IBM Power Systems 775 Manual page 26

Packet processing
The HFI is the interface between the POWER7 chip quads and the cluster network, and is
responsible for moving data between the PowerBus and the ISR. The data is in various
formats, but packets are processed in the following manner:
Send
– Pulls or receives data from PowerBus-attached devices in a POWER7 chip
– Translates data into network packets
– Injects network packets into the cluster network via the ISR
Receive
– Receives network packets from the cluster network via the ISR
– Translates them into transactions
– Pushes the transactions to PowerBus-attached devices in a POWER7 chip
Packet ordering
– The HFIs and cluster network provide no ordering guarantees among packets. Packets
that are sent from the same source window and node to the same destination window
and node might reach the destination in a different order.
Figure 1-6 shows two HFIs cooperating to move data from devices that are attached to one
PowerBus to devices attached to another PowerBus through the Cluster Network.
.
POWER7
Chip
Hub
Chip
ISR Network
Figure 1-6 HFI moving data from one quad to another quad
HFI paths: The path between any two HFIs might be indirect, thus requiring multiple hops
through intermediate ISRs.
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IBM Power Systems 775 for AIX and Linux HPC Solution
...
Proc, Proc,
Mem
caches caches
POWER7 Coherency Bus
POWER7
Link
POWER7 Coherency Bus
HFI HFI
ISR
...
Proc,
caches
POWER7
Chip
POWER7 Coherency Bus
POWER7 Coherency Bus
Hub
Chip
HFI
ISR ISR
Proc,
Mem
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POWER7
Link
HFI
ISR
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