User Manual

Rev 2.2-1.0.1
Mellanox Technologies
179
8.5.3.1 UPDN Algorithm Usage
Activation through OpenSM
• Use '-R updn' option (instead of old '-u') to activate the UPDN algorithm.
• Use '-a <root_guid_file>' for adding an UPDN guid file that contains the root nodes for
ranking. If the `-a' option is not used, OpenSM uses its auto-detect root nodes algo
-
rithm.
Notes on the guid list file:
• A valid guid file specifies one guid in each line. Lines with an invalid format will be
discarded
• The user should specify the root switch guids
8.5.4 Fat-tree Routing Algorithm
The fat-tree algorithm optimizes routing for "shift" communication pattern. It should be chosen if
a subnet is a symmetrical or almost symmetrical fat-tree of various types. It supports not just
K-ary-N-Trees, by handling for non-constant K, cases where not all leafs (CAs) are present, any
Constant Bisectional Ratio (CBB )ratio. As in UPDN, fat-tree also prevents credit-loop-dead
-
locks.
If the root guid file is not provided ('-a' or '--root_guid_file' options), the topology has to
be pure fat-tree that complies with the following rules:
• Tree rank should be between two and eight (inclusively)
• Switches of the same rank should have the same number of UP-going port groups
1
,
unless they are root switches, in which case the shouldn't have UP-going ports at all.
• Switches of the same rank should have the same number of DOWN-going port groups,
unless they are leaf switches.
• Switches of the same rank should have the same number of ports in each UP-going port
group.
• Switches of the same rank should have the same number of ports in each DOWN-going
port group.
• All the CAs have to be at the same tree level (rank).
If the root guid file is provided, the topology does not have to be pure fat-tree, and it should only
comply with the following rules:
• Tree rank should be between two and eight (inclusively)
• All the Compute Nodes
2
have to be at the same tree level (rank). Note that non-compute
node CAs are allowed here to be at different tree ranks.
Topologies that do not comply cause a fallback to min hop routing. Note that this can also
occur on link failures which cause the topology to no longer be a “pure” fat-tree.
Note that although fat-tree algorithm supports trees with non-integer CBB ratio, the routing
will not be as balanced as in case of integer CBB ratio. In addition to this, although the algo
-
rithm allows leaf switches to have any number of CAs, the closer the tree is to be fully popu-
lated, the more effective the "shift" communication pattern will be. In general, even if the
1. Ports that are connected to the same remote switch are referenced as ‘port group’
2. List of compute nodes (CNs) can be specified by ‘-u’ or ‘--cn_guid_file’ OpenSM options.