fit: further optimize the selection of witness rule candidates (#6148)

close #5568, ref #5568

fit: further optimize the selection of witness rule candidates

Signed-off-by: Wenbo Zhang <ethercflow@gmail.com>

Co-authored-by: Ti Chi Robot <ti-community-prow-bot@tidb.io>

pkg/schedule/placement/fit.go

@@ -119,6 +119,7 @@ type RuleFit struct {
 	// IsolationScore indicates at which level of labeling these Peers are
 	// isolated. A larger value is better.
 	IsolationScore float64 `json:"isolation-score"`
+	WitnessScore   int     `json:"witness-score"`
 	// stores is the stores that the peers are placed in.
 	stores []*core.StoreInfo
 }
@@ -151,6 +152,10 @@ func compareRuleFit(a, b *RuleFit) int {
 		return -1
 	case a.IsolationScore > b.IsolationScore:
 		return 1
+	case a.WitnessScore > b.WitnessScore:
+		return -1
+	case a.WitnessScore < b.WitnessScore:
+		return 1
 	default:
 		return 0
 	}
@@ -345,7 +350,7 @@ func (w *fitWorker) updateOrphanPeers(index int) {
 }
 
 func newRuleFit(rule *Rule, peers []*fitPeer, supportWitness bool) *RuleFit {
-	rf := &RuleFit{Rule: rule, IsolationScore: isolationScore(peers, rule.LocationLabels)}
+	rf := &RuleFit{Rule: rule, IsolationScore: isolationScore(peers, rule.LocationLabels), WitnessScore: witnessScore(peers, supportWitness && rule.IsWitness)}
 	for _, p := range peers {
 		rf.Peers = append(rf.Peers, p.Peer)
 		rf.stores = append(rf.stores, p.store)
@@ -441,3 +446,14 @@ func stateScore(region *core.RegionInfo, peerID uint64) int {
 		return 2
 	}
 }
+
+func witnessScore(peers []*fitPeer, fitWitness bool) int {
+	var score int
+	if !fitWitness || len(peers) == 0 {
+		return 0
+	}
+	for _, p := range peers {
+		score += p.store.GetWitnessCount()
+	}
+	return score
+}