[dev.power64] all: merge default (dd5014ed9b01) into dev.power64

Still passes on amd64.

LGTM=austin
R=austin
CC=golang-codereviews
https://golang.org/cl/165110043

2 files changed, 34 insertions, 9 deletions

diff --git a/src/runtime/debug/garbage.go b/src/runtime/debug/garbage.go
index 30994f2196..4a77dcfcd6 100644
--- a/src/runtime/debug/garbage.go
+++ b/src/runtime/debug/garbage.go
@@ -16,6 +16,7 @@ type GCStats struct {
 	NumGC          int64           // number of garbage collections
 	PauseTotal     time.Duration   // total pause for all collections
 	Pause          []time.Duration // pause history, most recent first
+	PauseEnd       []time.Time     // pause end times history, most recent first
 	PauseQuantiles []time.Duration
 }
 
@@ -30,25 +31,36 @@ type GCStats struct {
 func ReadGCStats(stats *GCStats) {
 	// Create a buffer with space for at least two copies of the
 	// pause history tracked by the runtime. One will be returned
-	// to the caller and the other will be used as a temporary buffer
-	// for computing quantiles.
+	// to the caller and the other will be used as transfer buffer
+	// for end times history and as a temporary buffer for
+	// computing quantiles.
 	const maxPause = len(((*runtime.MemStats)(nil)).PauseNs)
-	if cap(stats.Pause) < 2*maxPause {
-		stats.Pause = make([]time.Duration, 2*maxPause)
+	if cap(stats.Pause) < 2*maxPause+3 {
+		stats.Pause = make([]time.Duration, 2*maxPause+3)
 	}
 
-	// readGCStats fills in the pause history (up to maxPause entries)
-	// and then three more: Unix ns time of last GC, number of GC,
-	// and total pause time in nanoseconds. Here we depend on the
-	// fact that time.Duration's native unit is nanoseconds, so the
-	// pauses and the total pause time do not need any conversion.
+	// readGCStats fills in the pause and end times histories (up to
+	// maxPause entries) and then three more: Unix ns time of last GC,
+	// number of GC, and total pause time in nanoseconds. Here we
+	// depend on the fact that time.Duration's native unit is
+	// nanoseconds, so the pauses and the total pause time do not need
+	// any conversion.
 	readGCStats(&stats.Pause)
 	n := len(stats.Pause) - 3
 	stats.LastGC = time.Unix(0, int64(stats.Pause[n]))
 	stats.NumGC = int64(stats.Pause[n+1])
 	stats.PauseTotal = stats.Pause[n+2]
+	n /= 2 // buffer holds pauses and end times
 	stats.Pause = stats.Pause[:n]
 
+	if cap(stats.PauseEnd) < maxPause {
+		stats.PauseEnd = make([]time.Time, 0, maxPause)
+	}
+	stats.PauseEnd = stats.PauseEnd[:0]
+	for _, ns := range stats.Pause[n : n+n] {
+		stats.PauseEnd = append(stats.PauseEnd, time.Unix(0, int64(ns)))
+	}
+
 	if len(stats.PauseQuantiles) > 0 {
 		if n == 0 {
 			for i := range stats.PauseQuantiles {
diff --git a/src/runtime/debug/garbage_test.go b/src/runtime/debug/garbage_test.go
index 149bafc6f3..54c33bd4f3 100644
--- a/src/runtime/debug/garbage_test.go
+++ b/src/runtime/debug/garbage_test.go
@@ -70,6 +70,19 @@ func TestReadGCStats(t *testing.T) {
 			t.Errorf("stats.PauseQuantiles[%d]=%d > stats.PauseQuantiles[%d]=%d", i, q[i], i+1, q[i+1])
 		}
 	}
+
+	// compare memory stats with gc stats:
+	if len(stats.PauseEnd) != n {
+		t.Fatalf("len(stats.PauseEnd) = %d, want %d", len(stats.PauseEnd), n)
+	}
+	off := (int(mstats.NumGC) + len(mstats.PauseEnd) - 1) % len(mstats.PauseEnd)
+	for i := 0; i < n; i++ {
+		dt := stats.PauseEnd[i]
+		if dt.UnixNano() != int64(mstats.PauseEnd[off]) {
+			t.Errorf("stats.PauseEnd[%d] = %d, want %d", i, dt, mstats.PauseEnd[off])
+		}
+		off = (off + len(mstats.PauseEnd) - 1) % len(mstats.PauseEnd)
+	}
 }
 
 var big = make([]byte, 1<<20)