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From: Robin Humble (rjh+openmpi_at_[hidden])
Date: 2007-01-18 04:00:57


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
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