View figure.
The SP system partitioning can be used with the 16-port or 8-port SP Switch. It is not supported with the SP Switch2.
Actually, your choice in Example 1 was not necessarily as simple as suggested. A full switch board consists of 8 switch chips as shown in Figure 30. Each chip has 8 ports to which nodes and other switch chips can connect.
Precisely 4 of the switch chips can have nodes connected to them, as on the left side of the board in Figure 30. These chips are called node switch chips. Due to physical choices made in the SP frame, the nodes are connected as shown in the figure. Notice the following:
Figure 30. Full switch board
View figure.
Chips 0-3 are called link switch chips, and are also used in multi-frame systems to connect the various switch boards to each other using ports not shown in the figure.
Systems with switches are assumed to be used in performance-critical parallel computing. One major objective in partitioning a system with a switch is to keep the switch communication traffic in one switch partition from interfering with that of another. In order to ensure this, each switch chip is placed completely in one system partition.
Any link which joins switch chips in different partitions is disabled, so traffic of one partition cannot enter the physical bounds of another partition. The result of the partitioning choice you made in Example 1 is shown in Figure 31. Notice that the links from Chip 7 are missing in the diagram, indicating they have been logically removed from the active configuration, or disabled.
Figure 31. Nodes 11, 12, 15, and 16 partitioned off
View figure.
If your system contains the low cost SP Switch-8, your system partitioning capabilities are restricted. The SP Switch-8, has only 2 chips with nodes attached. So, if you have the maximum 8 nodes attached to the switch, you have 2 possible configurations: a single-partition 8-node system, or 2 system partitions of 4 nodes each.
One main consideration when planning for system partitions is the use of a switch. Partitioning, however, is also applicable to switchless systems. If you have a switchless system, and later add a switch, you might have to rethink your system partition choice. In fact you might want to reinstall the ssp.top file set so that any special switchless configurations you have constructed are removed from the system.
If you choose one of the supplied layouts, your partitioning choice is switch smart: your layout will still be usable when the switch arrives. This is because the predefined layouts are constrained to be usable in a system with an SP Switch.
Such a layout might be unsatisfactory, however, for your switchless environment, in which case you can use the System Partitioning Aid to build your own layout.