IBM Power Systems 775 Manual page 135

Important: The path between any two HFIs might be indirect, requiring multiple hops
through intermediate ISRs.
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Proc, ... Proc,
caches caches
P7 Chip
Power Bus
WXYZ
Power Bus
Torrent
Chip
ISR Network
Figure 2-6 HFI moving data from one quad to another
Selecting the HFI route mode
With the HFI, the route of each packet is chosen by the hardware by default, and is usually a
direct route to the destination. However, you specify a different route mode that is appropriate
for your system by using the MP_FIFO_ROUTE_MODE or MP_RDMA_ROUTE_MODE
environment variables (you also can use the -fifo-route_mode or -rdma_route_mode
command line flags).
Choosing the appropriate route mode helps you increase outgoing bandwidth and avoid
traffic bottlenecks in the network.
The MP_FIFO_ROUTE_MODE and MP_RDMA_ROUTE_MODE route modes include the
following attributes:
Hardware direct (hw_direct)
Software indirect (sw_indirect)
Hardware direct striped (hw_direct_striped)
Hardware indirect (hw_indirect)
You choose to let PAMI/LAPI select the preferred route for the application that is most
appropriate, based on the configuration of the system. In particular, the software indirect
value allows PAMI/LAPI to select an indirect route to the destination when the origin and
destination tasks are on different supernodes.
Mem
link
HFI HFI
ISR
ISR
Proc, ... Proc,
caches caches
P7 Chip
Power Bus
WXYZ
link
Power Bus
Torrent
Chip
HFI HFI
ISR
ISR
Chapter 2. Application integration
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