Expand Configuration and Management Manual (G06.24+)

Tuning
Expand Configuration and Management Manual—523347-008
20-18
Multi-CPU Paths
A process on \A in CPU 1 that is communicating with a process on \B in CPU 1 will use
the line handler configured on CPU 1. If another process on \A in CPU 1 is started that
also communicates with a process on \B in CPU 1, the same line handler would be
used (the one on CPU 1). This is because of the CPU matching rules.
If no line handler directly connects the two CPUs, a best match is done. A process on
\A in CPU 0 that is communicating with a process on \B in CPU 3 will use the line
handler configured on CPU 3. That is the line handler that has the best match—the
remote Rhinelander CPU matches the destination process CPU.
Load Factor Balancing
If there are no matching CPUs, then the load would be distributed based on the load
factor of the paths in the superpath.
If a process on \A in CPU 0 is communicating with a process on \B in CPU 2, the line
handler chosen is based on the load factor of the two lines.
Once the CPU pair has been established, that line handler is used for all
communication between the two CPUs. In an example of CPU 0 to CPU 2 and
assuming that the line handler in CPU 3 is the one chosen, all traffic from CPU 0 to
CPU 2 uses the line handler in CPU 3.
Pair Count Balancing
If the loads are fairly close, the number of CPU pairs using the paths in a superpath is
looked at in determining the connection.
Figure 20-4 depicts the loading for systems that are direct neighbors and are
connected with a superpath, plus connections for non-neighbors:
Note. The selection algorithm is such that the more loaded line can still be chosen. When a
new connection is being established, the selection algorithm not only looks at the load factor,
but also checks to see if this path has been chosen recently. A loaded path can still be chosen
as the one for a new connection. This way, a single line that looks unused at the time won't get
all of the new connections assigned to it, but they will be distributed over the superpath.