Add metrics to equivalence cache.

This adds counters to equiv. cache reads & writes. Reads are labeled by
hit/miss, while writes are labeled to indicate whether the write was
discarded.

This will give us visibility into,
- hit rate of cache reads
- ratio of reads to writes
- rate of discarded writes

pkg/scheduler/core/equivalence/BUILD

@@ -9,6 +9,7 @@ go_library(
         "//pkg/scheduler/algorithm:go_default_library",
         "//pkg/scheduler/algorithm/predicates:go_default_library",
         "//pkg/scheduler/cache:go_default_library",
+        "//pkg/scheduler/metrics:go_default_library",
         "//pkg/util/hash:go_default_library",
         "//staging/src/k8s.io/api/core/v1:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/util/sets:go_default_library",

pkg/scheduler/core/equivalence/eqivalence.go

@@ -23,6 +23,8 @@ import (
 	"hash/fnv"
 	"sync"
 
+	"k8s.io/kubernetes/pkg/scheduler/metrics"
+
 	"k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/kubernetes/pkg/scheduler/algorithm"
@@ -244,10 +246,12 @@ func (n *NodeCache) updateResult(
 ) {
 	if nodeInfo == nil || nodeInfo.Node() == nil {
 		// This may happen during tests.
+		metrics.EquivalenceCacheWrites.WithLabelValues("discarded_bad_node").Inc()
 		return
 	}
 	// Skip update if NodeInfo is stale.
 	if !cache.IsUpToDate(nodeInfo) {
+		metrics.EquivalenceCacheWrites.WithLabelValues("discarded_stale").Inc()
 		return
 	}
 
@@ -282,6 +286,11 @@ func (n *NodeCache) lookupResult(
 	n.mu.RLock()
 	defer n.mu.RUnlock()
 	value, ok = n.cache[predicateKey][equivalenceHash]
+	if ok {
+		metrics.EquivalenceCacheHits.Inc()
+	} else {
+		metrics.EquivalenceCacheMisses.Inc()
+	}
 	return value, ok
 }
 

pkg/scheduler/metrics/metrics.go

@@ -117,6 +117,23 @@ var (
 			Name:      "total_preemption_attempts",
 			Help:      "Total preemption attempts in the cluster till now",
 		})
+
+	equivalenceCacheLookups = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Subsystem: SchedulerSubsystem,
+			Name:      "equiv_cache_lookups_total",
+			Help:      "Total number of equivalence cache lookups, by whether or not a cache entry was found",
+		}, []string{"result"})
+	EquivalenceCacheHits   = equivalenceCacheLookups.With(prometheus.Labels{"result": "hit"})
+	EquivalenceCacheMisses = equivalenceCacheLookups.With(prometheus.Labels{"result": "miss"})
+
+	EquivalenceCacheWrites = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Subsystem: SchedulerSubsystem,
+			Name:      "equiv_cache_writes",
+			Help:      "Total number of equivalence cache writes, by result",
+		}, []string{"result"})
+
 	metricsList = []prometheus.Collector{
 		SchedulingLatency,
 		E2eSchedulingLatency,
@@ -127,6 +144,8 @@ var (
 		SchedulingAlgorithmPremptionEvaluationDuration,
 		PreemptionVictims,
 		PreemptionAttempts,
+		equivalenceCacheLookups,
+		EquivalenceCacheWrites,
 	}
 )