...
UDSP application and Selection Priority
...
It is important to clarify the order UDSP rules are applied versus the selection priority. These two are distinct concepts which need to be kept separate for the simplicity of the design.
The order UDSPs are applied is on first matching rule case. When there are a set of policies of the same type, which apply to the same LNet construct, only the first policy on the list of policies is applied on the matching LNet construct. To make this concept distinct from the selection priority concept, it shall be referred to as UDSP Application Order.
The Selection Priority, is the Policy Action part of the UDSP as described earlier. This Selection Priority only applies to the LNet construct on which the UDSP is being instantiated and is not related to the UDSP Application Order. The Selection Priority of an LNet construct is what the Selection Algorithm uses as one of the criteria for selecting the LNet construct under examination when sending a message.
UDSP Policy Interactions
Once a UDSP policy is instantiated on an LNet construct, the UDSP action becomes part of the LNet construct. When the selection algorithm is running on per message send case, the policy action takes effect. To give a more concrete example, let's say the admin applies a policy which gives the highest Selection Priority for o2ib0 local network. This policy action translates to the local network selection priority field set to 0, which is the highest priority. When the selection algorithm runs it checks the priorities of all local networks and selects o2ib0 since it has the highest Selection priority.
Policy Actions however, do not exist in a vacuum and must integrate with the rest of the Selection Criteria used by the selection algorithm. For more details on the selection algorithm, please refer to the initial Multi-Rail HLD.
There is one particular rule which all UDSPs will adhere to, Health will always trump UDSPs. The selection algorithm will always select the healthiest interface to send from or to send to irregardless if there is another network and/or interface which has a higher user assigned Selection Priority. The following diagram attempts to give an overview of the selection algorithm, but the HLD linked above is the best place to get more details, as this HLD concentrates on the UDSP design and does not intend to rehash all the details of the selection algorithm. Only the details needed to explain the UDSP functionality.
| Gliffy Diagram | ||||||
|---|---|---|---|---|---|---|
|
UDSP Rules Types
Outlined below are the UDSP rule types
...