experiment with getclock syscall

Author: jschaf

go.mod

@@ -1,3 +1,4 @@
 module github.com/jschaf/observe
 
 go 1.24.2
+

internal/epoch/nanos.go

@@ -19,9 +19,6 @@ func NewNanos(t time.Time) Nanos {
 	return Nanos(t.UnixNano())
 }
 
-// NanosNow returns the current time in nanoseconds since the epoch.
-func NanosNow() Nanos { return Nanos(time.Now().UnixNano()) }
-
 // ToTime converts the Nanos to a time.Time. If the value is zero, it
 // returns the zero-value of time.Time.
 //

internal/epoch/now.go

@@ -0,0 +1,6 @@
+//go:build !unix
+
+package epoch
+
+// Now returns the current time in nanoseconds since the epoch.
+func Now() Nanos { return Nanos(time.Now().UnixNano()) }

internal/epoch/now_unix.go

@@ -0,0 +1,17 @@
+//go:build unix
+
+package epoch
+
+import (
+	"syscall"
+	"time"
+)
+
+func Now() Nanos {
+	var tv syscall.Timeval
+	err := syscall.Gettimeofday(&tv)
+	if err != nil {
+		return Nanos(time.Now().UnixNano())
+	}
+	return Nanos(tv.Nano())
+}

internal/epoch/now_unix_test.go

@@ -0,0 +1,22 @@
+package epoch
+
+import (
+	"testing"
+	"time"
+)
+
+// Benchmarks as of 2025-04-28:
+// BenchmarkNow/unix_epoch.Now   72574975    14.64 ns/op
+// BenchmarkNow/time_Now         38530129	   31.12 ns/op
+func BenchmarkNow_unix(b *testing.B) {
+	b.Run("unix epoch.Now", func(b *testing.B) {
+		for b.Loop() {
+			Now()
+		}
+	})
+	b.Run("time Now", func(b *testing.B) {
+		for b.Loop() {
+			time.Now().UnixNano()
+		}
+	})
+}

trace/span.go

@@ -45,14 +45,14 @@ func (s *Span) EndTime() time.Time {
 }
 
 type spanEndConfig struct {
-	endTime epoch.Nanos
+	end epoch.Nanos
 }
 
 type SpanEndOption func(*spanEndConfig)
 
 // WithEndTime sets the end time of the span.
 func WithEndTime(t time.Time) SpanEndOption {
-	return func(cfg *spanEndConfig) { cfg.endTime = epoch.NewNanos(t) }
+	return func(cfg *spanEndConfig) { cfg.end = epoch.NewNanos(t) }
 }
 
 // End signals the span has ended.
@@ -65,12 +65,12 @@ func (s *Span) End(opts ...SpanEndOption) {
 	for _, opt := range opts {
 		opt(&cfg)
 	}
-	if cfg.endTime == 0 {
-		cfg.endTime = epoch.NanosNow()
+	if cfg.end == 0 {
+		cfg.end = epoch.Now()
 	}
 
 	// The first call sets the end time. Ignore all later calls.
-	if !(&s.end).SwapIfZero(cfg.endTime) {
+	if !(&s.end).SwapIfZero(cfg.end) {
 		return
 	}
 }

trace/tracer.go

@@ -10,13 +10,13 @@ import (
 type Tracer struct{}
 
 type startConfig struct {
-	startTime epoch.Nanos
+	start epoch.Nanos
 }
 
 type SpanStartOption func(*startConfig)
 
 func WithStartTime(t time.Time) SpanStartOption {
-	return func(cfg *startConfig) { cfg.startTime = epoch.NewNanos(t) }
+	return func(cfg *startConfig) { cfg.start = epoch.NewNanos(t) }
 }
 
 // Start starts a Span and returns a new context containing the Span.
@@ -25,14 +25,14 @@ func (t *Tracer) Start(ctx context.Context, name string, opts ...SpanStartOption
 	for _, opt := range opts {
 		opt(&cfg)
 	}
-	if cfg.startTime == 0 {
-		cfg.startTime = epoch.NanosNow()
+	if cfg.start == 0 {
+		cfg.start = epoch.Now()
 	}
 
 	span := &Span{
 		name:   name,
 		tracer: t,
-		start:  cfg.startTime,
+		start:  cfg.start,
 	}
 
 	return ctx, span