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

Related — Fri, 16 Oct 2020 06:21:54 +0000

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,

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

Whamcloud Community JIRA

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