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tsweb/varz: export GC CPU fraction gauge

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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>
This commit is contained in:
James Tucker
2025-04-28 09:04:02 -07:00
committed by James Tucker
parent 189e03e741
commit b95e8bf4a1
5 changed files with 128 additions and 17 deletions
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63
tsweb/varz/varz.go
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@@ -5,6 +5,7 @@
package varz
import (
"bufio"
"cmp"
"expvar"
"fmt"
@@ -13,13 +14,16 @@ import (
"reflect"
"runtime"
"sort"
"strconv"
"strings"
"sync"
"time"
"unicode"
"unicode/utf8"
"golang.org/x/exp/constraints"
"tailscale.com/metrics"
"tailscale.com/types/logger"
"tailscale.com/version"
)
@@ -316,21 +320,52 @@ type PrometheusMetricsReflectRooter interface {
var expvarDo = expvar.Do // pulled out for tests
func writeMemstats(w io.Writer, ms *runtime.MemStats) {
out := func(name, typ string, v uint64, help string) {
if help != "" {
fmt.Fprintf(w, "# HELP memstats_%s %s\n", name, help)
}
fmt.Fprintf(w, "# TYPE memstats_%s %s\nmemstats_%s %v\n", name, typ, name, v)
func writeMemstat[V constraints.Integer | constraints.Float](bw *bufio.Writer, typ, name string, v V, help string) {
if help != "" {
bw.WriteString("# HELP memstats_")
bw.WriteString(name)
bw.WriteString(" ")
bw.WriteString(help)
bw.WriteByte('\n')
}
g := func(name string, v uint64, help string) { out(name, "gauge", v, help) }
c := func(name string, v uint64, help string) { out(name, "counter", v, help) }
g("heap_alloc", ms.HeapAlloc, "current bytes of allocated heap objects (up/down smoothly)")
c("total_alloc", ms.TotalAlloc, "cumulative bytes allocated for heap objects")
g("sys", ms.Sys, "total bytes of memory obtained from the OS")
c("mallocs", ms.Mallocs, "cumulative count of heap objects allocated")
c("frees", ms.Frees, "cumulative count of heap objects freed")
c("num_gc", uint64(ms.NumGC), "number of completed GC cycles")
bw.WriteString("# TYPE memstats_")
bw.WriteString(name)
bw.WriteString(" ")
bw.WriteString(typ)
bw.WriteByte('\n')
bw.WriteString("memstats_")
bw.WriteString(name)
bw.WriteByte(' ')
rt := reflect.TypeOf(v)
switch {
case rt == reflect.TypeFor[int]() ||
rt == reflect.TypeFor[uint]() ||
rt == reflect.TypeFor[int8]() ||
rt == reflect.TypeFor[uint8]() ||
rt == reflect.TypeFor[int16]() ||
rt == reflect.TypeFor[uint16]() ||
rt == reflect.TypeFor[int32]() ||
rt == reflect.TypeFor[uint32]() ||
rt == reflect.TypeFor[int64]() ||
rt == reflect.TypeFor[uint64]() ||
rt == reflect.TypeFor[uintptr]():
bw.Write(strconv.AppendInt(bw.AvailableBuffer(), int64(v), 10))
case rt == reflect.TypeFor[float32]() || rt == reflect.TypeFor[float64]():
bw.Write(strconv.AppendFloat(bw.AvailableBuffer(), float64(v), 'f', -1, 64))
}
bw.WriteByte('\n')
}
func writeMemstats(w io.Writer, ms *runtime.MemStats) {
fmt.Fprintf(w, "%v", logger.ArgWriter(func(bw *bufio.Writer) {
writeMemstat(bw, "gauge", "heap_alloc", ms.HeapAlloc, "current bytes of allocated heap objects (up/down smoothly)")
writeMemstat(bw, "counter", "total_alloc", ms.TotalAlloc, "cumulative bytes allocated for heap objects")
writeMemstat(bw, "gauge", "sys", ms.Sys, "total bytes of memory obtained from the OS")
writeMemstat(bw, "counter", "mallocs", ms.Mallocs, "cumulative count of heap objects allocated")
writeMemstat(bw, "counter", "frees", ms.Frees, "cumulative count of heap objects freed")
writeMemstat(bw, "counter", "num_gc", ms.NumGC, "number of completed GC cycles")
writeMemstat(bw, "gauge", "gc_cpu_fraction", ms.GCCPUFraction, "fraction of CPU time used by GC")
}))
}
// sortedStructField is metadata about a struct field used both for sorting once