testing: with -benchtime=1x, run the benchmark loop exactly once
Like with -benchtime=1ns, if we find that the "discovery" round (run1)
has already crossed the -benchtime threshold, we skip running more
iterations.
Fixes #32051
Change-Id: I76aaef2ba521ba8ad6bbde2b14977e191aada5e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/331089
Trust: Caleb Spare <cespare@gmail.com>
Run-TryBot: Caleb Spare <cespare@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
diff --git a/src/cmd/go/testdata/script/test_benchmark_1x.txt b/src/cmd/go/testdata/script/test_benchmark_1x.txt
new file mode 100644
index 0000000..b1d4c39
--- /dev/null
+++ b/src/cmd/go/testdata/script/test_benchmark_1x.txt
@@ -0,0 +1,37 @@
+# Test that -benchtime 1x only runs a total of 1 loop iteration.
+# See golang.org/issue/32051.
+
+go test -run ^$ -bench . -benchtime 1x
+
+-- go.mod --
+module bench
+
+go 1.16
+-- x_test.go --
+package bench
+
+import (
+ "fmt"
+ "os"
+ "testing"
+)
+
+var called = false
+
+func TestMain(m *testing.M) {
+ m.Run()
+ if !called {
+ fmt.Println("benchmark never called")
+ os.Exit(1)
+ }
+}
+
+func Benchmark(b *testing.B) {
+ if b.N > 1 {
+ b.Fatalf("called with b.N=%d; want b.N=1 only", b.N)
+ }
+ if called {
+ b.Fatal("called twice")
+ }
+ called = true
+}
diff --git a/src/testing/benchmark.go b/src/testing/benchmark.go
index 30fa106..1ce637e 100644
--- a/src/testing/benchmark.go
+++ b/src/testing/benchmark.go
@@ -299,7 +299,12 @@
// Run the benchmark for at least the specified amount of time.
if b.benchTime.n > 0 {
- b.runN(b.benchTime.n)
+ // We already ran a single iteration in run1.
+ // If -benchtime=1x was requested, use that result.
+ // See https://golang.org/issue/32051.
+ if b.benchTime.n > 1 {
+ b.runN(b.benchTime.n)
+ }
} else {
d := b.benchTime.d
for n := int64(1); !b.failed && b.duration < d && n < 1e9; {
