Introduce a metric measuring heterogeneity of binpacking

Binpacking estimator has optimizations to allow homogeneous workloads to
be efficiently processed together. Measuring heterogeneity is required
to gain insight into cases when these optimizations matter and when they
don't.

cluster-autoscaler/estimator/binpacking_estimator.go

@@ -18,9 +18,11 @@ package estimator
 
 import (
 	"fmt"
+	"strconv"
 
 	apiv1 "k8s.io/api/core/v1"
 	"k8s.io/autoscaler/cluster-autoscaler/cloudprovider"
+	"k8s.io/autoscaler/cluster-autoscaler/metrics"
 	core_utils "k8s.io/autoscaler/cluster-autoscaler/simulator"
 	"k8s.io/autoscaler/cluster-autoscaler/simulator/clustersnapshot"
 	"k8s.io/autoscaler/cluster-autoscaler/simulator/framework"
@@ -93,6 +95,7 @@ func (e *BinpackingNodeEstimator) Estimate(
 	nodeTemplate *framework.NodeInfo,
 	nodeGroup cloudprovider.NodeGroup,
 ) (int, []*apiv1.Pod) {
+	observeBinpackingHeterogeneity(podsEquivalenceGroups, nodeTemplate)
 
 	e.limiter.StartEstimation(podsEquivalenceGroups, nodeGroup, e.context)
 	defer e.limiter.EndEstimation()
@@ -231,3 +234,31 @@ func (e *BinpackingNodeEstimator) addNewNodeToSnapshot(
 	estimationState.newNodeNames[estimationState.lastNodeName] = true
 	return nil
 }
+
+func observeBinpackingHeterogeneity(podsEquivalenceGroups []PodEquivalenceGroup, nodeTemplate *framework.NodeInfo) {
+	node := nodeTemplate.Node()
+	var instanceType, cpuCount string
+	if node != nil {
+		if node.Labels != nil {
+			instanceType = node.Labels[apiv1.LabelInstanceTypeStable]
+		}
+		cpuCount = node.Status.Capacity.Cpu().String()
+	}
+	namespaces := make(map[string]bool)
+	for _, peg := range podsEquivalenceGroups {
+		e := peg.Exemplar()
+		if e != nil {
+			namespaces[e.Namespace] = true
+		}
+	}
+	// Quantize # of namespaces to limit metric cardinality.
+	nsCountBucket := ""
+	if len(namespaces) <= 5 {
+		nsCountBucket = strconv.Itoa(len(namespaces))
+	} else if len(namespaces) <= 10 {
+		nsCountBucket = "6-10"
+	} else {
+		nsCountBucket = "11+"
+	}
+	metrics.ObserveBinpackingHeterogeneity(instanceType, cpuCount, nsCountBucket, len(podsEquivalenceGroups))
+}

cluster-autoscaler/metrics/metrics.go

@@ -418,6 +418,15 @@ var (
 			Help:      "Number of migs where instance count according to InstanceGroupManagers.List() differs from the results of Instances.List(). This can happen when some instances are abandoned or a user edits instance 'created-by' metadata.",
 		},
 	)
+
+	binpackingHeterogeneity = k8smetrics.NewHistogramVec(
+		&k8smetrics.HistogramOpts{
+			Namespace: caNamespace,
+			Name:      "binpacking_heterogeneity",
+			Help:      "Number of groups of equivalent pods being processed as a part of the same binpacking simulation.",
+			Buckets:   []float64{1, 2, 4, 6, 10},
+		}, []string{"instance_type", "cpu_count", "namespace_count"},
+	)
 )
 
 // RegisterAll registers all metrics.
@@ -453,6 +462,7 @@ func RegisterAll(emitPerNodeGroupMetrics bool) {
 	legacyregistry.MustRegister(pendingNodeDeletions)
 	legacyregistry.MustRegister(nodeTaintsCount)
 	legacyregistry.MustRegister(inconsistentInstancesMigsCount)
+	legacyregistry.MustRegister(binpackingHeterogeneity)
 
 	if emitPerNodeGroupMetrics {
 		legacyregistry.MustRegister(nodesGroupMinNodes)
@@ -736,3 +746,9 @@ func ObserveNodeTaintsCount(taintType string, count float64) {
 func UpdateInconsistentInstancesMigsCount(migCount int) {
 	inconsistentInstancesMigsCount.Set(float64(migCount))
 }
+
+// ObserveBinpackingHeterogeneity records the number of pod equivalence groups
+// considered in a single binpacking estimation.
+func ObserveBinpackingHeterogeneity(instanceType, cpuCount, namespaceCount string, pegCount int) {
+	binpackingHeterogeneity.WithLabelValues(instanceType, cpuCount, namespaceCount).Observe(float64(pegCount))
+}