[LU-12289] Route with fault remote device selected on separated IB subnet

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Affects Version/s: Lustre 2.12.1

Epic/Theme

lnet

• Severity: 3
• Assignee: Tatsushi Takamura
• Reporter: Tatsushi Takamura

Description

LNet MultiRail selects routes from local to remote in order.
Local device is detemined in round-robin fashion,
so even if Health value of a remote device(A) is smaller than another remote device(B),
a local device(A) which is the peer of the remote device(A) may be selected.
If device(A) and device(B) are on different subnets, a failure route will be selected.

          Subnet1     Subnet2

           (DOWN)  |
    REMOTE  IB(A)  |   IB(B)
            ↑      |
            x      |
            |      |
     LOCAL  IB(A)  |   IB(B)

local device is selected in round-robin fashion regardless of remote side device status

We modify the finding best local device algorithm as follows,

1. get the maximum health value of remote device
2. if the value is smaller than the best health value, don't use this device
3. if the value is bigger than the best health value, update the best device
4. if the value is identical with the best value, update the best device by conventional way
5. update the best health value

Issue Links

• is related to: LU-13025 LNet Health: Peer net health not considered