runtime/trace: add simple benchmarks for user annotation

Also, avoid Region creation when tracing is disabled.
Unfortunate side-effect of this change is that we no longer trace
pre-existing regions in tracing, but we can add the feature in
the future when we find it useful and justifiable. Until then,
let's avoid the overhead from this low-level api use as much as
possible.

goos: linux
goarch: amd64
pkg: runtime/trace

// Trace disabled
BenchmarkStartRegion-12 2000000000	         0.66 ns/op	       0 B/op	       0 allocs/op
BenchmarkNewTask-12    	30000000	        40.4 ns/op	      56 B/op	       2 allocs/op

// Trace enabled, -trace=/dev/null
BenchmarkStartRegion-12  5000000	       287 ns/op	      32 B/op	       1 allocs/op
BenchmarkNewTask-12    	 5000000	       283 ns/op	      56 B/op	       2 allocs/op

Also, skip other tests if tracing is already enabled.

Change-Id: Id3028d60b5642fcab4b09a74fd7d79361a3861e5
Reviewed-on: https://go-review.googlesource.com/109115
Reviewed-by: Peter Weinberger <pjw@google.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/runtime/trace/trace_stack_test.go b/src/runtime/trace/trace_stack_test.go
index e7b8d57659..62c06e67d9 100644
--- a/src/runtime/trace/trace_stack_test.go
+++ b/src/runtime/trace/trace_stack_test.go
@@ -24,7 +24,7 @@ import (
 // In particular that we strip bottom uninteresting frames like goexit,
 // top uninteresting frames (runtime guts).
 func TestTraceSymbolize(t *testing.T) {
-	testenv.MustHaveGoBuild(t)
+	skipTraceSymbolizeTestIfNecessary(t)
 
 	buf := new(bytes.Buffer)
 	if err := Start(buf); err != nil {
@@ -285,6 +285,13 @@ func TestTraceSymbolize(t *testing.T) {
 	}
 }
 
+func skipTraceSymbolizeTestIfNecessary(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	if IsEnabled() {
+		t.Skip("skipping because -test.trace is set")
+	}
+}
+
 func dumpEventStacks(typ byte, events []*trace.Event) ([]byte, int) {
 	matched := 0
 	o := new(bytes.Buffer)