[LU-12288] Preferred flag of route selection policy does not work

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Affects Version/s: Lustre 2.12.1
• Severity: 3
• Assignee: Tatsushi Takamura
• Reporter: Tatsushi Takamura

Description

Route selection is detemined according to circumstances(Preferred, Health Value, Credits and Seq Number) and Preferred is top priority.

        /*
         * Look at the peer NIs for the destination peer that connect
         * to the chosen net. If a peer_ni is preferred when using the
         * best_ni to communicate, we use that one. If there is no
         * preferred peer_ni, or there are multiple preferred peer_ni,
         * the available transmit credits are used. If the transmit
         * credits are equal, we round-robin over the peer_ni.
         */

But, If there are more than 2 peers and the first peer is Preffered, there are cases where the Preffered peer(the first one) is not selected(Preffered flag is ignored).
Also, there are no need to set Preferred flag on when recovery.

lnet_select_peer_ni()

    /* pick the healthiest peer ni */
    if (lpni_healthv < best_lpni_healthv) {
        continue;
    } else if (lpni_healthv > best_lpni_healthv) {
        best_lpni_healthv = lpni_healthv; // peer1(supporse ni_is_pref), but preferred flag not be set
    /* if this is a preferred peer use it */
    } else if (!preferred && ni_is_pref) {
            preferred = true;            
    } else if (preferred && !ni_is_pref) { 
            continue;
    } else if (lpni->lpni_txcredits < best_lpni_credits) { // peer2 is judged by another metrics

We fixed that route selection is in the following order.

1. Preferred
2. Health Value
3. Credits
4. Seq Number