Re: [OMPI users] MX MPI latency measurements

[George Bosilca]

If you use one of the latest version of MX (such as 1.2.0f) there will be less than 0.15 micro-second difference between the MTL and BTL MX. This version of MX allow us to do the matching outside the NIC, which decrease the overhead for small messages. In terms of bandwidth the BTL MX is somehow faster (40Mbs more than the MTL) on a 2Gbs network.

  Thanks,
    george.

On Jun 6, 2007, at 5:23 PM, Tim Prins wrote:

Note that since you are setting OMPI_MCA_pml to cm, OMPI_MCA_btl will have no effect. You may try setting OMPI_MCA_pml=ob1, and trying your measurements again, but we generally get better performance with the cm pml than then ob1

pml.

Tim

On Wednesday 06 June 2007 12:54:26 pm George Bosilca wrote:

Which one is the latency with Open MPI ? Which version of Open MPI ?

You might want to use OMPI_MCA_btl=mx,self to see if it makes any
difference.

   Thanks,
     george.

On Jun 6, 2007, at 12:26 PM, Maestas, Christopher Daniel wrote:

With 2 nodes using 1.1.7 with the patch we measured (using mpich-mx
1.2.7..4):
        3.07us

With mx 1.2.1-rc18 we measure:
        3.69 us
And with mpich-mx 1.2.7..4 we see:
        3.20us

Our Open MPI settings:
---
# env | grep OMPI
OMPI_MCA_pml=cm
OMPI_MCA_mpi_keep_hostnames=1
OMPI_MCA_oob_tcp_include=eth0
OMPI_MCA_btl=mx,sm,self

Does anyone know why the latency would be slightly higher using
Open MPI
versus MPICH-MX?

Thanks,
-cdm


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