Just a quick note - I have noticed the same behavior with LAM-MPI, but not with MPICH. Jacques
2008/12/5 Paul Edwards <[EMAIL PROTECTED]> > 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 >> > > > _______________________________________________ > ParaView mailing list > [email protected] > http://www.paraview.org/mailman/listinfo/paraview > >
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