IBM RS/6000 SP, Problem Determination Manual

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but not by 50%. Testing has shown that the expected performance reduction is
usually within the 10 to 15% range. Much will depend on the specifics of the
particular system, and the type of network traffic generated on the switch.
With the High Performance Switch, the IP protocol only uses one path at a time
3
,
so the impact is likely to be less. There is still a scope of packet contention in a
busy switch network, because if a path is blocked, then only one alternative
exists. The user space message passing mode protocol is able to use multiple
paths, and so the performance impact may be greater depending on the type of
network traffic.
This protocol is used by parallel programs that require a high bandwidth and low
latency for their message passing. In addition, the impact of losing one of the
internal routes on the switch board becomes far more severe in the 8-way
partition, because only one path will be available for communicating between
nodes on different switch chips. The chance of experiencing packet contention is
increased considerably, which could have a major impact on performance. In an
unpartitioned system, the effect of losing an internal link or route would be
minimal and the switch could run indefinitely until an opportunity is available to
carry out maintenance.
Similar considerations can be applied to the 12-way partition, but the impact is
minimal because 3 out of the 4 routes are still available.
Based on the 8_8 example previously given, the topology files shown in
Figure 60 illustrate how the routes have been deleted.
# Node connections in frame L01 to switch 1 in L01
s 15 3 tb0 0 0
E01-S17-BH-J18 to E01-N1
s 15 2 tb0 1 0 E01-S17-BH-J16 to E01-N2
s 15 1 tb0 4 0 E01-S17-BH-J14 to E01-N5
s 15 0 tb0 5 0 E01-S17-BH-J12 to E01-N6
s 14 3 tb0 8 0 E01-S17-BH-J10 to E01-N9
s 14 2 tb0 9 0 E01-S17-BH-J8 to Exx-Nxx
s 14 1 tb0 12 0 E01-S17-BH-J6 to E01-N13
s 14 0 tb0 13 0 E01-S17-BH-J4 to Exx-Nxx
# On board connections between switch chips on switch 1 in Frame L01
s 14 7
s 13 4 E01-S17-SC
s 14 6 s 12 4 E01-S17-SC
s 15 7 s 13 5 E01-S17-SC
s 15 6 s 12 5 E01-S17-SC
Figure 60. Insert of Topology File for the First 8-Way Partition
Node connections are present only for the nodes in the partition, and there are
only 4 links present for the onboard switch chip connections. When diagnosing
configuration problems, check that the correct topology file is being used for the
partition you are having difficulty with. The topology files are stored in the SDR
directory:
/spdata/sys1/sdr/partitions/<IP alias address>/files
3
With the new SP Switch this is no longer the case; IP can use multiple paths.
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SP PD Guide