User Manual

Rev 2.1-1.0.6
Mellanox Technologies
159
8.5.6 DOR Routing Algorithm
The Dimension Order Routing algorithm is based on the Min Hop algorithm and so uses short-
est paths. Instead of spreading traffic out across different paths with the same shortest distance, it
chooses among the available shortest paths based on an ordering of dimensions. Each port must
be consistently cabled to represent a hypercube dimension or a mesh dimension. Paths are
grown from a destination back to a source using the lowest dimension (port) of available paths
at each step. This provides the ordering necessary to avoid deadlock. When there are multiple
links between any two switches, they still represent only one dimension and traffic is balanced
across them unless port equalization is turned off. In the case of hypercubes, the same port must
be used throughout the fabric to represent the hypercube dimension and match on both ends
of the cable. In the case of meshes, the dimension should consistently use the same pair of
ports, one port on one end of the cable, and the other port on the other end, continuing along the
mesh dimension.
Use ‘-R dor’ option to activate the DOR algorithm.
8.5.7 Torus-2QoS Routing Algorithm
Torus-2QoS is a routing algorithm designed for large-scale 2D/3D torus fabrics. The torus-2QoS
routing engine can provide the following functionality on a 2D/3D torus:
• Free of credit loops routing
• Two levels of QoS, assuming switches support 8 data VLs
• Ability to route around a single failed switch, and/or multiple failed links, without:
• introducing credit loops
• changing path SL values
• Very short run times, with good scaling properties as fabric size increases
8.5.7.1 Unicast Routing
sl = 0;
for (d = 0; d < torus_dimensions; d++)
/* path_crosses_dateline(d) returns 0 or 1 */
sl |= path_crosses_dateline(d) << d;
for (sl = 0; sl < 16; sl ++)
/* cdir(port) reports which torus coordinate direction a switch port
* "points" in, and returns 0, 1, or 2 */
sl2vl(iport,oport,sl) = 0x1 & (sl >> cdir(oport));
Torus-2QoS is a DOR-based algorithm that avoids deadlocks that would otherwise occur in a
torus using the concept of a dateline for each torus dimension. It encodes into a path SL which
datelines the path crosses as follows:
For a 3D torus, that leaves one SL bit free, which torus-2QoS uses to implement two QoS levels.
T
orus-2QoS also makes use of the output port dependence of switch SL2VL maps to encode into
one VL bit the information encoded in three SL bits. It computes in which torus coordinate direc-
tion each inter-switch link "points", and writes SL2VL maps for such ports as follows: