From b0e5d64bd7ffec0c11550fd77f2f92dff6a4c90f Mon Sep 17 00:00:00 2001
From: Amir Alavi <amiralavi7@gmail.com>
Date: Tue, 13 Jul 2021 22:41:23 -0400
Subject: [PATCH] TopologySpreadConstraint: advance above avg index when at
 ideal average when balancing domains

---
 .../strategies/topologyspreadconstraint.go    |  2 +-
 .../topologyspreadconstraint_test.go          | 56 +++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/pkg/descheduler/strategies/topologyspreadconstraint.go b/pkg/descheduler/strategies/topologyspreadconstraint.go
index b5d41556c5..36c857a6b1 100644
--- a/pkg/descheduler/strategies/topologyspreadconstraint.go
+++ b/pkg/descheduler/strategies/topologyspreadconstraint.go
@@ -281,7 +281,7 @@ func balanceDomains(
 	j := len(sortedDomains) - 1
 	for i < j {
 		// if j has no more to give without falling below the ideal average, move to next aboveAvg
-		if float64(len(sortedDomains[j].pods)) < idealAvg {
+		if float64(len(sortedDomains[j].pods)) <= idealAvg {
 			j--
 		}
 
diff --git a/pkg/descheduler/strategies/topologyspreadconstraint_test.go b/pkg/descheduler/strategies/topologyspreadconstraint_test.go
index d1b608be45..cc4c89dd85 100644
--- a/pkg/descheduler/strategies/topologyspreadconstraint_test.go
+++ b/pkg/descheduler/strategies/topologyspreadconstraint_test.go
@@ -588,6 +588,62 @@ func TestTopologySpreadConstraint(t *testing.T) {
 			strategy:             api.DeschedulerStrategy{Params: &api.StrategyParameters{IncludeSoftConstraints: true}},
 			namespaces:           []string{"ns1"},
 		},
+		{
+			name: "3 domains size [8 7 0], maxSkew=1, should move 5 to get [5 5 5]",
+			nodes: []*v1.Node{
+				test.BuildTestNode("n1", 2000, 3000, 10, func(n *v1.Node) { n.Labels["zone"] = "zoneA" }),
+				test.BuildTestNode("n2", 2000, 3000, 10, func(n *v1.Node) { n.Labels["zone"] = "zoneB" }),
+				test.BuildTestNode("n3", 2000, 3000, 10, func(n *v1.Node) { n.Labels["zone"] = "zoneC" }),
+			},
+			pods: createTestPods([]testPodList{
+				{
+					count:       8,
+					node:        "n1",
+					labels:      map[string]string{"foo": "bar"},
+					constraints: getDefaultTopologyConstraints(1),
+				},
+				{
+					count:       7,
+					node:        "n2",
+					labels:      map[string]string{"foo": "bar"},
+					constraints: getDefaultTopologyConstraints(1),
+				},
+			}),
+			expectedEvictedCount: 5,
+			strategy:             api.DeschedulerStrategy{},
+			namespaces:           []string{"ns1"},
+		},
+		{
+			name: "3 domains size [5 5 5], maxSkew=1, should move 0 to retain [5 5 5]",
+			nodes: []*v1.Node{
+				test.BuildTestNode("n1", 2000, 3000, 10, func(n *v1.Node) { n.Labels["zone"] = "zoneA" }),
+				test.BuildTestNode("n2", 2000, 3000, 10, func(n *v1.Node) { n.Labels["zone"] = "zoneB" }),
+				test.BuildTestNode("n3", 2000, 3000, 10, func(n *v1.Node) { n.Labels["zone"] = "zoneC" }),
+			},
+			pods: createTestPods([]testPodList{
+				{
+					count:       5,
+					node:        "n1",
+					labels:      map[string]string{"foo": "bar"},
+					constraints: getDefaultTopologyConstraints(1),
+				},
+				{
+					count:       5,
+					node:        "n2",
+					labels:      map[string]string{"foo": "bar"},
+					constraints: getDefaultTopologyConstraints(1),
+				},
+				{
+					count:       5,
+					node:        "n3",
+					labels:      map[string]string{"foo": "bar"},
+					constraints: getDefaultTopologyConstraints(1),
+				},
+			}),
+			expectedEvictedCount: 0,
+			strategy:             api.DeschedulerStrategy{},
+			namespaces:           []string{"ns1"},
+		},
 		{
 			name: "2 domains, sizes [2,0], maxSkew=1, move 1 pod since pod tolerates the node with taint",
 			nodes: []*v1.Node{