runtime,runtime/metrics: add heap goal and GC cycle metrics

This change adds three new metrics: the heap goal, GC cycle count, and
forced GC count. These metrics are identical to their MemStats
counterparts.

For #37112.

Change-Id: I5a5e8dd550c0d646e5dcdbdf38274895e27cdd88
Reviewed-on: https://go-review.googlesource.com/c/go/+/247044
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/runtime/metrics.go

@@ -7,6 +7,7 @@ package runtime
 // Metrics implementation exported to runtime/metrics.
 
 import (
+	"runtime/internal/atomic"
 	"unsafe"
 )
 
@@ -38,6 +39,34 @@ func initMetrics() {
 		return
 	}
 	metrics = map[string]metricData{
+		"/gc/cycles/automatic:gc-cycles": {
+			deps: makeStatDepSet(sysStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.sysStats.gcCyclesDone - in.sysStats.gcCyclesForced
+			},
+		},
+		"/gc/cycles/forced:gc-cycles": {
+			deps: makeStatDepSet(sysStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.sysStats.gcCyclesForced
+			},
+		},
+		"/gc/cycles/total:gc-cycles": {
+			deps: makeStatDepSet(sysStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.sysStats.gcCyclesDone
+			},
+		},
+		"/gc/heap/goal:bytes": {
+			deps: makeStatDepSet(sysStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.sysStats.heapGoal
+			},
+		},
 		"/gc/heap/objects:objects": {
 			deps: makeStatDepSet(heapStatsDep),
 			compute: func(in *statAggregate, out *metricValue) {
@@ -256,6 +285,9 @@ type sysStatsAggregate struct {
 	buckHashSys    uint64
 	gcMiscSys      uint64
 	otherSys       uint64
+	heapGoal       uint64
+	gcCyclesDone   uint64
+	gcCyclesForced uint64
 }
 
 // compute populates the sysStatsAggregate with values from the runtime.
@@ -264,6 +296,9 @@ func (a *sysStatsAggregate) compute() {
 	a.buckHashSys = memstats.buckhash_sys.load()
 	a.gcMiscSys = memstats.gcMiscSys.load()
 	a.otherSys = memstats.other_sys.load()
+	a.heapGoal = atomic.Load64(&memstats.next_gc)
+	a.gcCyclesDone = uint64(memstats.numgc)
+	a.gcCyclesForced = uint64(memstats.numforcedgc)
 
 	systemstack(func() {
 		lock(&mheap_.lock)

src/runtime/metrics/description.go

@@ -50,6 +50,29 @@ type Description struct {
 // The English language descriptions below must be kept in sync with the
 // descriptions of each metric in doc.go.
 var allDesc = []Description{
+	{
+		Name:        "/gc/cycles/automatic:gc-cycles",
+		Description: "Count of completed GC cycles generated by the Go runtime.",
+		Kind:        KindUint64,
+		Cumulative:  true,
+	},
+	{
+		Name:        "/gc/cycles/forced:gc-cycles",
+		Description: "Count of completed forced GC cycles.",
+		Kind:        KindUint64,
+		Cumulative:  true,
+	},
+	{
+		Name:        "/gc/cycles/total:gc-cycles",
+		Description: "Count of all completed GC cycles.",
+		Kind:        KindUint64,
+		Cumulative:  true,
+	},
+	{
+		Name:        "/gc/heap/goal:bytes",
+		Description: "Heap size target for the end of the GC cycle.",
+		Kind:        KindUint64,
+	},
 	{
 		Name:        "/gc/heap/objects:objects",
 		Description: "Number of objects, live or unswept, occupying heap memory.",

src/runtime/metrics/doc.go

@@ -44,6 +44,18 @@ the documentation of the Name field of the Description struct.
 
 Supported metrics
 
+	/gc/cycles/automatic:gc-cycles
+		Count of completed GC cycles generated by the Go runtime.
+
+	/gc/cycles/forced:gc-cycles
+		Count of completed forced GC cycles.
+
+	/gc/cycles/total:gc-cycles
+		Count of all completed GC cycles.
+
+	/gc/heap/goal:bytes
+		Heap size target for the end of the GC cycle.
+
 	/gc/heap/objects:objects
 		Number of objects, live or unswept, occupying heap memory.
 

src/runtime/metrics_test.go

@@ -72,6 +72,14 @@ func TestReadMetrics(t *testing.T) {
 			checkUint64(t, name, samples[i].Value.Uint64(), mstats.Sys)
 		case "/gc/heap/objects:objects":
 			checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapObjects)
+		case "/gc/heap/goal:bytes":
+			checkUint64(t, name, samples[i].Value.Uint64(), mstats.NextGC)
+		case "/gc/cycles/automatic:gc-cycles":
+			checkUint64(t, name, samples[i].Value.Uint64(), uint64(mstats.NumGC-mstats.NumForcedGC))
+		case "/gc/cycles/forced:gc-cycles":
+			checkUint64(t, name, samples[i].Value.Uint64(), uint64(mstats.NumForcedGC))
+		case "/gc/cycles/total:gc-cycles":
+			checkUint64(t, name, samples[i].Value.Uint64(), uint64(mstats.NumGC))
 		}
 	}
 }