tsweb/varz: export GC CPU fraction gauge

We were missing this metric, but it can be important for some workloads. Varz memstats output allocation cost reduced from 30 allocs per invocation to 1 alloc per invocation. Updates tailscale/corp#28033 Signed-off-by: James Tucker <james@tailscale.com> Co-authored-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2025-04-28 09:04:02 -07:00
parent 189e03e741
commit b95e8bf4a1
5 changed files with 128 additions and 17 deletions
@@ -4,14 +4,17 @@
 package varz

 import (
+	"bytes"
 	"expvar"
 	"net/http/httptest"
 	"reflect"
+	"runtime"
 	"strings"
 	"testing"

 	"tailscale.com/metrics"
 	"tailscale.com/tstest"
+	"tailscale.com/util/racebuild"
 	"tailscale.com/version"
 )

@@ -418,3 +421,75 @@ func TestVarzHandlerSorting(t *testing.T) {
 		}
 	}
 }
+
+func TestWriteMemestats(t *testing.T) {
+	memstats := &runtime.MemStats{
+		Alloc:        1,
+		TotalAlloc:   2,
+		Sys:          3,
+		Lookups:      4,
+		Mallocs:      5,
+		Frees:        6,
+		HeapAlloc:    7,
+		HeapSys:      8,
+		HeapIdle:     9,
+		HeapInuse:    10,
+		HeapReleased: 11,
+		HeapObjects:  12,
+		StackInuse:   13,
+		StackSys:     14,
+		MSpanInuse:   15,
+		MSpanSys:     16,
+		MCacheInuse:  17,
+		MCacheSys:    18,
+		BuckHashSys:  19,
+		GCSys:        20,
+		OtherSys:     21,
+		NextGC:       22,
+		LastGC:       23,
+		PauseTotalNs: 24,
+		// PauseNs:       [256]int64{},
+		NumGC:         26,
+		NumForcedGC:   27,
+		GCCPUFraction: 0.28,
+	}
+
+	var buf bytes.Buffer
+	writeMemstats(&buf, memstats)
+	lines := strings.Split(buf.String(), "\n")
+
+	checkFor := func(name, typ, value string) {
+		var foundType, foundValue bool
+		for _, line := range lines {
+			if line == "memstats_"+name+" "+value {
+				foundValue = true
+			}
+			if line == "# TYPE memstats_"+name+" "+typ {
+				foundType = true
+			}
+			if foundValue && foundType {
+				return
+			}
+		}
+		t.Errorf("memstats_%s foundType=%v foundValue=%v", name, foundType, foundValue)
+	}
+
+	t.Logf("memstats:\n %s", buf.String())
+
+	checkFor("heap_alloc", "gauge", "7")
+	checkFor("total_alloc", "counter", "2")
+	checkFor("sys", "gauge", "3")
+	checkFor("mallocs", "counter", "5")
+	checkFor("frees", "counter", "6")
+	checkFor("num_gc", "counter", "26")
+	checkFor("gc_cpu_fraction", "gauge", "0.28")
+
+	if !racebuild.On {
+		if allocs := testing.AllocsPerRun(1000, func() {
+			buf.Reset()
+			writeMemstats(&buf, memstats)
+		}); allocs != 1 {
+			t.Errorf("allocs = %v; want max %v", allocs, 1)
+		}
+	}
+}