argh. attached. cheers, robin
On Thu, Jan 18, 2007 at 03:52:19AM -0500, Robin Humble wrote: >On Wed, Jan 17, 2007 at 08:55:31AM -0700, Brian W. Barrett wrote: >>On Jan 17, 2007, at 2:39 AM, Gleb Natapov wrote: >>> On Wed, Jan 17, 2007 at 04:12:10AM -0500, Robin Humble wrote: >>>> basically I'm seeing wildly different bandwidths over InfiniBand 4x DDR >>>> when I use different kernels. >>> Try to load ib_mthca with tune_pci=1 option on those kernels that are >>> slow. >>when an application has high buffer reuse (like NetPIPE), which can >>be enabled by adding "-mca mpi_leave_pinned 1" to the mpirun command >>line. > >thanks! :-) >tune_pci=1 makes a huge difference at the top end, and >-mca mpi_leave_pinned 1 adds lots of midrange bandwidth. > >latencies (~4us) and the low end performance are all unchanged. > >see attached for details. >most curves are for 2.6.19.2 except the last couple (tagged as old) >which are for 2.6.9-42.0.3.ELsmp and for which tune_pci changes nothing. > >why isn't tune_pci=1 the default I wonder? >files in /sys/module/ib_mthca/ tell me it's off by default in >2.6.9-42.0.3.ELsmp, but the results imply that it's on... maybe PCIe >handling is very different in that kernel. > >is ~10Gbit the best I can expect from 4x DDR IB with MPI? >some docs @HP suggest up to 16Gbit (data rate) should be possible, and >I've heard that 13 or 14 has been achieved before. but those might be >verbs numbers, or maybe horsepower >> 4 cores of 2.66GHz core2 is >required? > >>It would be interesting to know if the bandwidth differences appear >>when the leave pinned protocol is used. My guess is that they will > >yeah, it definitely makes a difference in the 10kB to 10mB range. >at around 100kB there's 2x the bandwidth when using pinned. > >thanks again! > >> Brian Barrett >> Open MPI Team, CCS-1 >> Los Alamos National Laboratory > >how's OpenMPI on Cell? :) > >cheers, >robin >_______________________________________________ >users mailing list >us...@open-mpi.org >http://www.open-mpi.org/mailman/listinfo.cgi/users
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