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Figure 2-8 Striping
Data striping
When parallel jobs are run, it is possible to stripe data through multiple adapter windows. This
striping is supported for both IP and User Space protocols.
If the system has more than one switch network, the resource manager allocates adapter
windows from multiple adapters. A switch network is the circuit of adapters that connect to the
same interconnect. One window is assigned to an adapter, with one adapter each selected
from a different switch network.
If the system has only one switch network, the adapter windows are most likely allocated from
different adapters, if there are sufficient windows available on each adapter. If there are not
enough windows available on one of the adapters, all of the adapter windows might be
allocated from a single adapter.
PAMI (or LAPI) manages communication among multiple adapter windows. By using
resources that are allocated by a resource manager, PAMI/LAPI opens multiple user space
windows for communication. Every task of the job opens the same number of user space
windows, and a particular window on a task communicates only with the corresponding
window on other tasks. These windows form a set of virtual networks in which each virtual
network consists of a window from each task that communicates with the corresponding
windows from the other tasks. The distribution of data among the various windows on a task
is referred to as striping, which improves communication bandwidth performance for
PAMI/LAPI clients.
To enable striping in user space mode, use environment variable settings that result in the
allocation of multiple instances. For a multi-network system, striping is done by setting
MP_EUIDEVICE to sn_all. On a single-network system with multiple adapters per operating
system image, striping is done by setting MP_EUIDEVICE to sn_single and setting
MP_INSTANCES to a value that is greater than 1.
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IBM Power Systems 775 for AIX and Linux HPC Solution
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