Dear Jeff, Dear All, we know about *mpi_yield_when_idle* parameter [1]. We read [2]. You're right, > if an MPI application is waiting a long time for messages, > perhaps its message passing algorithm should be re-designed ... but we cannot spur the ParaView/VTK developer to rewrite their software famous for busy-wait on any user mouse move with N x 100% CPU load [3].
It turned out that a) (at least some) spin time is on MPI_Barrier call (waitin' user interaction) b) for Intel MPI and MPICH we found a way to disable this busy wait [4] c) But, for both 'pvserver' and minimal example (attached), we were not able to stop the busy waiting with Open MPI: setting *mpi_yield_when_idle* parameter to '1' just seem to move the spin activity from userland to kernel, with staying at 100%, cf. attached screenshots and [5]. The behaviour is the same for 1.10.4 and 2.0.2. Well, The Question: is there a way/a chance to effectively disable the busy wait using Open MPI? Best, Paul Kapinos [1] http://www.open-mpi.de/faq/?category=running#force-aggressive-degraded [2] http://blogs.cisco.com/performance/polling-vs-blocking-message-passingprogress [3] https://www.paraview.org/Wiki/Setting_up_a_ParaView_Server#Server_processes_always_have_100.25_CPU_usage [4] https://public.kitware.com/pipermail/paraview-developers/2017-October/005587.html [5] https://serverfault.com/questions/180711/what-exactly-do-the-colors-in-htop-status-bars-mean -- Dipl.-Inform. Paul Kapinos - High Performance Computing, RWTH Aachen University, IT Center Seffenter Weg 23, D 52074 Aachen (Germany) Tel: +49 241/80-24915
! Paul Kapinos 06.10.2017 - ! IT Center RWTH Aachen, www.itc.rwth-aachen.de ! ! MPI-busy-waiting-World ! PROGRAM PK_MPI_Test USE MPI IMPLICIT NONE !include "mpif.h" INTEGER :: my_MPI_Rank, ierr CALL MPI_INIT(ierr) CALL MPI_COMM_RANK( MPI_COMM_WORLD, my_MPI_Rank, ierr ) IF (my_MPI_Rank == 0) CALL Sleep(20) CALL MPI_BARRIER(MPI_COMM_WORLD, ierr) ! all but rank=0 processes busy-wait here... CALL MPI_FINALIZE(ierr) END PROGRAM PK_MPI_Test
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