/mailman/listinfo/paraview >>>> >>> >>> > _______________________________________________ > ParaView mailing list > [email protected] > http://www.paraview.org/mailman/listinfo/paraview >
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