User guide

4–Running MPI on QLogic Adapters
Open MPI
4-8 IB0054606-02 A
The default hardware context/CPU mappings can be changed on the QDR IB
Adapters (QLE734x). See “IB Hardware Contexts on the QDR IB Adapters” on
page 4-8 for more details.
Context sharing is enabled by default. How the system behaves when context
sharing is enabled or disabled is described in “Enabling and Disabling Software
Context Sharing” on page 4-9.
When running a job in a batch system environment where multiple jobs may be
running simultaneously, it is useful to restrict the number of IB contexts that are
made available on each node of an MPI. See “Restricting IB Hardware Contexts in
a Batch Environment” on page 4-10.
Errors that may occur with context sharing are covered in “Context Sharing Error
Messages” on page 4-11.
There are multiple ways of specifying how processes are allocated. You can use
the mpihosts file, the -np and -ppn options with mpirun, and the
MPI_NPROCS and PSM_SHAREDCONTEXTS_MAX environment variables. How
these all are set are covered later in this document.
IB Hardware Contexts on the QDR IB Adapters
On the QLE7340 and QLE7342 QDR adapters, adapter receive resources are
statically partitioned across the IB contexts according to the number of IB contexts
enabled. The following defaults are automatically set according to the number of
online CPUs in the node:
For four or less CPUs: 6 (4 + 2)
For five to eight CPUs: 10 (8 + 2)
For nine or more CPUs: 18 (16 + 2)
The one additional context on QDR adapters are to support the kernel on each
port.
Table 4-5. Available Hardware and Software Contexts
Adapter
Available Hardware
Contexts (same as number
of supported CPUs)
Available Contexts when
Software Context Sharing is
Enabled
QLE7342/
QLE7340
16 64