cmd/bench: export runstamp configuration key

The runstamp is a nanosecond-precision UTC timestamp that indicates when
a benchmark run started. It exists to help prevent comparing results
from different runs, which are generally applicable to compare (machine
conditions, among other things, can change over time).

Change-Id: I5385ba5548033747cbbe9b5f59a5c19b26c3bad3
Reviewed-by: Michael Pratt <>
Run-TryBot: Michael Knyszek <>
Trust: Michael Knyszek <>
TryBot-Result: Gopher Robot <>
diff --git a/cmd/bench/main.go b/cmd/bench/main.go
index 0b8e216..f4a5ac1 100644
--- a/cmd/bench/main.go
+++ b/cmd/bench/main.go
@@ -17,6 +17,7 @@
+	"time"
@@ -61,6 +62,8 @@
 func run(tcs []*toolchain) error {
+	fmt.Printf("runstamp: %s\n", time.Now().In(time.UTC).Format(time.RFC3339Nano))
 	// Because each of the functions below is responsible for running
 	// benchmarks under each toolchain itself, it is also responsible
 	// for ensuring that the benchmark tag "toolchain" is printed.