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Use maxSkew in PodTopologySpread scoring as tolerance to skew

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This new approach results in better spreading for small number of pods, while still giving meaning to the maxSkew parameter.

Signed-off-by: Aldo Culquicondor <acondor@google.com>
This commit is contained in:
Aldo Culquicondor 2020-06-08 16:25:32 -04:00
parent a36b9a9922
commit d353cc1532
2 changed files with 15 additions and 21 deletions
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18
pkg/scheduler/framework/plugins/podtopologyspread/scoring.go
View File

@ -200,8 +200,7 @@ func (pl *PodTopologySpread) Score(ctx context.Context, cycleState *framework.Cy
pair := topologyPair{key: c.TopologyKey, value: tpVal}
cnt = *s.TopologyPairToPodCounts[pair]
}
cnt = adjustForMaxSkew(cnt, int64(c.MaxSkew))
score += float64(cnt) * s.TopologyNormalizingWeight[i]
score += scoreForCount(cnt, c.MaxSkew, s.TopologyNormalizingWeight[i])
}
}
return int64(score), nil
@ -287,13 +286,10 @@ func topologyNormalizingWeight(size int) float64 {
return math.Log(float64(size + 2))
}
// adjustForMaxSkew adjusts the number of matching pods in a topology domain
// using the constraint's maxSkew.
// Topology domains with less than maxSkew number of pods are considered to have
// the same priority.
func adjustForMaxSkew(cnt, maxSkew int64) int64 {
if cnt < maxSkew {
return maxSkew - 1
}
return cnt
// scoreForCount calculates the score based on number of matching pods in a
// topology domain, the constraint's maxSkew and the topology weight.
// `maxSkew-1` is added to the score so that differences between topology
// domains get watered down, controlling the tolerance of the score to skews.
func scoreForCount(cnt int64, maxSkew int32, tpWeight float64) float64 {
return float64(cnt)*tpWeight + float64(maxSkew-1)
}

18
pkg/scheduler/framework/plugins/podtopologyspread/scoring_test.go
View File

@ -315,12 +315,11 @@ func TestPodTopologySpreadScore(t *testing.T) {
},
},
{
// matching pods spread as 2/1/0/3.
// With maxSkew=2, counts change internally to 2/1/1/3.
name: "one constraint on node, all 4 nodes are candidates, maxSkew=2",
pod: st.MakePod().Name("p").Label("foo", "").
SpreadConstraint(2, v1.LabelHostname, v1.ScheduleAnyway, st.MakeLabelSelector().Exists("foo").Obj()).
Obj(),
// matching pods spread as 2/1/0/3.
existingPods: []*v1.Pod{
st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
@ -337,20 +336,19 @@ func TestPodTopologySpreadScore(t *testing.T) {
},
failedNodes: []*v1.Node{},
want: []framework.NodeScore{
{Name: "node-a", Score: 60}, // +20, compared to maxSkew=1
{Name: "node-b", Score: 100}, // +20, compared to maxSkew=1
{Name: "node-a", Score: 50}, // +10, compared to maxSkew=1
{Name: "node-b", Score: 83}, // +3, compared to maxSkew=1
{Name: "node-c", Score: 100},
{Name: "node-d", Score: 20}, // +20, compared to maxSkew=1
{Name: "node-d", Score: 16}, // +16, compared to maxSkew=1
},
},
{
// matching pods spread as 4/3/2/1.
// With maxSkew=3, counts change internally to 4/3/2/2.
name: "one constraint on node, all 4 nodes are candidates, maxSkew=3",
pod: st.MakePod().Name("p").Label("foo", "").
SpreadConstraint(3, v1.LabelHostname, v1.ScheduleAnyway, st.MakeLabelSelector().Exists("foo").Obj()).
Obj(),
existingPods: []*v1.Pod{
// matching pods spread as 4/3/2/1.
st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
st.MakePod().Name("p-a3").Node("node-a").Label("foo", "").Obj(),
@ -370,9 +368,9 @@ func TestPodTopologySpreadScore(t *testing.T) {
},
failedNodes: []*v1.Node{},
want: []framework.NodeScore{
{Name: "node-a", Score: 42}, // +28 compared to maxSkew=1
{Name: "node-b", Score: 71}, // +29 compared to maxSkew=1
{Name: "node-c", Score: 100}, // +29 compared to maxSkew=1
{Name: "node-a", Score: 33}, // +19 compared to maxSkew=1
{Name: "node-b", Score: 55}, // +13 compared to maxSkew=1
{Name: "node-c", Score: 77}, // +6 compared to maxSkew=1
{Name: "node-d", Score: 100},
},
},