User guide

4–Running MPI on QLogic Adapters
Open MPI
IB0054606-02 A 4-19
IPATH_NO_CPUAFFINITY When set to 1, the PSM library will skip trying to
set processor affinity. This is also skipped if the
processor affinity mask is set to a list smaller than
the number of processors prior to MPI_Init() being
called. Otherwise the initialization code sets cpu
affinity in a way that optimizes cpu and memory
locality and load.
Default: Unset
IPATH_PORT Specifies the port to use for the job, 1 or 2.
Specifying 0 will autoselect IPATH_PORT.
Default: Unset
IPATH_UNIT This variable is for context sharing. When multiple
IB devices are present, and the IPATH_UNIT envi-
ronment variable is set, the number of IB contexts
made available to MPI jobs will be restricted to the
number of contexts available on that unit. By
default, IPATH_UNIT is unset and contexts from
all configured units are made available to MPI jobs
in round robin order.
Default: Unset
IPATH_HCA_SELECTION_ALG This variable provides user-level support to spec-
ify HCA/port selection algorithm through the envi-
ronment variable. The default option is a round
robin that allocates MPI processes to the HCAs in
an alternating or round robin fashion. The older
mechanism option is packed that fills all contexts
on one HCA before allocating from the next HCA.
For example: In the case of using two single-port
HCAs, the default or
IPATH_HCA_SELECTION_ALG= Round Robin
setting, will allow 2 or more MPI processes per
node to use both HCAs and to achieve perfor-
mance improvements compared to what can be
achieved with one HCA.
Default: Round Robin
IPATH_SL Service Level for QDR Adapters, these are used
to work with the switch's Vfabric feature.
Default: Unset
Table 4-6. Environment Variables Relevant for any PSM (Continued)
Name Description