QLogic OFED+ Host Software User Guide, Rev. B

5–Using Other MPIs
Improving Performance of Other MPIs Over InfiniBand Verbs
uDAPL 1.2:
-genv I_MPI_DEVICE rdma:OpenIB-cma
uDAPL 2.0:
-genv I_MPI_DEVICE rdma:ofa-v2-ib
To help with debugging, you can add this option to the Intel mpirun command:
TMI:
-genv TMI_DEBUG 1
uDAPL:
-genv I_MPI_DEBUG 2
Further Information on Intel MPI
For more information on using Intel MPI, see: http://www.intel.com/
Improving Performance of Other MPIs Over
InfiniBand Verbs
Performance of MPI applications when using an MPI implementation over
InfiniBand Verbs can be improved by tuning the InfiniBand MTU size.
NOTE:
No manual tuning is necessary for PSM-based MPIs, since the PSM layer
determines the largest possible InfiniBand MTU for each source/destination
path.
The maximum supported MTU size of InfiniBand adapter cards is 4K.
Support for 4K InfiniBand MTU requires switch support for 4K MTU. The method
to set the InfiniBand MTU size varies by MPI implementation:
• Open MPI defaults to the lower of either the InfiniBand MTU size or switch
MTU size.
• MVAPICH defaults to an InfiniBand MTU size of 1024 bytes. This can be
over-ridden by setting an environment variable:
$ export VIADEV_DEFAULT_MTU=MTU4096
Valid values are MTU256, MTU512, MTU1024, MTU2048 and MTU4096. This
environment variable must be set for all processes in the MPI job. To do so,
use ~/.bashrc or use of /usr/bin/env.
5-14 D000046-005 B